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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
tests/zfs-tests/tests/perf/scripts/prefetch_io.sh
+7 -7
View File
@@ -41,9 +41,9 @@ function get_prefetched_demand_reads
echo $demand_reads
}
function get_sync_wait_for_async
function get_async_upgrade_sync
{
typeset -l sync_wait=`awk '$1 == "sync_wait_for_async" \
typeset -l sync_wait=`awk '$1 == "async_upgrade_sync" \
{ print $3 }' $zfs_kstats/arcstats`
echo $sync_wait
@@ -59,7 +59,7 @@ poolname=$1
interval=$2
prefetch_ios=$(get_prefetch_ios)
prefetched_demand_reads=$(get_prefetched_demand_reads)
sync_wait_for_async=$(get_sync_wait_for_async)
async_upgrade_sync=$(get_async_upgrade_sync)
while true
do
@@ -73,10 +73,10 @@ do
$(( $new_prefetched_demand_reads - $prefetched_demand_reads ))
prefetched_demand_reads=$new_prefetched_demand_reads
new_sync_wait_for_async=$(get_sync_wait_for_async)
printf "%-24s\t%u\n" "sync_wait_for_async" \
$(( $new_sync_wait_for_async - $sync_wait_for_async ))
sync_wait_for_async=$new_sync_wait_for_async
new_async_upgrade_sync=$(get_async_upgrade_sync)
printf "%-24s\t%u\n" "async_upgrade_sync" \
$(( $new_async_upgrade_sync - $async_upgrade_sync ))
async_upgrade_sync=$new_async_upgrade_sync
sleep $interval
done