1 <?xml version='1.0' encoding='utf-8'?>
2 <chapter xmlns="http://docbook.org/ns/docbook"
3 xmlns:xl="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en-US"
5 <title xml:id="lustretuning.title">Tuning a Lustre File System</title>
6 <para>This chapter contains information about tuning a Lustre file system for
7 better performance.</para>
9 <para>Many options in the Lustre software are set by means of kernel module
10 parameters. These parameters are contained in the
11 <literal>/etc/modprobe.d/lustre.conf</literal> file.</para>
13 <section xml:id="dbdoclet.50438272_55226">
16 <primary>tuning</primary>
19 <primary>tuning</primary>
20 <secondary>service threads</secondary>
21 </indexterm>Optimizing the Number of Service Threads</title>
22 <para>An OSS can have a minimum of two service threads and a maximum of 512
23 service threads. The number of service threads is a function of how much
24 RAM and how many CPUs are on each OSS node (1 thread / 128MB * num_cpus).
25 If the load on the OSS node is high, new service threads will be started in
26 order to process more requests concurrently, up to 4x the initial number of
27 threads (subject to the maximum of 512). For a 2GB 2-CPU system, the
28 default thread count is 32 and the maximum thread count is 128.</para>
29 <para>Increasing the size of the thread pool may help when:</para>
32 <para>Several OSTs are exported from a single OSS</para>
35 <para>Back-end storage is running synchronously</para>
38 <para>I/O completions take excessive time due to slow storage</para>
41 <para>Decreasing the size of the thread pool may help if:</para>
44 <para>Clients are overwhelming the storage capacity</para>
47 <para>There are lots of "slow I/O" or similar messages</para>
50 <para>Increasing the number of I/O threads allows the kernel and storage to
51 aggregate many writes together for more efficient disk I/O. The OSS thread
52 pool is shared--each thread allocates approximately 1.5 MB (maximum RPC
53 size + 0.5 MB) for internal I/O buffers.</para>
54 <para>It is very important to consider memory consumption when increasing
55 the thread pool size. Drives are only able to sustain a certain amount of
56 parallel I/O activity before performance is degraded, due to the high
57 number of seeks and the OST threads just waiting for I/O. In this
58 situation, it may be advisable to decrease the load by decreasing the
59 number of OST threads.</para>
60 <para>Determining the optimum number of OSS threads is a process of trial
61 and error, and varies for each particular configuration. Variables include
62 the number of OSTs on each OSS, number and speed of disks, RAID
63 configuration, and available RAM. You may want to start with a number of
64 OST threads equal to the number of actual disk spindles on the node. If you
65 use RAID, subtract any dead spindles not used for actual data (e.g., 1 of N
66 of spindles for RAID5, 2 of N spindles for RAID6), and monitor the
67 performance of clients during usual workloads. If performance is degraded,
68 increase the thread count and see how that works until performance is
69 degraded again or you reach satisfactory performance.</para>
71 <para>If there are too many threads, the latency for individual I/O
72 requests can become very high and should be avoided. Set the desired
73 maximum thread count permanently using the method described above.</para>
78 <primary>tuning</primary>
79 <secondary>OSS threads</secondary>
80 </indexterm>Specifying the OSS Service Thread Count</title>
82 <literal>oss_num_threads</literal> parameter enables the number of OST
83 service threads to be specified at module load time on the OSS
86 options ost oss_num_threads={N}
88 <para>After startup, the minimum and maximum number of OSS thread counts
90 <literal>{service}.thread_{min,max,started}</literal> tunable. To change
91 the tunable at runtime, run:</para>
94 lctl {get,set}_param {service}.thread_{min,max,started}
98 This works in a similar fashion to
99 binding of threads on MDS. MDS thread tuning is covered in
100 <xref linkend="dbdoclet.mdsbinding" />.</para>
104 <literal>oss_cpts=[EXPRESSION]</literal> binds the default OSS service
106 <literal>[EXPRESSION]</literal>.</para>
110 <literal>oss_io_cpts=[EXPRESSION]</literal> binds the IO OSS service
112 <literal>[EXPRESSION]</literal>.</para>
115 <para>For further details, see
116 <xref linkend="dbdoclet.50438271_87260" />.</para>
118 <section xml:id="dbdoclet.mdstuning">
121 <primary>tuning</primary>
122 <secondary>MDS threads</secondary>
123 </indexterm>Specifying the MDS Service Thread Count</title>
125 <literal>mds_num_threads</literal> parameter enables the number of MDS
126 service threads to be specified at module load time on the MDS
128 <screen>options mds mds_num_threads={N}</screen>
129 <para>After startup, the minimum and maximum number of MDS thread counts
131 <literal>{service}.thread_{min,max,started}</literal> tunable. To change
132 the tunable at runtime, run:</para>
135 lctl {get,set}_param {service}.thread_{min,max,started}
138 <para>For details, see
139 <xref linkend="dbdoclet.50438271_87260" />.</para>
140 <para>The number of MDS service threads started depends on system size
141 and the load on the server, and has a default maximum of 64. The
142 maximum potential number of threads (<literal>MDS_MAX_THREADS</literal>)
145 <para>The OSS and MDS start two threads per service per CPT at mount
146 time, and dynamically increase the number of running service threads in
147 response to server load. Setting the <literal>*_num_threads</literal>
148 module parameter starts the specified number of threads for that
149 service immediately and disables automatic thread creation behavior.
152 <para>Parameters are available to provide administrators control
153 over the number of service threads.</para>
157 <literal>mds_rdpg_num_threads</literal> controls the number of threads
158 in providing the read page service. The read page service handles
159 file close and readdir operations.</para>
163 <literal>mds_attr_num_threads</literal> controls the number of threads
164 in providing the setattr service to clients running Lustre software
170 <section xml:id="dbdoclet.mdsbinding">
173 <primary>tuning</primary>
174 <secondary>MDS binding</secondary>
175 </indexterm>Binding MDS Service Thread to CPU Partitions</title>
176 <para>With the Node Affinity (<xref linkend="nodeaffdef" />) feature,
177 MDS threads can be bound to particular CPU partitions (CPTs) to improve CPU
178 cache usage and memory locality. Default values for CPT counts and CPU core
179 bindings are selected automatically to provide good overall performance for
180 a given CPU count. However, an administrator can deviate from these setting
181 if they choose. For details on specifying the mapping of CPU cores to
182 CPTs see <xref linkend="dbdoclet.libcfstuning"/>.
187 <literal>mds_num_cpts=[EXPRESSION]</literal> binds the default MDS
188 service threads to CPTs defined by
189 <literal>EXPRESSION</literal>. For example
190 <literal>mds_num_cpts=[0-3]</literal> will bind the MDS service threads
192 <literal>CPT[0,1,2,3]</literal>.</para>
196 <literal>mds_rdpg_num_cpts=[EXPRESSION]</literal> binds the read page
197 service threads to CPTs defined by
198 <literal>EXPRESSION</literal>. The read page service handles file close
199 and readdir requests. For example
200 <literal>mds_rdpg_num_cpts=[4]</literal> will bind the read page threads
202 <literal>CPT4</literal>.</para>
206 <literal>mds_attr_num_cpts=[EXPRESSION]</literal> binds the setattr
207 service threads to CPTs defined by
208 <literal>EXPRESSION</literal>.</para>
211 <para>Parameters must be set before module load in the file
212 <literal>/etc/modprobe.d/lustre.conf</literal>. For example:
213 <example><title>lustre.conf</title>
214 <screen>options lnet networks=tcp0(eth0)
215 options mdt mds_num_cpts=[0]</screen>
219 <section xml:id="dbdoclet.50438272_73839">
222 <primary>LNet</primary>
223 <secondary>tuning</secondary>
226 <primary>tuning</primary>
227 <secondary>LNet</secondary>
228 </indexterm>Tuning LNet Parameters</title>
229 <para>This section describes LNet tunables, the use of which may be
230 necessary on some systems to improve performance. To test the performance
231 of your Lustre network, see
232 <xref linkend='lnetselftest' />.</para>
234 <title>Transmit and Receive Buffer Size</title>
235 <para>The kernel allocates buffers for sending and receiving messages on
238 <literal>ksocklnd</literal> has separate parameters for the transmit and
239 receive buffers.</para>
241 options ksocklnd tx_buffer_size=0 rx_buffer_size=0
243 <para>If these parameters are left at the default value (0), the system
244 automatically tunes the transmit and receive buffer size. In almost every
245 case, this default produces the best performance. Do not attempt to tune
246 these parameters unless you are a network expert.</para>
249 <title>Hardware Interrupts (
250 <literal>enable_irq_affinity</literal>)</title>
251 <para>The hardware interrupts that are generated by network adapters may
252 be handled by any CPU in the system. In some cases, we would like network
253 traffic to remain local to a single CPU to help keep the processor cache
254 warm and minimize the impact of context switches. This is helpful when an
255 SMP system has more than one network interface and ideal when the number
256 of interfaces equals the number of CPUs. To enable the
257 <literal>enable_irq_affinity</literal> parameter, enter:</para>
259 options ksocklnd enable_irq_affinity=1
261 <para>In other cases, if you have an SMP platform with a single fast
262 interface such as 10 Gb Ethernet and more than two CPUs, you may see
263 performance improve by turning this parameter off.</para>
265 options ksocklnd enable_irq_affinity=0
267 <para>By default, this parameter is off. As always, you should test the
268 performance to compare the impact of changing this parameter.</para>
273 <primary>tuning</primary>
274 <secondary>Network interface binding</secondary>
275 </indexterm>Binding Network Interface Against CPU Partitions</title>
276 <para>Lustre allows enhanced network interface control. This means that
277 an administrator can bind an interface to one or more CPU partitions.
278 Bindings are specified as options to the LNet modules. For more
279 information on specifying module options, see
280 <xref linkend="dbdoclet.50438293_15350" /></para>
282 <literal>o2ib0(ib0)[0,1]</literal> will ensure that all messages for
283 <literal>o2ib0</literal> will be handled by LND threads executing on
284 <literal>CPT0</literal> and
285 <literal>CPT1</literal>. An additional example might be:
286 <literal>tcp1(eth0)[0]</literal>. Messages for
287 <literal>tcp1</literal> are handled by threads on
288 <literal>CPT0</literal>.</para>
293 <primary>tuning</primary>
294 <secondary>Network interface credits</secondary>
295 </indexterm>Network Interface Credits</title>
296 <para>Network interface (NI) credits are shared across all CPU partitions
297 (CPT). For example, if a machine has four CPTs and the number of NI
298 credits is 512, then each partition has 128 credits. If a large number of
299 CPTs exist on the system, LNet checks and validates the NI credits for
300 each CPT to ensure each CPT has a workable number of credits. For
301 example, if a machine has 16 CPTs and the number of NI credits is 256,
302 then each partition only has 16 credits. 16 NI credits is low and could
303 negatively impact performance. As a result, LNet automatically adjusts
305 <literal>peer_credits</literal>(
306 <literal>peer_credits</literal> is 8 by default), so each partition has 64
308 <para>Increasing the number of
309 <literal>credits</literal>/
310 <literal>peer_credits</literal> can improve the performance of high
311 latency networks (at the cost of consuming more memory) by enabling LNet
312 to send more inflight messages to a specific network/peer and keep the
313 pipeline saturated.</para>
314 <para>An administrator can modify the NI credit count using
315 <literal>ksoclnd</literal> or
316 <literal>ko2iblnd</literal>. In the example below, 256 credits are
317 applied to TCP connections.</para>
321 <para>Applying 256 credits to IB connections can be achieved with:</para>
326 <para>LNet may revalidate the NI credits, so the administrator's
327 request may not persist.</para>
333 <primary>tuning</primary>
334 <secondary>router buffers</secondary>
335 </indexterm>Router Buffers</title>
336 <para>When a node is set up as an LNet router, three pools of buffers are
337 allocated: tiny, small and large. These pools are allocated per CPU
338 partition and are used to buffer messages that arrive at the router to be
339 forwarded to the next hop. The three different buffer sizes accommodate
340 different size messages.</para>
341 <para>If a message arrives that can fit in a tiny buffer then a tiny
342 buffer is used, if a message doesn’t fit in a tiny buffer, but fits in a
343 small buffer, then a small buffer is used. Finally if a message does not
344 fit in either a tiny buffer or a small buffer, a large buffer is
346 <para>Router buffers are shared by all CPU partitions. For a machine with
347 a large number of CPTs, the router buffer number may need to be specified
348 manually for best performance. A low number of router buffers risks
349 starving the CPU partitions of resources.</para>
353 <literal>tiny_router_buffers</literal>: Zero payload buffers used for
354 signals and acknowledgements.</para>
358 <literal>small_router_buffers</literal>: 4 KB payload buffers for
359 small messages</para>
363 <literal>large_router_buffers</literal>: 1 MB maximum payload
364 buffers, corresponding to the recommended RPC size of 1 MB.</para>
367 <para>The default setting for router buffers typically results in
368 acceptable performance. LNet automatically sets a default value to reduce
369 the likelihood of resource starvation. The size of a router buffer can be
370 modified as shown in the example below. In this example, the size of the
371 large buffer is modified using the
372 <literal>large_router_buffers</literal> parameter.</para>
374 lnet large_router_buffers=8192
377 <para>LNet may revalidate the router buffer setting, so the
378 administrator's request may not persist.</para>
384 <primary>tuning</primary>
385 <secondary>portal round-robin</secondary>
386 </indexterm>Portal Round-Robin</title>
387 <para>Portal round-robin defines the policy LNet applies to deliver
388 events and messages to the upper layers. The upper layers are PLRPC
389 service or LNet selftest.</para>
390 <para>If portal round-robin is disabled, LNet will deliver messages to
391 CPTs based on a hash of the source NID. Hence, all messages from a
392 specific peer will be handled by the same CPT. This can reduce data
393 traffic between CPUs. However, for some workloads, this behavior may
394 result in poorly balancing loads across the CPU.</para>
395 <para>If portal round-robin is enabled, LNet will round-robin incoming
396 events across all CPTs. This may balance load better across the CPU but
397 can incur a cross CPU overhead.</para>
398 <para>The current policy can be changed by an administrator with
400 <replaceable>value</replaceable>>
401 /proc/sys/lnet/portal_rotor</literal>. There are four options for
403 <replaceable>value</replaceable>
408 <literal>OFF</literal>
410 <para>Disable portal round-robin on all incoming requests.</para>
414 <literal>ON</literal>
416 <para>Enable portal round-robin on all incoming requests.</para>
420 <literal>RR_RT</literal>
422 <para>Enable portal round-robin only for routed messages.</para>
426 <literal>HASH_RT</literal>
428 <para>Routed messages will be delivered to the upper layer by hash of
429 source NID (instead of NID of router.) This is the default
435 <title>LNet Peer Health</title>
436 <para>Two options are available to help determine peer health:
440 <literal>peer_timeout</literal>- The timeout (in seconds) before an
441 aliveness query is sent to a peer. For example, if
442 <literal>peer_timeout</literal> is set to
443 <literal>180sec</literal>, an aliveness query is sent to the peer
444 every 180 seconds. This feature only takes effect if the node is
445 configured as an LNet router.</para>
446 <para>In a routed environment, the
447 <literal>peer_timeout</literal> feature should always be on (set to a
448 value in seconds) on routers. If the router checker has been enabled,
449 the feature should be turned off by setting it to 0 on clients and
451 <para>For a non-routed scenario, enabling the
452 <literal>peer_timeout</literal> option provides health information
453 such as whether a peer is alive or not. For example, a client is able
454 to determine if an MGS or OST is up when it sends it a message. If a
455 response is received, the peer is alive; otherwise a timeout occurs
456 when the request is made.</para>
458 <literal>peer_timeout</literal> should be set to no less than the LND
459 timeout setting. For more information about LND timeouts, see
460 <xref xmlns:xlink="http://www.w3.org/1999/xlink"
461 linkend="section_c24_nt5_dl" />.</para>
463 <literal>o2iblnd</literal>(IB) driver is used,
464 <literal>peer_timeout</literal> should be at least twice the value of
466 <literal>ko2iblnd</literal> keepalive option. for more information
467 about keepalive options, see
468 <xref xmlns:xlink="http://www.w3.org/1999/xlink"
469 linkend="section_ngq_qhy_zl" />.</para>
473 <literal>avoid_asym_router_failure</literal>– When set to 1, the
474 router checker running on the client or a server periodically pings
475 all the routers corresponding to the NIDs identified in the routes
476 parameter setting on the node to determine the status of each router
477 interface. The default setting is 1. (For more information about the
478 LNet routes parameter, see
479 <xref xmlns:xlink="http://www.w3.org/1999/xlink"
480 linkend="lnet_module_routes" /></para>
481 <para>A router is considered down if any of its NIDs are down. For
482 example, router X has three NIDs:
483 <literal>Xnid1</literal>,
484 <literal>Xnid2</literal>, and
485 <literal>Xnid3</literal>. A client is connected to the router via
486 <literal>Xnid1</literal>. The client has router checker enabled. The
487 router checker periodically sends a ping to the router via
488 <literal>Xnid1</literal>. The router responds to the ping with the
489 status of each of its NIDs. In this case, it responds with
490 <literal>Xnid1=up</literal>,
491 <literal>Xnid2=up</literal>,
492 <literal>Xnid3=down</literal>. If
493 <literal>avoid_asym_router_failure==1</literal>, the router is
494 considered down if any of its NIDs are down, so router X is
495 considered down and will not be used for routing messages. If
496 <literal>avoid_asym_router_failure==0</literal>, router X will
497 continue to be used for routing messages.</para>
499 </itemizedlist></para>
500 <para>The following router checker parameters must be set to the maximum
501 value of the corresponding setting for this option on any client or
506 <literal>dead_router_check_interval</literal>
511 <literal>live_router_check_interval</literal>
516 <literal>router_ping_timeout</literal>
519 </itemizedlist></para>
520 <para>For example, the
521 <literal>dead_router_check_interval</literal> parameter on any router must
525 <section xml:id="dbdoclet.libcfstuning">
528 <primary>tuning</primary>
529 <secondary>libcfs</secondary>
530 </indexterm>libcfs Tuning</title>
531 <para>Lustre allows binding service threads via CPU Partition Tables
532 (CPTs). This allows the system administrator to fine-tune on which CPU
533 cores the Lustre service threads are run, for both OSS and MDS services,
534 as well as on the client.
536 <para>CPTs are useful to reserve some cores on the OSS or MDS nodes for
537 system functions such as system monitoring, HA heartbeat, or similar
538 tasks. On the client it may be useful to restrict Lustre RPC service
539 threads to a small subset of cores so that they do not interfere with
540 computation, or because these cores are directly attached to the network
543 <para>By default, the Lustre software will automatically generate CPU
544 partitions (CPT) based on the number of CPUs in the system.
545 The CPT count can be explicitly set on the libcfs module using
546 <literal>cpu_npartitions=<replaceable>NUMBER</replaceable></literal>.
547 The value of <literal>cpu_npartitions</literal> must be an integer between
548 1 and the number of online CPUs.
550 <para condition='l29'>In Lustre 2.9 and later the default is to use
551 one CPT per NUMA node. In earlier versions of Lustre, by default there
552 was a single CPT if the online CPU core count was four or fewer, and
553 additional CPTs would be created depending on the number of CPU cores,
554 typically with 4-8 cores per CPT.
557 <para>Setting <literal>cpu_npartitions=1</literal> will disable most
558 of the SMP Node Affinity functionality.</para>
561 <title>CPU Partition String Patterns</title>
562 <para>CPU partitions can be described using string pattern notation.
563 If <literal>cpu_pattern=N</literal> is used, then there will be one
564 CPT for each NUMA node in the system, with each CPT mapping all of
565 the CPU cores for that NUMA node.
567 <para>It is also possible to explicitly specify the mapping between
568 CPU cores and CPTs, for example:</para>
572 <literal>cpu_pattern="0[2,4,6] 1[3,5,7]</literal>
574 <para>Create two CPTs, CPT0 contains cores 2, 4, and 6, while CPT1
575 contains cores 3, 5, 7. CPU cores 0 and 1 will not be used by Lustre
576 service threads, and could be used for node services such as
577 system monitoring, HA heartbeat threads, etc. The binding of
578 non-Lustre services to those CPU cores may be done in userspace
579 using <literal>numactl(8)</literal> or other application-specific
580 methods, but is beyond the scope of this document.</para>
584 <literal>cpu_pattern="N 0[0-3] 1[4-7]</literal>
586 <para>Create two CPTs, with CPT0 containing all CPUs in NUMA
587 node[0-3], while CPT1 contains all CPUs in NUMA node [4-7].</para>
590 <para>The current configuration of the CPU partition can be read via
591 <literal>lctl get_parm cpu_partition_table</literal>. For example,
592 a simple 4-core system has a single CPT with all four CPU cores:
593 <screen>$ lctl get_param cpu_partition_table
594 cpu_partition_table=0 : 0 1 2 3</screen>
595 while a larger NUMA system with four 12-core CPUs may have four CPTs:
596 <screen>$ lctl get_param cpu_partition_table
598 0 : 0 1 2 3 4 5 6 7 8 9 10 11
599 1 : 12 13 14 15 16 17 18 19 20 21 22 23
600 2 : 24 25 26 27 28 29 30 31 32 33 34 35
601 3 : 36 37 38 39 40 41 42 43 44 45 46 47
606 <section xml:id="dbdoclet.lndtuning">
609 <primary>tuning</primary>
610 <secondary>LND tuning</secondary>
611 </indexterm>LND Tuning</title>
612 <para>LND tuning allows the number of threads per CPU partition to be
613 specified. An administrator can set the threads for both
614 <literal>ko2iblnd</literal> and
615 <literal>ksocklnd</literal> using the
616 <literal>nscheds</literal> parameter. This adjusts the number of threads for
617 each partition, not the overall number of threads on the LND.</para>
619 <para>Lustre software release 2.3 has greatly decreased the default
620 number of threads for
621 <literal>ko2iblnd</literal> and
622 <literal>ksocklnd</literal> on high-core count machines. The current
623 default values are automatically set and are chosen to work well across a
624 number of typical scenarios.</para>
627 <title>ko2iblnd Tuning</title>
628 <para>The following table outlines the ko2iblnd module parameters to be used
630 <informaltable frame="all">
632 <colspec colname="c1" colwidth="50*" />
633 <colspec colname="c2" colwidth="50*" />
634 <colspec colname="c3" colwidth="50*" />
639 <emphasis role="bold">Module Parameter</emphasis>
644 <emphasis role="bold">Default Value</emphasis>
649 <emphasis role="bold">Description</emphasis>
658 <literal>service</literal>
663 <literal>987</literal>
667 <para>Service number (within RDMA_PS_TCP).</para>
673 <literal>cksum</literal>
682 <para>Set non-zero to enable message (not RDMA) checksums.</para>
688 <literal>timeout</literal>
693 <literal>50</literal>
697 <para>Timeout in seconds.</para>
703 <literal>nscheds</literal>
712 <para>Number of threads in each scheduler pool (per CPT). Value of
713 zero means we derive the number from the number of cores.</para>
719 <literal>conns_per_peer</literal>
724 <literal>4 (OmniPath), 1 (Everything else)</literal>
728 <para>Introduced in 2.10. Number of connections to each peer. Messages
729 are sent round-robin over the connection pool. Provides signifiant
730 improvement with OmniPath.</para>
736 <literal>ntx</literal>
741 <literal>512</literal>
745 <para>Number of message descriptors allocated for each pool at
746 startup. Grows at runtime. Shared by all CPTs.</para>
752 <literal>credits</literal>
757 <literal>256</literal>
761 <para>Number of concurrent sends on network.</para>
767 <literal>peer_credits</literal>
776 <para>Number of concurrent sends to 1 peer. Related/limited by IB
783 <literal>peer_credits_hiw</literal>
792 <para>When eagerly to return credits.</para>
798 <literal>peer_buffer_credits</literal>
807 <para>Number per-peer router buffer credits.</para>
813 <literal>peer_timeout</literal>
818 <literal>180</literal>
822 <para>Seconds without aliveness news to declare peer dead (less than
823 or equal to 0 to disable).</para>
829 <literal>ipif_name</literal>
834 <literal>ib0</literal>
838 <para>IPoIB interface name.</para>
844 <literal>retry_count</literal>
853 <para>Retransmissions when no ACK received.</para>
859 <literal>rnr_retry_count</literal>
868 <para>RNR retransmissions.</para>
874 <literal>keepalive</literal>
879 <literal>100</literal>
883 <para>Idle time in seconds before sending a keepalive.</para>
889 <literal>ib_mtu</literal>
898 <para>IB MTU 256/512/1024/2048/4096.</para>
904 <literal>concurrent_sends</literal>
913 <para>Send work-queue sizing. If zero, derived from
914 <literal>map_on_demand</literal> and <literal>peer_credits</literal>.
921 <literal>map_on_demand</literal>
926 <literal>0 (pre-4.8 Linux) 1 (4.8 Linux onward) 32 (OmniPath)</literal>
930 <para>Number of fragments reserved for connection. If zero, use
931 global memory region (found to be security issue). If non-zero, use
932 FMR or FastReg for memory registration. Value needs to agree between
933 both peers of connection.</para>
939 <literal>fmr_pool_size</literal>
944 <literal>512</literal>
948 <para>Size of fmr pool on each CPT (>= ntx / 4). Grows at runtime.
955 <literal>fmr_flush_trigger</literal>
960 <literal>384</literal>
964 <para>Number dirty FMRs that triggers pool flush.</para>
970 <literal>fmr_cache</literal>
979 <para>Non-zero to enable FMR caching.</para>
985 <literal>dev_failover</literal>
994 <para>HCA failover for bonding (0 OFF, 1 ON, other values reserved).
1001 <literal>require_privileged_port</literal>
1006 <literal>0</literal>
1010 <para>Require privileged port when accepting connection.</para>
1016 <literal>use_privileged_port</literal>
1021 <literal>1</literal>
1025 <para>Use privileged port when initiating connection.</para>
1031 <literal>wrq_sge</literal>
1036 <literal>2</literal>
1040 <para>Introduced in 2.10. Number scatter/gather element groups per
1041 work request. Used to deal with fragmentations which can consume
1042 double the number of work requests.</para>
1050 <section xml:id="dbdoclet.nrstuning" condition='l24'>
1053 <primary>tuning</primary>
1054 <secondary>Network Request Scheduler (NRS) Tuning</secondary>
1055 </indexterm>Network Request Scheduler (NRS) Tuning</title>
1056 <para>The Network Request Scheduler (NRS) allows the administrator to
1057 influence the order in which RPCs are handled at servers, on a per-PTLRPC
1058 service basis, by providing different policies that can be activated and
1059 tuned in order to influence the RPC ordering. The aim of this is to provide
1060 for better performance, and possibly discrete performance characteristics
1061 using future policies.</para>
1062 <para>The NRS policy state of a PTLRPC service can be read and set via the
1063 <literal>{service}.nrs_policies</literal> tunable. To read a PTLRPC
1064 service's NRS policy state, run:</para>
1066 lctl get_param {service}.nrs_policies
1068 <para>For example, to read the NRS policy state of the
1069 <literal>ost_io</literal> service, run:</para>
1071 $ lctl get_param ost.OSS.ost_io.nrs_policies
1072 ost.OSS.ost_io.nrs_policies=
1111 high_priority_requests:
1149 <para>NRS policy state is shown in either one or two sections, depending on
1150 the PTLRPC service being queried. The first section is named
1151 <literal>regular_requests</literal> and is available for all PTLRPC
1152 services, optionally followed by a second section which is named
1153 <literal>high_priority_requests</literal>. This is because some PTLRPC
1154 services are able to treat some types of RPCs as higher priority ones, such
1155 that they are handled by the server with higher priority compared to other,
1156 regular RPC traffic. For PTLRPC services that do not support high-priority
1157 RPCs, you will only see the
1158 <literal>regular_requests</literal> section.</para>
1159 <para>There is a separate instance of each NRS policy on each PTLRPC
1160 service for handling regular and high-priority RPCs (if the service
1161 supports high-priority RPCs). For each policy instance, the following
1162 fields are shown:</para>
1163 <informaltable frame="all">
1165 <colspec colname="c1" colwidth="50*" />
1166 <colspec colname="c2" colwidth="50*" />
1171 <emphasis role="bold">Field</emphasis>
1176 <emphasis role="bold">Description</emphasis>
1185 <literal>name</literal>
1189 <para>The name of the policy.</para>
1195 <literal>state</literal>
1199 <para>The state of the policy; this can be any of
1200 <literal>invalid, stopping, stopped, starting, started</literal>.
1201 A fully enabled policy is in the
1202 <literal>started</literal> state.</para>
1208 <literal>fallback</literal>
1212 <para>Whether the policy is acting as a fallback policy or not. A
1213 fallback policy is used to handle RPCs that other enabled
1214 policies fail to handle, or do not support the handling of. The
1216 <literal>no, yes</literal>. Currently, only the FIFO policy can
1217 act as a fallback policy.</para>
1223 <literal>queued</literal>
1227 <para>The number of RPCs that the policy has waiting to be
1234 <literal>active</literal>
1238 <para>The number of RPCs that the policy is currently
1245 <para>To enable an NRS policy on a PTLRPC service run:</para>
1247 lctl set_param {service}.nrs_policies=
1248 <replaceable>policy_name</replaceable>
1250 <para>This will enable the policy
1251 <replaceable>policy_name</replaceable>for both regular and high-priority
1252 RPCs (if the PLRPC service supports high-priority RPCs) on the given
1253 service. For example, to enable the CRR-N NRS policy for the ldlm_cbd
1254 service, run:</para>
1256 $ lctl set_param ldlm.services.ldlm_cbd.nrs_policies=crrn
1257 ldlm.services.ldlm_cbd.nrs_policies=crrn
1260 <para>For PTLRPC services that support high-priority RPCs, you can also
1262 <replaceable>reg|hp</replaceable>token, in order to enable an NRS policy
1263 for handling only regular or high-priority RPCs on a given PTLRPC service,
1266 lctl set_param {service}.nrs_policies="
1267 <replaceable>policy_name</replaceable>
1268 <replaceable>reg|hp</replaceable>"
1270 <para>For example, to enable the TRR policy for handling only regular, but
1271 not high-priority RPCs on the
1272 <literal>ost_io</literal> service, run:</para>
1274 $ lctl set_param ost.OSS.ost_io.nrs_policies="trr reg"
1275 ost.OSS.ost_io.nrs_policies="trr reg"
1279 <para>When enabling an NRS policy, the policy name must be given in
1280 lower-case characters, otherwise the operation will fail with an error
1286 <primary>tuning</primary>
1287 <secondary>Network Request Scheduler (NRS) Tuning</secondary>
1288 <tertiary>first in, first out (FIFO) policy</tertiary>
1289 </indexterm>First In, First Out (FIFO) policy</title>
1290 <para>The first in, first out (FIFO) policy handles RPCs in a service in
1291 the same order as they arrive from the LNet layer, so no special
1292 processing takes place to modify the RPC handling stream. FIFO is the
1293 default policy for all types of RPCs on all PTLRPC services, and is
1294 always enabled irrespective of the state of other policies, so that it
1295 can be used as a backup policy, in case a more elaborate policy that has
1296 been enabled fails to handle an RPC, or does not support handling a given
1298 <para>The FIFO policy has no tunables that adjust its behaviour.</para>
1303 <primary>tuning</primary>
1304 <secondary>Network Request Scheduler (NRS) Tuning</secondary>
1305 <tertiary>client round-robin over NIDs (CRR-N) policy</tertiary>
1306 </indexterm>Client Round-Robin over NIDs (CRR-N) policy</title>
1307 <para>The client round-robin over NIDs (CRR-N) policy performs batched
1308 round-robin scheduling of all types of RPCs, with each batch consisting
1309 of RPCs originating from the same client node, as identified by its NID.
1310 CRR-N aims to provide for better resource utilization across the cluster,
1311 and to help shorten completion times of jobs in some cases, by
1312 distributing available bandwidth more evenly across all clients.</para>
1313 <para>The CRR-N policy can be enabled on all types of PTLRPC services,
1314 and has the following tunable that can be used to adjust its
1319 <literal>{service}.nrs_crrn_quantum</literal>
1322 <literal>{service}.nrs_crrn_quantum</literal> tunable determines the
1323 maximum allowed size of each batch of RPCs; the unit of measure is in
1324 number of RPCs. To read the maximum allowed batch size of a CRR-N
1327 lctl get_param {service}.nrs_crrn_quantum
1329 <para>For example, to read the maximum allowed batch size of a CRR-N
1330 policy on the ost_io service, run:</para>
1332 $ lctl get_param ost.OSS.ost_io.nrs_crrn_quantum
1333 ost.OSS.ost_io.nrs_crrn_quantum=reg_quantum:16
1337 <para>You can see that there is a separate maximum allowed batch size
1339 <literal>reg_quantum</literal>) and high-priority (
1340 <literal>hp_quantum</literal>) RPCs (if the PTLRPC service supports
1341 high-priority RPCs).</para>
1342 <para>To set the maximum allowed batch size of a CRR-N policy on a
1343 given service, run:</para>
1345 lctl set_param {service}.nrs_crrn_quantum=
1346 <replaceable>1-65535</replaceable>
1348 <para>This will set the maximum allowed batch size on a given
1349 service, for both regular and high-priority RPCs (if the PLRPC
1350 service supports high-priority RPCs), to the indicated value.</para>
1351 <para>For example, to set the maximum allowed batch size on the
1352 ldlm_canceld service to 16 RPCs, run:</para>
1354 $ lctl set_param ldlm.services.ldlm_canceld.nrs_crrn_quantum=16
1355 ldlm.services.ldlm_canceld.nrs_crrn_quantum=16
1358 <para>For PTLRPC services that support high-priority RPCs, you can
1359 also specify a different maximum allowed batch size for regular and
1360 high-priority RPCs, by running:</para>
1362 $ lctl set_param {service}.nrs_crrn_quantum=
1363 <replaceable>reg_quantum|hp_quantum</replaceable>:
1364 <replaceable>1-65535</replaceable>"
1366 <para>For example, to set the maximum allowed batch size on the
1367 ldlm_canceld service, for high-priority RPCs to 32, run:</para>
1369 $ lctl set_param ldlm.services.ldlm_canceld.nrs_crrn_quantum="hp_quantum:32"
1370 ldlm.services.ldlm_canceld.nrs_crrn_quantum=hp_quantum:32
1373 <para>By using the last method, you can also set the maximum regular
1374 and high-priority RPC batch sizes to different values, in a single
1375 command invocation.</para>
1382 <primary>tuning</primary>
1383 <secondary>Network Request Scheduler (NRS) Tuning</secondary>
1384 <tertiary>object-based round-robin (ORR) policy</tertiary>
1385 </indexterm>Object-based Round-Robin (ORR) policy</title>
1386 <para>The object-based round-robin (ORR) policy performs batched
1387 round-robin scheduling of bulk read write (brw) RPCs, with each batch
1388 consisting of RPCs that pertain to the same backend-file system object,
1389 as identified by its OST FID.</para>
1390 <para>The ORR policy is only available for use on the ost_io service. The
1391 RPC batches it forms can potentially consist of mixed bulk read and bulk
1392 write RPCs. The RPCs in each batch are ordered in an ascending manner,
1393 based on either the file offsets, or the physical disk offsets of each
1394 RPC (only applicable to bulk read RPCs).</para>
1395 <para>The aim of the ORR policy is to provide for increased bulk read
1396 throughput in some cases, by ordering bulk read RPCs (and potentially
1397 bulk write RPCs), and thus minimizing costly disk seek operations.
1398 Performance may also benefit from any resulting improvement in resource
1399 utilization, or by taking advantage of better locality of reference
1400 between RPCs.</para>
1401 <para>The ORR policy has the following tunables that can be used to
1402 adjust its behaviour:</para>
1406 <literal>ost.OSS.ost_io.nrs_orr_quantum</literal>
1409 <literal>ost.OSS.ost_io.nrs_orr_quantum</literal> tunable determines
1410 the maximum allowed size of each batch of RPCs; the unit of measure
1411 is in number of RPCs. To read the maximum allowed batch size of the
1412 ORR policy, run:</para>
1414 $ lctl get_param ost.OSS.ost_io.nrs_orr_quantum
1415 ost.OSS.ost_io.nrs_orr_quantum=reg_quantum:256
1419 <para>You can see that there is a separate maximum allowed batch size
1421 <literal>reg_quantum</literal>) and high-priority (
1422 <literal>hp_quantum</literal>) RPCs (if the PTLRPC service supports
1423 high-priority RPCs).</para>
1424 <para>To set the maximum allowed batch size for the ORR policy,
1427 $ lctl set_param ost.OSS.ost_io.nrs_orr_quantum=
1428 <replaceable>1-65535</replaceable>
1430 <para>This will set the maximum allowed batch size for both regular
1431 and high-priority RPCs, to the indicated value.</para>
1432 <para>You can also specify a different maximum allowed batch size for
1433 regular and high-priority RPCs, by running:</para>
1435 $ lctl set_param ost.OSS.ost_io.nrs_orr_quantum=
1436 <replaceable>reg_quantum|hp_quantum</replaceable>:
1437 <replaceable>1-65535</replaceable>
1439 <para>For example, to set the maximum allowed batch size for regular
1440 RPCs to 128, run:</para>
1442 $ lctl set_param ost.OSS.ost_io.nrs_orr_quantum=reg_quantum:128
1443 ost.OSS.ost_io.nrs_orr_quantum=reg_quantum:128
1446 <para>By using the last method, you can also set the maximum regular
1447 and high-priority RPC batch sizes to different values, in a single
1448 command invocation.</para>
1452 <literal>ost.OSS.ost_io.nrs_orr_offset_type</literal>
1455 <literal>ost.OSS.ost_io.nrs_orr_offset_type</literal> tunable
1456 determines whether the ORR policy orders RPCs within each batch based
1457 on logical file offsets or physical disk offsets. To read the offset
1458 type value for the ORR policy, run:</para>
1460 $ lctl get_param ost.OSS.ost_io.nrs_orr_offset_type
1461 ost.OSS.ost_io.nrs_orr_offset_type=reg_offset_type:physical
1462 hp_offset_type:logical
1465 <para>You can see that there is a separate offset type value for
1467 <literal>reg_offset_type</literal>) and high-priority (
1468 <literal>hp_offset_type</literal>) RPCs.</para>
1469 <para>To set the ordering type for the ORR policy, run:</para>
1471 $ lctl set_param ost.OSS.ost_io.nrs_orr_offset_type=
1472 <replaceable>physical|logical</replaceable>
1474 <para>This will set the offset type for both regular and
1475 high-priority RPCs, to the indicated value.</para>
1476 <para>You can also specify a different offset type for regular and
1477 high-priority RPCs, by running:</para>
1479 $ lctl set_param ost.OSS.ost_io.nrs_orr_offset_type=
1480 <replaceable>reg_offset_type|hp_offset_type</replaceable>:
1481 <replaceable>physical|logical</replaceable>
1483 <para>For example, to set the offset type for high-priority RPCs to
1484 physical disk offsets, run:</para>
1486 $ lctl set_param ost.OSS.ost_io.nrs_orr_offset_type=hp_offset_type:physical
1487 ost.OSS.ost_io.nrs_orr_offset_type=hp_offset_type:physical
1489 <para>By using the last method, you can also set offset type for
1490 regular and high-priority RPCs to different values, in a single
1491 command invocation.</para>
1493 <para>Irrespective of the value of this tunable, only logical
1494 offsets can, and are used for ordering bulk write RPCs.</para>
1499 <literal>ost.OSS.ost_io.nrs_orr_supported</literal>
1502 <literal>ost.OSS.ost_io.nrs_orr_supported</literal> tunable determines
1503 the type of RPCs that the ORR policy will handle. To read the types
1504 of supported RPCs by the ORR policy, run:</para>
1506 $ lctl get_param ost.OSS.ost_io.nrs_orr_supported
1507 ost.OSS.ost_io.nrs_orr_supported=reg_supported:reads
1508 hp_supported=reads_and_writes
1511 <para>You can see that there is a separate supported 'RPC types'
1513 <literal>reg_supported</literal>) and high-priority (
1514 <literal>hp_supported</literal>) RPCs.</para>
1515 <para>To set the supported RPC types for the ORR policy, run:</para>
1517 $ lctl set_param ost.OSS.ost_io.nrs_orr_supported=
1518 <replaceable>reads|writes|reads_and_writes</replaceable>
1520 <para>This will set the supported RPC types for both regular and
1521 high-priority RPCs, to the indicated value.</para>
1522 <para>You can also specify a different supported 'RPC types' value
1523 for regular and high-priority RPCs, by running:</para>
1525 $ lctl set_param ost.OSS.ost_io.nrs_orr_supported=
1526 <replaceable>reg_supported|hp_supported</replaceable>:
1527 <replaceable>reads|writes|reads_and_writes</replaceable>
1529 <para>For example, to set the supported RPC types to bulk read and
1530 bulk write RPCs for regular requests, run:</para>
1533 ost.OSS.ost_io.nrs_orr_supported=reg_supported:reads_and_writes
1534 ost.OSS.ost_io.nrs_orr_supported=reg_supported:reads_and_writes
1537 <para>By using the last method, you can also set the supported RPC
1538 types for regular and high-priority RPC to different values, in a
1539 single command invocation.</para>
1546 <primary>tuning</primary>
1547 <secondary>Network Request Scheduler (NRS) Tuning</secondary>
1548 <tertiary>Target-based round-robin (TRR) policy</tertiary>
1549 </indexterm>Target-based Round-Robin (TRR) policy</title>
1550 <para>The target-based round-robin (TRR) policy performs batched
1551 round-robin scheduling of brw RPCs, with each batch consisting of RPCs
1552 that pertain to the same OST, as identified by its OST index.</para>
1553 <para>The TRR policy is identical to the object-based round-robin (ORR)
1554 policy, apart from using the brw RPC's target OST index instead of the
1555 backend-fs object's OST FID, for determining the RPC scheduling order.
1556 The goals of TRR are effectively the same as for ORR, and it uses the
1557 following tunables to adjust its behaviour:</para>
1561 <literal>ost.OSS.ost_io.nrs_trr_quantum</literal>
1563 <para>The purpose of this tunable is exactly the same as for the
1564 <literal>ost.OSS.ost_io.nrs_orr_quantum</literal> tunable for the ORR
1565 policy, and you can use it in exactly the same way.</para>
1569 <literal>ost.OSS.ost_io.nrs_trr_offset_type</literal>
1571 <para>The purpose of this tunable is exactly the same as for the
1572 <literal>ost.OSS.ost_io.nrs_orr_offset_type</literal> tunable for the
1573 ORR policy, and you can use it in exactly the same way.</para>
1577 <literal>ost.OSS.ost_io.nrs_trr_supported</literal>
1579 <para>The purpose of this tunable is exactly the same as for the
1580 <literal>ost.OSS.ost_io.nrs_orr_supported</literal> tunable for the
1581 ORR policy, and you can use it in exactly the sme way.</para>
1585 <section xml:id="dbdoclet.tbftuning" condition='l26'>
1588 <primary>tuning</primary>
1589 <secondary>Network Request Scheduler (NRS) Tuning</secondary>
1590 <tertiary>Token Bucket Filter (TBF) policy</tertiary>
1591 </indexterm>Token Bucket Filter (TBF) policy</title>
1592 <para>The TBF (Token Bucket Filter) is a Lustre NRS policy which enables
1593 Lustre services to enforce the RPC rate limit on clients/jobs for QoS
1594 (Quality of Service) purposes.</para>
1596 <title>The internal structure of TBF policy</title>
1599 <imagedata scalefit="1" width="100%"
1600 fileref="figures/TBF_policy.svg" />
1603 <phrase>The internal structure of TBF policy</phrase>
1607 <para>When a RPC request arrives, TBF policy puts it to a waiting queue
1608 according to its classification. The classification of RPC requests is
1609 based on either NID or JobID of the RPC according to the configure of
1610 TBF. TBF policy maintains multiple queues in the system, one queue for
1611 each category in the classification of RPC requests. The requests waits
1612 for tokens in the FIFO queue before they have been handled so as to keep
1613 the RPC rates under the limits.</para>
1614 <para>When Lustre services are too busy to handle all of the requests in
1615 time, all of the specified rates of the queues will not be satisfied.
1616 Nothing bad will happen except some of the RPC rates are slower than
1617 configured. In this case, the queue with higher rate will have an
1618 advantage over the queues with lower rates, but none of them will be
1620 <para>To manage the RPC rate of queues, we don't need to set the rate of
1621 each queue manually. Instead, we define rules which TBF policy matches to
1622 determine RPC rate limits. All of the defined rules are organized as an
1623 ordered list. Whenever a queue is newly created, it goes though the rule
1624 list and takes the first matched rule as its rule, so that the queue
1625 knows its RPC token rate. A rule can be added to or removed from the list
1626 at run time. Whenever the list of rules is changed, the queues will
1627 update their matched rules.</para>
1628 <section remap="h4">
1629 <title>Enable TBF policy</title>
1630 <para>Command:</para>
1631 <screen>lctl set_param ost.OSS.ost_io.nrs_policies="tbf <<replaceable>policy</replaceable>>"
1633 <para>For now, the RPCs can be classified into the different types
1634 according to their NID, JOBID, OPCode and UID/GID. When enabling TBF
1635 policy, you can specify one of the types, or just use "tbf" to enable
1636 all of them to do a fine-grained RPC requests classification.</para>
1637 <para>Example:</para>
1638 <screen>$ lctl set_param ost.OSS.ost_io.nrs_policies="tbf"
1639 $ lctl set_param ost.OSS.ost_io.nrs_policies="tbf nid"
1640 $ lctl set_param ost.OSS.ost_io.nrs_policies="tbf jobid"
1641 $ lctl set_param ost.OSS.ost_io.nrs_policies="tbf opcode"
1642 $ lctl set_param ost.OSS.ost_io.nrs_policies="tbf uid"
1643 $ lctl set_param ost.OSS.ost_io.nrs_policies="tbf gid"</screen>
1645 <section remap="h4">
1646 <title>Start a TBF rule</title>
1647 <para>The TBF rule is defined in the parameter
1648 <literal>ost.OSS.ost_io.nrs_tbf_rule</literal>.</para>
1649 <para>Command:</para>
1650 <screen>lctl set_param x.x.x.nrs_tbf_rule=
1651 "[reg|hp] start <replaceable>rule_name</replaceable> <replaceable>arguments</replaceable>..."
1653 <para>'<replaceable>rule_name</replaceable>' is a string of the TBF
1654 policy rule's name and '<replaceable>arguments</replaceable>' is a
1655 string to specify the detailed rule according to the different types.
1658 <para>Next, the different types of TBF policies will be described.</para>
1660 <para><emphasis role="bold">NID based TBF policy</emphasis></para>
1661 <para>Command:</para>
1662 <screen>lctl set_param x.x.x.nrs_tbf_rule=
1663 "[reg|hp] start <replaceable>rule_name</replaceable> nid={<replaceable>nidlist</replaceable>} rate=<replaceable>rate</replaceable>"
1665 <para>'<replaceable>nidlist</replaceable>' uses the same format
1666 as configuring LNET route. '<replaceable>rate</replaceable>' is
1667 the (upper limit) RPC rate of the rule.</para>
1668 <para>Example:</para>
1669 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1670 "start other_clients nid={192.168.*.*@tcp} rate=50"
1671 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1672 "start computes nid={192.168.1.[2-128]@tcp} rate=500"
1673 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1674 "start loginnode nid={192.168.1.1@tcp} rate=100"</screen>
1675 <para>In this example, the rate of processing RPC requests from
1676 compute nodes is at most 5x as fast as those from login nodes.
1677 The output of <literal>ost.OSS.ost_io.nrs_tbf_rule</literal> is
1679 <screen>lctl get_param ost.OSS.ost_io.nrs_tbf_rule
1680 ost.OSS.ost_io.nrs_tbf_rule=
1683 loginnode {192.168.1.1@tcp} 100, ref 0
1684 computes {192.168.1.[2-128]@tcp} 500, ref 0
1685 other_clients {192.168.*.*@tcp} 50, ref 0
1686 default {*} 10000, ref 0
1687 high_priority_requests:
1689 loginnode {192.168.1.1@tcp} 100, ref 0
1690 computes {192.168.1.[2-128]@tcp} 500, ref 0
1691 other_clients {192.168.*.*@tcp} 50, ref 0
1692 default {*} 10000, ref 0</screen>
1693 <para>Also, the rule can be written in <literal>reg</literal> and
1694 <literal>hp</literal> formats:</para>
1695 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1696 "reg start loginnode nid={192.168.1.1@tcp} rate=100"
1697 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1698 "hp start loginnode nid={192.168.1.1@tcp} rate=100"</screen>
1701 <para><emphasis role="bold">JobID based TBF policy</emphasis></para>
1702 <para>For the JobID, please see
1703 <xref xmlns:xlink="http://www.w3.org/1999/xlink"
1704 linkend="dbdoclet.jobstats" /> for more details.</para>
1705 <para>Command:</para>
1706 <screen>lctl set_param x.x.x.nrs_tbf_rule=
1707 "[reg|hp] start <replaceable>rule_name</replaceable> jobid={<replaceable>jobid_list</replaceable>} rate=<replaceable>rate</replaceable>"
1709 <para>Wildcard is supported in
1710 {<replaceable>jobid_list</replaceable>}.</para>
1711 <para>Example:</para>
1712 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1713 "start iozone_user jobid={iozone.500} rate=100"
1714 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1715 "start dd_user jobid={dd.*} rate=50"
1716 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1717 "start user1 jobid={*.600} rate=10"
1718 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1719 "start user2 jobid={io*.10* *.500} rate=200"</screen>
1720 <para>Also, the rule can be written in <literal>reg</literal> and
1721 <literal>hp</literal> formats:</para>
1722 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1723 "hp start iozone_user1 jobid={iozone.500} rate=100"
1724 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1725 "reg start iozone_user1 jobid={iozone.500} rate=100"</screen>
1728 <para><emphasis role="bold">Opcode based TBF policy</emphasis></para>
1729 <para>Command:</para>
1730 <screen>$ lctl set_param x.x.x.nrs_tbf_rule=
1731 "[reg|hp] start <replaceable>rule_name</replaceable> opcode={<replaceable>opcode_list</replaceable>} rate=<replaceable>rate</replaceable>"
1733 <para>Example:</para>
1734 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1735 "start user1 opcode={ost_read} rate=100"
1736 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1737 "start iozone_user1 opcode={ost_read ost_write} rate=200"</screen>
1738 <para>Also, the rule can be written in <literal>reg</literal> and
1739 <literal>hp</literal> formats:</para>
1740 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1741 "hp start iozone_user1 opcode={ost_read} rate=100"
1742 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1743 "reg start iozone_user1 opcode={ost_read} rate=100"</screen>
1746 <para><emphasis role="bold">UID/GID based TBF policy</emphasis></para>
1747 <para>Command:</para>
1748 <screen>$ lctl set_param ost.OSS.*.nrs_tbf_rule=\
1749 "[reg][hp] start <replaceable>rule_name</replaceable> uid={<replaceable>uid</replaceable>} rate=<replaceable>rate</replaceable>"
1750 $ lctl set_param ost.OSS.*.nrs_tbf_rule=\
1751 "[reg][hp] start <replaceable>rule_name</replaceable> gid={<replaceable>gid</replaceable>} rate=<replaceable>rate</replaceable>"</screen>
1752 <para>Exapmle:</para>
1753 <para>Limit the rate of RPC requests of the uid 500</para>
1754 <screen>$ lctl set_param ost.OSS.*.nrs_tbf_rule=\
1755 "start tbf_name uid={500} rate=100"</screen>
1756 <para>Limit the rate of RPC requests of the gid 500</para>
1757 <screen>$ lctl set_param ost.OSS.*.nrs_tbf_rule=\
1758 "start tbf_name gid={500} rate=100"</screen>
1759 <para>Also, you can use the following rule to control all reqs
1761 <para>Start the tbf uid QoS on MDS:</para>
1762 <screen>$ lctl set_param mds.MDS.*.nrs_policies="tbf uid"</screen>
1763 <para>Limit the rate of RPC requests of the uid 500</para>
1764 <screen>$ lctl set_param mds.MDS.*.nrs_tbf_rule=\
1765 "start tbf_name uid={500} rate=100"</screen>
1768 <para><emphasis role="bold">Policy combination</emphasis></para>
1769 <para>To support TBF rules with complex expressions of conditions,
1770 TBF classifier is extented to classify RPC in a more fine-grained
1771 way. This feature supports logical conditional conjunction and
1772 disjunction operations among different types.
1774 "&" represents the conditional conjunction and
1775 "," represents the conditional disjunction.</para>
1776 <para>Example:</para>
1777 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1778 "start comp_rule opcode={ost_write}&jobid={dd.0},\
1779 nid={192.168.1.[1-128]@tcp 0@lo} rate=100"</screen>
1780 <para>In this example, those RPCs whose <literal>opcode</literal> is
1781 ost_write and <literal>jobid</literal> is dd.0, or
1782 <literal>nid</literal> satisfies the condition of
1783 {192.168.1.[1-128]@tcp 0@lo} will be processed at the rate of 100
1785 The output of <literal>ost.OSS.ost_io.nrs_tbf_rule</literal>is like:
1787 <screen>$ lctl get_param ost.OSS.ost_io.nrs_tbf_rule
1788 ost.OSS.ost_io.nrs_tbf_rule=
1791 comp_rule opcode={ost_write}&jobid={dd.0},nid={192.168.1.[1-128]@tcp 0@lo} 100, ref 0
1792 default * 10000, ref 0
1794 comp_rule opcode={ost_write}&jobid={dd.0},nid={192.168.1.[1-128]@tcp 0@lo} 100, ref 0
1795 default * 10000, ref 0
1796 high_priority_requests:
1798 comp_rule opcode={ost_write}&jobid={dd.0},nid={192.168.1.[1-128]@tcp 0@lo} 100, ref 0
1799 default * 10000, ref 0
1801 comp_rule opcode={ost_write}&jobid={dd.0},nid={192.168.1.[1-128]@tcp 0@lo} 100, ref 0
1802 default * 10000, ref 0</screen>
1803 <para>Example:</para>
1804 <screen>$ lctl set_param ost.OSS.*.nrs_tbf_rule=\
1805 "start tbf_name uid={500}&gid={500} rate=100"</screen>
1806 <para>In this example, those RPC requests whose uid is 500 and
1807 gid is 500 will be processed at the rate of 100 req/sec.</para>
1811 <section remap="h4">
1812 <title>Change a TBF rule</title>
1813 <para>Command:</para>
1814 <screen>lctl set_param x.x.x.nrs_tbf_rule=
1815 "[reg|hp] change <replaceable>rule_name</replaceable> rate=<replaceable>rate</replaceable>"
1817 <para>Example:</para>
1818 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1819 "change loginnode rate=200"
1820 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1821 "reg change loginnode rate=200"
1822 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1823 "hp change loginnode rate=200"
1826 <section remap="h4">
1827 <title>Stop a TBF rule</title>
1828 <para>Command:</para>
1829 <screen>lctl set_param x.x.x.nrs_tbf_rule="[reg|hp] stop
1830 <replaceable>rule_name</replaceable>"</screen>
1831 <para>Example:</para>
1832 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule="stop loginnode"
1833 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule="reg stop loginnode"
1834 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule="hp stop loginnode"</screen>
1836 <section remap="h4">
1837 <title>Rule options</title>
1838 <para>To support more flexible rule conditions, the following options
1842 <para><emphasis role="bold">Reordering of TBF rules</emphasis></para>
1843 <para>By default, a newly started rule is prior to the old ones,
1844 but by specifying the argument '<literal>rank=</literal>' when
1845 inserting a new rule with "<literal>start</literal>" command,
1846 the rank of the rule can be changed. Also, it can be changed by
1847 "<literal>change</literal>" command.
1849 <para>Command:</para>
1850 <screen>lctl set_param ost.OSS.ost_io.nrs_tbf_rule=
1851 "start <replaceable>rule_name</replaceable> <replaceable>arguments</replaceable>... rank=<replaceable>obj_rule_name</replaceable>"
1852 lctl set_param ost.OSS.ost_io.nrs_tbf_rule=
1853 "change <replaceable>rule_name</replaceable> rate=<replaceable>rate</replaceable> rank=<replaceable>obj_rule_name</replaceable>"
1855 <para>By specifying the existing rule
1856 '<replaceable>obj_rule_name</replaceable>', the new rule
1857 '<replaceable>rule_name</replaceable>' will be moved to the front of
1858 '<replaceable>obj_rule_name</replaceable>'.</para>
1859 <para>Example:</para>
1860 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1861 "start computes nid={192.168.1.[2-128]@tcp} rate=500"
1862 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1863 "start user1 jobid={iozone.500 dd.500} rate=100"
1864 $ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=\
1865 "start iozone_user1 opcode={ost_read ost_write} rate=200 rank=computes"</screen>
1866 <para>In this example, rule "iozone_user1" is added to the front of
1867 rule "computes". We can see the order by the following command:
1869 <screen>$ lctl get_param ost.OSS.ost_io.nrs_tbf_rule
1870 ost.OSS.ost_io.nrs_tbf_rule=
1873 user1 jobid={iozone.500 dd.500} 100, ref 0
1874 iozone_user1 opcode={ost_read ost_write} 200, ref 0
1875 computes nid={192.168.1.[2-128]@tcp} 500, ref 0
1876 default * 10000, ref 0
1878 user1 jobid={iozone.500 dd.500} 100, ref 0
1879 iozone_user1 opcode={ost_read ost_write} 200, ref 0
1880 computes nid={192.168.1.[2-128]@tcp} 500, ref 0
1881 default * 10000, ref 0
1882 high_priority_requests:
1884 user1 jobid={iozone.500 dd.500} 100, ref 0
1885 iozone_user1 opcode={ost_read ost_write} 200, ref 0
1886 computes nid={192.168.1.[2-128]@tcp} 500, ref 0
1887 default * 10000, ref 0
1889 user1 jobid={iozone.500 dd.500} 100, ref 0
1890 iozone_user1 opcode={ost_read ost_write} 200, ref 0
1891 computes nid={192.168.1.[2-128]@tcp} 500, ref 0
1892 default * 10000, ref 0</screen>
1895 <para><emphasis role="bold">TBF realtime policies under congestion
1897 <para>During TBF evaluation, we find that when the sum of I/O
1898 bandwidth requirements for all classes exceeds the system capacity,
1899 the classes with the same rate limits get less bandwidth than if
1900 preconfigured evenly. The reason for this is the heavy load on a
1901 congested server will result in some missed deadlines for some
1902 classes. The number of the calculated tokens may be larger than 1
1903 during dequeuing. In the original implementation, all classes are
1904 equally handled to simply discard exceeding tokens.</para>
1905 <para>Thus, a Hard Token Compensation (HTC) strategy has been
1906 implemented. A class can be configured with the HTC feature by the
1907 rule it matches. This feature means that requests in this kind of
1908 class queues have high real-time requirements and that the bandwidth
1909 assignment must be satisfied as good as possible. When deadline
1910 misses happen, the class keeps the deadline unchanged and the time
1911 residue(the remainder of elapsed time divided by 1/r) is compensated
1912 to the next round. This ensures that the next idle I/O thread will
1913 always select this class to serve until all accumulated exceeding
1914 tokens are handled or there are no pending requests in the class
1916 <para>Command:</para>
1917 <para>A new command format is added to enable the realtime feature
1919 <screen>lctl set_param x.x.x.nrs_tbf_rule=\
1920 "start <replaceable>rule_name</replaceable> <replaceable>arguments</replaceable>... realtime=1</screen>
1921 <para>Example:</para>
1922 <screen>$ lctl set_param ost.OSS.ost_io.nrs_tbf_rule=
1923 "start realjob jobid={dd.0} rate=100 realtime=1</screen>
1924 <para>This example rule means the RPC requests whose JobID is dd.0
1925 will be processed at the rate of 100req/sec in realtime.</para>
1930 <section xml:id="dbdoclet.delaytuning" condition='l2A'>
1933 <primary>tuning</primary>
1934 <secondary>Network Request Scheduler (NRS) Tuning</secondary>
1935 <tertiary>Delay policy</tertiary>
1936 </indexterm>Delay policy</title>
1937 <para>The NRS Delay policy seeks to perturb the timing of request
1938 processing at the PtlRPC layer, with the goal of simulating high server
1939 load, and finding and exposing timing related problems. When this policy
1940 is active, upon arrival of a request the policy will calculate an offset,
1941 within a defined, user-configurable range, from the request arrival
1942 time, to determine a time after which the request should be handled.
1943 The request is then stored using the cfs_binheap implementation,
1944 which sorts the request according to the assigned start time.
1945 Requests are removed from the binheap for handling once their start
1946 time has been passed.</para>
1947 <para>The Delay policy can be enabled on all types of PtlRPC services,
1948 and has the following tunables that can be used to adjust its behavior:
1953 <literal>{service}.nrs_delay_min</literal>
1956 <literal>{service}.nrs_delay_min</literal> tunable controls the
1957 minimum amount of time, in seconds, that a request will be delayed by
1958 this policy. The default is 5 seconds. To read this value run:</para>
1960 lctl get_param {service}.nrs_delay_min</screen>
1961 <para>For example, to read the minimum delay set on the ost_io
1962 service, run:</para>
1964 $ lctl get_param ost.OSS.ost_io.nrs_delay_min
1965 ost.OSS.ost_io.nrs_delay_min=reg_delay_min:5
1966 hp_delay_min:5</screen>
1967 <para>To set the minimum delay in RPC processing, run:</para>
1969 lctl set_param {service}.nrs_delay_min=<replaceable>0-65535</replaceable></screen>
1970 <para>This will set the minimum delay time on a given service, for both
1971 regular and high-priority RPCs (if the PtlRPC service supports
1972 high-priority RPCs), to the indicated value.</para>
1973 <para>For example, to set the minimum delay time on the ost_io service
1976 $ lctl set_param ost.OSS.ost_io.nrs_delay_min=10
1977 ost.OSS.ost_io.nrs_delay_min=10</screen>
1978 <para>For PtlRPC services that support high-priority RPCs, to set a
1979 different minimum delay time for regular and high-priority RPCs, run:
1982 lctl set_param {service}.nrs_delay_min=<replaceable>reg_delay_min|hp_delay_min</replaceable>:<replaceable>0-65535</replaceable>
1984 <para>For example, to set the minimum delay time on the ost_io service
1985 for high-priority RPCs to 3, run:</para>
1987 $ lctl set_param ost.OSS.ost_io.nrs_delay_min=hp_delay_min:3
1988 ost.OSS.ost_io.nrs_delay_min=hp_delay_min:3</screen>
1989 <para>Note, in all cases the minimum delay time cannot exceed the
1990 maximum delay time.</para>
1994 <literal>{service}.nrs_delay_max</literal>
1997 <literal>{service}.nrs_delay_max</literal> tunable controls the
1998 maximum amount of time, in seconds, that a request will be delayed by
1999 this policy. The default is 300 seconds. To read this value run:
2001 <screen>lctl get_param {service}.nrs_delay_max</screen>
2002 <para>For example, to read the maximum delay set on the ost_io
2003 service, run:</para>
2005 $ lctl get_param ost.OSS.ost_io.nrs_delay_max
2006 ost.OSS.ost_io.nrs_delay_max=reg_delay_max:300
2007 hp_delay_max:300</screen>
2008 <para>To set the maximum delay in RPC processing, run:</para>
2009 <screen>lctl set_param {service}.nrs_delay_max=<replaceable>0-65535</replaceable>
2011 <para>This will set the maximum delay time on a given service, for both
2012 regular and high-priority RPCs (if the PtlRPC service supports
2013 high-priority RPCs), to the indicated value.</para>
2014 <para>For example, to set the maximum delay time on the ost_io service
2017 $ lctl set_param ost.OSS.ost_io.nrs_delay_max=60
2018 ost.OSS.ost_io.nrs_delay_max=60</screen>
2019 <para>For PtlRPC services that support high-priority RPCs, to set a
2020 different maximum delay time for regular and high-priority RPCs, run:
2022 <screen>lctl set_param {service}.nrs_delay_max=<replaceable>reg_delay_max|hp_delay_max</replaceable>:<replaceable>0-65535</replaceable></screen>
2023 <para>For example, to set the maximum delay time on the ost_io service
2024 for high-priority RPCs to 30, run:</para>
2026 $ lctl set_param ost.OSS.ost_io.nrs_delay_max=hp_delay_max:30
2027 ost.OSS.ost_io.nrs_delay_max=hp_delay_max:30</screen>
2028 <para>Note, in all cases the maximum delay time cannot be less than the
2029 minimum delay time.</para>
2033 <literal>{service}.nrs_delay_pct</literal>
2036 <literal>{service}.nrs_delay_pct</literal> tunable controls the
2037 percentage of requests that will be delayed by this policy. The
2038 default is 100. Note, when a request is not selected for handling by
2039 the delay policy due to this variable then the request will be handled
2040 by whatever fallback policy is defined for that service. If no other
2041 fallback policy is defined then the request will be handled by the
2042 FIFO policy. To read this value run:</para>
2043 <screen>lctl get_param {service}.nrs_delay_pct</screen>
2044 <para>For example, to read the percentage of requests being delayed on
2045 the ost_io service, run:</para>
2047 $ lctl get_param ost.OSS.ost_io.nrs_delay_pct
2048 ost.OSS.ost_io.nrs_delay_pct=reg_delay_pct:100
2049 hp_delay_pct:100</screen>
2050 <para>To set the percentage of delayed requests, run:</para>
2052 lctl set_param {service}.nrs_delay_pct=<replaceable>0-100</replaceable></screen>
2053 <para>This will set the percentage of requests delayed on a given
2054 service, for both regular and high-priority RPCs (if the PtlRPC service
2055 supports high-priority RPCs), to the indicated value.</para>
2056 <para>For example, to set the percentage of delayed requests on the
2057 ost_io service to 50, run:</para>
2059 $ lctl set_param ost.OSS.ost_io.nrs_delay_pct=50
2060 ost.OSS.ost_io.nrs_delay_pct=50
2062 <para>For PtlRPC services that support high-priority RPCs, to set a
2063 different delay percentage for regular and high-priority RPCs, run:
2065 <screen>lctl set_param {service}.nrs_delay_pct=<replaceable>reg_delay_pct|hp_delay_pct</replaceable>:<replaceable>0-100</replaceable>
2067 <para>For example, to set the percentage of delayed requests on the
2068 ost_io service for high-priority RPCs to 5, run:</para>
2069 <screen>$ lctl set_param ost.OSS.ost_io.nrs_delay_pct=hp_delay_pct:5
2070 ost.OSS.ost_io.nrs_delay_pct=hp_delay_pct:5
2076 <section xml:id="dbdoclet.50438272_25884">
2079 <primary>tuning</primary>
2080 <secondary>lockless I/O</secondary>
2081 </indexterm>Lockless I/O Tunables</title>
2082 <para>The lockless I/O tunable feature allows servers to ask clients to do
2083 lockless I/O (the server does the locking on behalf of clients) for
2084 contended files to avoid lock ping-pong.</para>
2085 <para>The lockless I/O patch introduces these tunables:</para>
2089 <emphasis role="bold">OST-side:</emphasis>
2092 ldlm.namespaces.filter-<replaceable>fsname</replaceable>-*.
2095 <literal>contended_locks</literal>- If the number of lock conflicts in
2096 the scan of granted and waiting queues at contended_locks is exceeded,
2097 the resource is considered to be contended.</para>
2099 <literal>contention_seconds</literal>- The resource keeps itself in a
2100 contended state as set in the parameter.</para>
2102 <literal>max_nolock_bytes</literal>- Server-side locking set only for
2103 requests less than the blocks set in the
2104 <literal>max_nolock_bytes</literal> parameter. If this tunable is
2105 set to zero (0), it disables server-side locking for read/write
2110 <emphasis role="bold">Client-side:</emphasis>
2113 /proc/fs/lustre/llite/lustre-*
2116 <literal>contention_seconds</literal>-
2117 <literal>llite</literal> inode remembers its contended state for the
2118 time specified in this parameter.</para>
2122 <emphasis role="bold">Client-side statistics:</emphasis>
2125 <literal>/proc/fs/lustre/llite/lustre-*/stats</literal> file has new
2126 rows for lockless I/O statistics.</para>
2128 <literal>lockless_read_bytes</literal> and
2129 <literal>lockless_write_bytes</literal>- To count the total bytes read
2130 or written, the client makes its own decisions based on the request
2131 size. The client does not communicate with the server if the request
2132 size is smaller than the
2133 <literal>min_nolock_size</literal>, without acquiring locks by the
2138 <section condition="l29">
2141 <primary>tuning</primary>
2142 <secondary>with lfs ladvise</secondary>
2144 Server-Side Advice and Hinting
2146 <section><title>Overview</title>
2147 <para>Use the <literal>lfs ladvise</literal> command to give file access
2148 advices or hints to servers.</para>
2149 <screen>lfs ladvise [--advice|-a ADVICE ] [--background|-b]
2150 [--start|-s START[kMGT]]
2151 {[--end|-e END[kMGT]] | [--length|-l LENGTH[kMGT]]}
2152 <emphasis>file</emphasis> ...
2155 <informaltable frame="all">
2157 <colspec colname="c1" colwidth="50*"/>
2158 <colspec colname="c2" colwidth="50*"/>
2162 <para><emphasis role="bold">Option</emphasis></para>
2165 <para><emphasis role="bold">Description</emphasis></para>
2172 <para><literal>-a</literal>, <literal>--advice=</literal>
2173 <literal>ADVICE</literal></para>
2176 <para>Give advice or hint of type <literal>ADVICE</literal>.
2177 Advice types are:</para>
2178 <para><literal>willread</literal> to prefetch data into server
2180 <para><literal>dontneed</literal> to cleanup data cache on
2182 <para><literal>lockahead</literal> Request an LDLM extent lock
2183 of the given mode on the given byte range </para>
2184 <para><literal>noexpand</literal> Disable extent lock expansion
2185 behavior for I/O to this file descriptor</para>
2190 <para><literal>-b</literal>, <literal>--background</literal>
2194 <para>Enable the advices to be sent and handled asynchronously.
2200 <para><literal>-s</literal>, <literal>--start=</literal>
2201 <literal>START_OFFSET</literal></para>
2204 <para>File range starts from <literal>START_OFFSET</literal>
2210 <para><literal>-e</literal>, <literal>--end=</literal>
2211 <literal>END_OFFSET</literal></para>
2214 <para>File range ends at (not including)
2215 <literal>END_OFFSET</literal>. This option may not be
2216 specified at the same time as the <literal>-l</literal>
2222 <para><literal>-l</literal>, <literal>--length=</literal>
2223 <literal>LENGTH</literal></para>
2226 <para>File range has length of <literal>LENGTH</literal>.
2227 This option may not be specified at the same time as the
2228 <literal>-e</literal> option.</para>
2233 <para><literal>-m</literal>, <literal>--mode=</literal>
2234 <literal>MODE</literal></para>
2237 <para>Lockahead request mode <literal>{READ,WRITE}</literal>.
2238 Request a lock with this mode.</para>
2245 <para>Typically, <literal>lfs ladvise</literal> forwards the advice to
2246 Lustre servers without guaranteeing when and what servers will react to
2247 the advice. Actions may or may not triggered when the advices are
2248 recieved, depending on the type of the advice, as well as the real-time
2249 decision of the affected server-side components.</para>
2250 <para>A typical usage of ladvise is to enable applications and users with
2251 external knowledge to intervene in server-side cache management. For
2252 example, if a bunch of different clients are doing small random reads of a
2253 file, prefetching pages into OSS cache with big linear reads before the
2254 random IO is a net benefit. Fetching that data into each client cache with
2255 fadvise() may not be, due to much more data being sent to the client.
2258 <literal>ladvise lockahead</literal> is different in that it attempts to
2259 control LDLM locking behavior by explicitly requesting LDLM locks in
2260 advance of use. This does not directly affect caching behavior, instead
2261 it is used in special cases to avoid pathological results (lock exchange)
2262 from the normal LDLM locking behavior.
2265 Note that the <literal>noexpand</literal> advice works on a specific
2266 file descriptor, so using it via lfs has no effect. It must be used
2267 on a particular file descriptor which is used for i/o to have any effect.
2269 <para>The main difference between the Linux <literal>fadvise()</literal>
2270 system call and <literal>lfs ladvise</literal> is that
2271 <literal>fadvise()</literal> is only a client side mechanism that does
2272 not pass the advice to the filesystem, while <literal>ladvise</literal>
2273 can send advices or hints to the Lustre server side.</para>
2275 <section><title>Examples</title>
2276 <para>The following example gives the OST(s) holding the first 1GB of
2277 <literal>/mnt/lustre/file1</literal>a hint that the first 1GB of the
2278 file will be read soon.</para>
2279 <screen>client1$ lfs ladvise -a willread -s 0 -e 1048576000 /mnt/lustre/file1
2281 <para>The following example gives the OST(s) holding the first 1GB of
2282 <literal>/mnt/lustre/file1</literal> a hint that the first 1GB of file
2283 will not be read in the near future, thus the OST(s) could clear the
2284 cache of the file in the memory.</para>
2285 <screen>client1$ lfs ladvise -a dontneed -s 0 -e 1048576000 /mnt/lustre/file1
2287 <para>The following example requests an LDLM read lock on the first
2288 1 MiB of <literal>/mnt/lustre/file1</literal>. This will attempt to
2289 request a lock from the OST holding that region of the file.</para>
2290 <screen>client1$ lfs ladvise -a lockahead -m READ -s 0 -e 1M /mnt/lustre/file1
2292 <para>The following example requests an LDLM write lock on
2293 [3 MiB, 10 MiB] of <literal>/mnt/lustre/file1</literal>. This will
2294 attempt to request a lock from the OST holding that region of the
2296 <screen>client1$ lfs ladvise -a lockahead -m WRITE -s 3M -e 10M /mnt/lustre/file1
2300 <section condition="l29">
2303 <primary>tuning</primary>
2304 <secondary>Large Bulk IO</secondary>
2306 Large Bulk IO (16MB RPC)
2308 <section><title>Overview</title>
2309 <para>Beginning with Lustre 2.9, Lustre is extended to support RPCs up
2310 to 16MB in size. By enabling a larger RPC size, fewer RPCs will be
2311 required to transfer the same amount of data between clients and
2312 servers. With a larger RPC size, the OSS can submit more data to the
2313 underlying disks at once, therefore it can produce larger disk I/Os
2314 to fully utilize the increasing bandwidth of disks.</para>
2315 <para>At client connection time, clients will negotiate with
2316 servers what the maximum RPC size it is possible to use, but the
2317 client can always send RPCs smaller than this maximum.</para>
2318 <para>The parameter <literal>brw_size</literal> is used on the OST
2319 to tell the client the maximum (preferred) IO size. All clients that
2320 talk to this target should never send an RPC greater than this size.
2321 Clients can individually set a smaller RPC size limit via the
2322 <literal>osc.*.max_pages_per_rpc</literal> tunable.
2325 <para>The smallest <literal>brw_size</literal> that can be set for
2326 ZFS OSTs is the <literal>recordsize</literal> of that dataset. This
2327 ensures that the client can always write a full ZFS file block if it
2328 has enough dirty data, and does not otherwise force it to do read-
2329 modify-write operations for every RPC.
2333 <section><title>Usage</title>
2334 <para>In order to enable a larger RPC size,
2335 <literal>brw_size</literal> must be changed to an IO size value up to
2336 16MB. To temporarily change <literal>brw_size</literal>, the
2337 following command should be run on the OSS:</para>
2338 <screen>oss# lctl set_param obdfilter.<replaceable>fsname</replaceable>-OST*.brw_size=16</screen>
2339 <para>To persistently change <literal>brw_size</literal>, the
2340 following command should be run:</para>
2341 <screen>oss# lctl set_param -P obdfilter.<replaceable>fsname</replaceable>-OST*.brw_size=16</screen>
2342 <para>When a client connects to an OST target, it will fetch
2343 <literal>brw_size</literal> from the target and pick the maximum value
2344 of <literal>brw_size</literal> and its local setting for
2345 <literal>max_pages_per_rpc</literal> as the actual RPC size.
2346 Therefore, the <literal>max_pages_per_rpc</literal> on the client side
2347 would have to be set to 16M, or 4096 if the PAGESIZE is 4KB, to enable
2348 a 16MB RPC. To temporarily make the change, the following command
2349 should be run on the client to set
2350 <literal>max_pages_per_rpc</literal>:</para>
2351 <screen>client$ lctl set_param osc.<replaceable>fsname</replaceable>-OST*.max_pages_per_rpc=16M</screen>
2352 <para>To persistently make this change, the following command should
2354 <screen>client$ lctl set_param -P obdfilter.<replaceable>fsname</replaceable>-OST*.osc.max_pages_per_rpc=16M</screen>
2355 <caution><para>The <literal>brw_size</literal> of an OST can be
2356 changed on the fly. However, clients have to be remounted to
2357 renegotiate the new maximum RPC size.</para></caution>
2360 <section xml:id="dbdoclet.50438272_80545">
2363 <primary>tuning</primary>
2364 <secondary>for small files</secondary>
2365 </indexterm>Improving Lustre I/O Performance for Small Files</title>
2366 <para>An environment where an application writes small file chunks from
2367 many clients to a single file can result in poor I/O performance. To
2368 improve the performance of the Lustre file system with small files:</para>
2371 <para>Have the application aggregate writes some amount before
2372 submitting them to the Lustre file system. By default, the Lustre
2373 software enforces POSIX coherency semantics, so it results in lock
2374 ping-pong between client nodes if they are all writing to the same
2375 file at one time.</para>
2376 <para>Using MPI-IO Collective Write functionality in
2377 the Lustre ADIO driver is one way to achieve this in a straight
2378 forward manner if the application is already using MPI-IO.</para>
2381 <para>Have the application do 4kB
2382 <literal>O_DIRECT</literal> sized I/O to the file and disable locking
2383 on the output file. This avoids partial-page IO submissions and, by
2384 disabling locking, you avoid contention between clients.</para>
2387 <para>Have the application write contiguous data.</para>
2390 <para>Add more disks or use SSD disks for the OSTs. This dramatically
2391 improves the IOPS rate. Consider creating larger OSTs rather than many
2392 smaller OSTs due to less overhead (journal, connections, etc).</para>
2395 <para>Use RAID-1+0 OSTs instead of RAID-5/6. There is RAID parity
2396 overhead for writing small chunks of data to disk.</para>
2400 <section xml:id="dbdoclet.50438272_45406">
2403 <primary>tuning</primary>
2404 <secondary>write performance</secondary>
2405 </indexterm>Understanding Why Write Performance is Better Than Read
2407 <para>Typically, the performance of write operations on a Lustre cluster is
2408 better than read operations. When doing writes, all clients are sending
2409 write RPCs asynchronously. The RPCs are allocated, and written to disk in
2410 the order they arrive. In many cases, this allows the back-end storage to
2411 aggregate writes efficiently.</para>
2412 <para>In the case of read operations, the reads from clients may come in a
2413 different order and need a lot of seeking to get read from the disk. This
2414 noticeably hampers the read throughput.</para>
2415 <para>Currently, there is no readahead on the OSTs themselves, though the
2416 clients do readahead. If there are lots of clients doing reads it would not
2417 be possible to do any readahead in any case because of memory consumption
2418 (consider that even a single RPC (1 MB) readahead for 1000 clients would
2419 consume 1 GB of RAM).</para>
2420 <para>For file systems that use socklnd (TCP, Ethernet) as interconnect,
2421 there is also additional CPU overhead because the client cannot receive
2422 data without copying it from the network buffers. In the write case, the
2423 client CAN send data without the additional data copy. This means that the
2424 client is more likely to become CPU-bound during reads than writes.</para>
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