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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
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/zio.c
+38 -5
View File
@@ -539,6 +539,8 @@ zio_walk_children(zio_t *pio, zio_link_t **zl)
{
list_t *cl = &pio->io_child_list;
ASSERT(MUTEX_HELD(&pio->io_lock));
*zl = (*zl == NULL) ? list_head(cl) : list_next(cl, *zl);
if (*zl == NULL)
return (NULL);
@@ -573,8 +575,8 @@ zio_add_child(zio_t *pio, zio_t *cio)
zl->zl_parent = pio;
zl->zl_child = cio;
mutex_enter(&cio->io_lock);
mutex_enter(&pio->io_lock);
mutex_enter(&cio->io_lock);
ASSERT(pio->io_state[ZIO_WAIT_DONE] == 0);
@@ -587,8 +589,8 @@ zio_add_child(zio_t *pio, zio_t *cio)
pio->io_child_count++;
cio->io_parent_count++;
mutex_exit(&pio->io_lock);
mutex_exit(&cio->io_lock);
mutex_exit(&pio->io_lock);
}
static void
@@ -597,8 +599,8 @@ zio_remove_child(zio_t *pio, zio_t *cio, zio_link_t *zl)
ASSERT(zl->zl_parent == pio);
ASSERT(zl->zl_child == cio);
mutex_enter(&cio->io_lock);
mutex_enter(&pio->io_lock);
mutex_enter(&cio->io_lock);
list_remove(&pio->io_child_list, zl);
list_remove(&cio->io_parent_list, zl);
@@ -606,8 +608,8 @@ zio_remove_child(zio_t *pio, zio_t *cio, zio_link_t *zl)
pio->io_child_count--;
cio->io_parent_count--;
mutex_exit(&pio->io_lock);
mutex_exit(&cio->io_lock);
mutex_exit(&pio->io_lock);
kmem_cache_free(zio_link_cache, zl);
}
@@ -1963,14 +1965,16 @@ zio_reexecute(zio_t *pio)
* cannot be affected by any side effects of reexecuting 'cio'.
*/
zio_link_t *zl = NULL;
mutex_enter(&pio->io_lock);
for (cio = zio_walk_children(pio, &zl); cio != NULL; cio = cio_next) {
cio_next = zio_walk_children(pio, &zl);
mutex_enter(&pio->io_lock);
for (int w = 0; w < ZIO_WAIT_TYPES; w++)
pio->io_children[cio->io_child_type][w]++;
mutex_exit(&pio->io_lock);
zio_reexecute(cio);
mutex_enter(&pio->io_lock);
}
mutex_exit(&pio->io_lock);
/*
* Now that all children have been reexecuted, execute the parent.
@@ -3474,6 +3478,35 @@ zio_vdev_io_done(zio_t *zio)
return (ZIO_PIPELINE_CONTINUE);
}
/*
* This function is used to change the priority of an existing zio that is
* currently in-flight. This is used by the arc to upgrade priority in the
* event that a demand read is made for a block that is currently queued
* as a scrub or async read IO. Otherwise, the high priority read request
* would end up having to wait for the lower priority IO.
*/
void
zio_change_priority(zio_t *pio, zio_priority_t priority)
{
zio_t *cio, *cio_next;
zio_link_t *zl = NULL;
ASSERT3U(priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
if (pio->io_vd != NULL && pio->io_vd->vdev_ops->vdev_op_leaf) {
vdev_queue_change_io_priority(pio, priority);
} else {
pio->io_priority = priority;
}
mutex_enter(&pio->io_lock);
for (cio = zio_walk_children(pio, &zl); cio != NULL; cio = cio_next) {
cio_next = zio_walk_children(pio, &zl);
zio_change_priority(cio, priority);
}
mutex_exit(&pio->io_lock);
}
/*
* For non-raidz ZIOs, we can just copy aside the bad data read from the
* disk, and use that to finish the checksum ereport later.