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Move gethrtime() calls out of vdev queue lock

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This dramatically reduces the lock contention on systems with slower
(non-TSC) timecounters.  With TSC the difference is minimal, but since
this lock is pretty congested, any improvement counts.  Plus I don't
see any reason to do it under the lock other than the latency of the
lock itself, which this change actually reduces.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Closes #12281
This commit is contained in:
Alexander Motin 2021-07-06 17:38:00 -04:00 committed by Tony Hutter
parent dab147d65a
commit 41b33dce44
1 changed files with 5 additions and 6 deletions
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11
module/zfs/vdev_queue.c
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@ -912,9 +912,9 @@ vdev_queue_io(zio_t *zio)
}
zio->io_flags |= ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE;
zio->io_timestamp = gethrtime();
mutex_enter(&vq->vq_lock);
zio->io_timestamp = gethrtime();
vdev_queue_io_add(vq, zio);
nio = vdev_queue_io_to_issue(vq);
mutex_exit(&vq->vq_lock);
@ -936,14 +936,13 @@ vdev_queue_io_done(zio_t *zio)
vdev_queue_t *vq = &zio->io_vd->vdev_queue;
zio_t *nio;
hrtime_t now = gethrtime();
vq->vq_io_complete_ts = now;
vq->vq_io_delta_ts = zio->io_delta = now - zio->io_timestamp;
mutex_enter(&vq->vq_lock);
vdev_queue_pending_remove(vq, zio);
zio->io_delta = gethrtime() - zio->io_timestamp;
vq->vq_io_complete_ts = gethrtime();
vq->vq_io_delta_ts = vq->vq_io_complete_ts - zio->io_timestamp;
while ((nio = vdev_queue_io_to_issue(vq)) != NULL) {
mutex_exit(&vq->vq_lock);
if (nio->io_done == vdev_queue_agg_io_done) {