Update a comment to reflect new taskq internals

[mirror_zfs.git] / module / spl / spl-taskq.c

diff --git a/module/spl/spl-taskq.c b/module/spl/spl-taskq.c
index 0b3b3a1315d3e9a148f85a411ff48f8de02f4245..67a8345725d5352e4d51a4688fdccb4314127789 100644 (file)
--- a/module/spl/spl-taskq.c
+++ b/module/spl/spl-taskq.c
@@ -156,19 +156,22 @@ task_done(taskq_t *tq, taskq_ent_t *t)
  * monotonically increasing taskqid and added to the tail of the pending
  * list.  As worker threads become available the tasks are removed from
  * the head of the pending or priority list, giving preference to the
- * priority list.  The tasks are then added to the work list, preserving
- * the ordering by taskqid.  Finally, as tasks complete they are removed
- * from the work list.  This means that the pending and work lists are
- * always kept sorted by taskqid.  Thus the lowest outstanding
- * incomplete taskqid can be determined simply by checking the min
- * taskqid for each head item on the pending, priority, and work list.
- * This value is stored in tq->tq_lowest_id and only updated to the new
- * lowest id when the previous lowest id completes.  All taskqids lower
- * than tq->tq_lowest_id must have completed.  It is also possible
- * larger taskqid's have completed because they may be processed in
- * parallel by several worker threads.  However, this is not a problem
- * because the behavior of taskq_wait_id() is to block until all
- * previously submitted taskqid's have completed.
+ * priority list.  The tasks are then removed from their respective
+ * list, and the taskq_thread servicing the task is added to the active
+ * list, preserving the order using the serviced task's taskqid.
+ * Finally, as tasks complete the taskq_thread servicing the task is
+ * removed from the active list.  This means that the pending task and
+ * active taskq_thread lists are always kept sorted by taskqid. Thus the
+ * lowest outstanding incomplete taskqid can be determined simply by
+ * checking the min taskqid for each head item on the pending, priority,
+ * and active taskq_thread list. This value is stored in
+ * tq->tq_lowest_id and only updated to the new lowest id when the
+ * previous lowest id completes.  All taskqids lower than
+ * tq->tq_lowest_id must have completed.  It is also possible larger
+ * taskqid's have completed because they may be processed in parallel by
+ * several worker threads.  However, this is not a problem because the
+ * behavior of taskq_wait_id() is to block until all previously
+ * submitted taskqid's have completed.
  *
  * XXX: Taskqid_t wrapping is not handled.  However, taskqid_t's are
  * 64-bit values so even if a taskq is processing 2^24 (16,777,216)