+ * We will have percpt request history list for ptlrpc service in upcoming
+ * patches because we don't want to be serialized by current per-service
+ * history operations. So we require history ID can (somehow) show arriving
+ * order w/o grabbing global lock, and user can sort them in userspace.
+ *
+ * This is how we generate history ID for ptlrpc_request:
+ * ----------------------------------------------------
+ * | 32 bits | 16 bits | (16 - X)bits | X bits |
+ * ----------------------------------------------------
+ * | seconds | usec / 16 | sequence | CPT id |
+ * ----------------------------------------------------
+ *
+ * it might not be precise but should be good enough.
+ */
+
+#define REQS_CPT_BITS(svcpt) ((svcpt)->scp_service->srv_cpt_bits)
+
+#define REQS_SEC_SHIFT 32
+#define REQS_USEC_SHIFT 16
+#define REQS_SEQ_SHIFT(svcpt) REQS_CPT_BITS(svcpt)
+
+static void ptlrpc_req_add_history(struct ptlrpc_service_part *svcpt,
+ struct ptlrpc_request *req)
+{
+ __u64 sec = req->rq_arrival_time.tv_sec;
+ __u32 usec = req->rq_arrival_time.tv_usec >> 4; /* usec / 16 */
+ __u64 new_seq;
+
+ /* set sequence ID for request and add it to history list,
+ * it must be called with hold svcpt::scp_lock */
+
+ new_seq = (sec << REQS_SEC_SHIFT) |
+ (usec << REQS_USEC_SHIFT) | svcpt->scp_cpt;
+ if (new_seq > svcpt->scp_hist_seq) {
+ /* This handles the initial case of scp_hist_seq == 0 or
+ * we just jumped into a new time window */
+ svcpt->scp_hist_seq = new_seq;
+ } else {
+ LASSERT(REQS_SEQ_SHIFT(svcpt) < REQS_USEC_SHIFT);
+ /* NB: increase sequence number in current usec bucket,
+ * however, it's possible that we used up all bits for
+ * sequence and jumped into the next usec bucket (future time),
+ * then we hope there will be less RPCs per bucket at some
+ * point, and sequence will catch up again */
+ svcpt->scp_hist_seq += (1U << REQS_SEQ_SHIFT(svcpt));
+ new_seq = svcpt->scp_hist_seq;
+ }
+
+ req->rq_history_seq = new_seq;
+
+ cfs_list_add_tail(&req->rq_history_list, &svcpt->scp_hist_reqs);
+}
+
+/*