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Support re-prioritizing asynchronous prefetches

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When sequential scrubs were merged, all calls to arc_read()
(including prefetch IOs) were given ZIO_PRIORITY_ASYNC_READ.
Unfortunately, this behaves badly with an existing issue where
prefetch IOs cannot be re-prioritized after the issue. The
result is that synchronous reads end up in the same vdev_queue
as the scrub IOs and can have (in some workloads) multiple
seconds of latency.

This patch incorporates 2 changes. The first ensures that all
scrub IOs are given ZIO_PRIORITY_SCRUB to allow the vdev_queue
code to differentiate between these I/Os and user prefetches.
Second, this patch introduces zio_change_priority() to provide
the missing capability to upgrade a zio's priority.

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #6921 
Closes #6926
This commit is contained in:
Tom Caputi
2017-12-21 12:13:06 -05:00
committed by Brian Behlendorf
parent 993669a7bf
commit a8b2e30685
11 changed files with 124 additions and 43 deletions
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module/zfs/vdev_queue.c
+42
View File
@@ -803,6 +803,48 @@ vdev_queue_io_done(zio_t *zio)
mutex_exit(&vq->vq_lock);
}
void
vdev_queue_change_io_priority(zio_t *zio, zio_priority_t priority)
{
vdev_queue_t *vq = &zio->io_vd->vdev_queue;
avl_tree_t *tree;
ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
ASSERT3U(priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
if (zio->io_type == ZIO_TYPE_READ) {
if (priority != ZIO_PRIORITY_SYNC_READ &&
priority != ZIO_PRIORITY_ASYNC_READ &&
priority != ZIO_PRIORITY_SCRUB)
priority = ZIO_PRIORITY_ASYNC_READ;
} else {
ASSERT(zio->io_type == ZIO_TYPE_WRITE);
if (priority != ZIO_PRIORITY_SYNC_WRITE &&
priority != ZIO_PRIORITY_ASYNC_WRITE)
priority = ZIO_PRIORITY_ASYNC_WRITE;
}
mutex_enter(&vq->vq_lock);
/*
* If the zio is in none of the queues we can simply change
* the priority. If the zio is waiting to be submitted we must
* remove it from the queue and re-insert it with the new priority.
* Otherwise, the zio is currently active and we cannot change its
* priority.
*/
tree = vdev_queue_class_tree(vq, zio->io_priority);
if (avl_find(tree, zio, NULL) == zio) {
avl_remove(vdev_queue_class_tree(vq, zio->io_priority), zio);
zio->io_priority = priority;
avl_add(vdev_queue_class_tree(vq, zio->io_priority), zio);
} else if (avl_find(&vq->vq_active_tree, zio, NULL) != zio) {
zio->io_priority = priority;
}
mutex_exit(&vq->vq_lock);
}
/*
* As these two methods are only used for load calculations we're not
* concerned if we get an incorrect value on 32bit platforms due to lack of