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Disable high priority ZIO threads on FreeBSD and Linux

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High priority threads are handling ZIL writes.  While there is no
ZIL compression, there is encryption, checksuming and RAIDZ math.
We've found that on large systems 1 taskq with 5 threads can be
a bottleneck for throughput, IOPS or both. Instead of just bumping
number of threads with a risk of overloading CPUs and increasing
latency, switch to using TQ_FRONT mechanism to increase sync write
requests priority within standard write threads.  Do not do it on
Illumos, since its TQ_FRONT implementation is inherently unfair.
FreeBSD and Linux don't have this problem, so we can do it there.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #16146
This commit is contained in:
Alexander Motin
2024-05-03 12:53:34 -04:00
committed by GitHub
parent 8f1b7a6fa6
commit 04bae5ec95
3 changed files with 16 additions and 9 deletions
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module/zfs/zio.c
+7 -5
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@@ -2041,12 +2041,14 @@ zio_taskq_dispatch(zio_t *zio, zio_taskq_type_t q, boolean_t cutinline)
/*
* If this is a high priority I/O, then use the high priority taskq if
* available.
* available or cut the line otherwise.
*/
if ((zio->io_priority == ZIO_PRIORITY_NOW ||
zio->io_priority == ZIO_PRIORITY_SYNC_WRITE) &&
spa->spa_zio_taskq[t][q + 1].stqs_count != 0)
q++;
if (zio->io_priority == ZIO_PRIORITY_SYNC_WRITE) {
if (spa->spa_zio_taskq[t][q + 1].stqs_count != 0)
q++;
else
flags |= TQ_FRONT;
}
ASSERT3U(q, <, ZIO_TASKQ_TYPES);