Another set of vdev queue optimizations.

Switch FIFO queues (SYNC/TRIM) and active queue of vdev queue from
time-sorted AVL-trees to simple lists.  AVL-trees are too expensive
for such a simple task.  To change I/O priority without searching
through the trees, add io_queue_state field to struct zio.

To not check number of queued I/Os for each priority add vq_cqueued
bitmap to struct vdev_queue.  Update it when adding/removing I/Os.
Make vq_cactive a separate array instead of struct vdev_queue_class
member.  Together those allow to avoid lots of cache misses when
looking for work in vdev_queue_class_to_issue().

Introduce deadline of ~0.5s for LBA-sorted queues.  Before this I
saw some I/Os waiting in a queue for up to 8 seconds and possibly
more due to starvation.  With this change I no longer see it.  I
had to slightly more complicate the comparison function, but since
it uses all the same cache lines the difference is minimal.  For a
sequential I/Os the new code in vdev_queue_io_to_issue() actually
often uses more simple avl_first(), falling back to avl_find() and
avl_nearest() only when needed.

Arrange members in struct zio to access only one cache line when
searching through vdev queues.  While there, remove io_alloc_node,
reusing the io_queue_node instead.  Those two are never used same
time.

Remove zfs_vdev_aggregate_trim parameter.  It was disabled for 4
years since implemented, while still wasted time maintaining the
offset-sorted tree of TRIM requests.  Just remove the tree.

Remove locking from txg_all_lists_empty().  It is racy by design,
while 2 pair of locks/unlocks take noticeable time under the vdev
queue lock.

With these changes in my tests with volblocksize=4KB I measure vdev
queue lock spin time reduction by 50% on read and 75% on write.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes #14925 

1 files changed, 0 insertions, 6 deletions

diff --git a/man/man4/zfs.4 b/man/man4/zfs.4
index 5fbd9d7db..04bbbc5fd 100644
--- a/man/man4/zfs.4
+++ b/man/man4/zfs.4
@@ -2016,12 +2016,6 @@ Historical statistics for this many latest TXGs will be available in
 Flush dirty data to disk at least every this many seconds (maximum TXG
 duration).
 .
-.It Sy zfs_vdev_aggregate_trim Ns = Ns Sy 0 Ns | Ns 1 Pq uint
-Allow TRIM I/O operations to be aggregated.
-This is normally not helpful because the extents to be trimmed
-will have been already been aggregated by the metaslab.
-This option is provided for debugging and performance analysis.
-.
 .It Sy zfs_vdev_aggregation_limit Ns = Ns Sy 1048576 Ns B Po 1 MiB Pc Pq uint
 Max vdev I/O aggregation size.
 .