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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
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/spa.c
+8 -3
View File
@@ -170,14 +170,19 @@ static const char *const zio_taskq_types[ZIO_TASKQ_TYPES] = {
* that scales with the number of CPUs.
*
* The different taskq priorities are to handle the different contexts (issue
* and interrupt) and then to reserve threads for ZIO_PRIORITY_NOW I/Os that
* need to be handled with minimum delay.
* and interrupt) and then to reserve threads for high priority I/Os that
* need to be handled with minimum delay. Illumos taskq has unfair TQ_FRONT
* implementation, so separate high priority threads are used there.
*/
static zio_taskq_info_t zio_taskqs[ZIO_TYPES][ZIO_TASKQ_TYPES] = {
/* ISSUE ISSUE_HIGH INTR INTR_HIGH */
{ ZTI_ONE, ZTI_NULL, ZTI_ONE, ZTI_NULL }, /* NULL */
{ ZTI_N(8), ZTI_NULL, ZTI_SCALE, ZTI_NULL }, /* READ */
#ifdef illumos
{ ZTI_SYNC, ZTI_N(5), ZTI_SCALE, ZTI_N(5) }, /* WRITE */
#else
{ ZTI_SYNC, ZTI_NULL, ZTI_SCALE, ZTI_NULL }, /* WRITE */
#endif
{ ZTI_SCALE, ZTI_NULL, ZTI_ONE, ZTI_NULL }, /* FREE */
{ ZTI_ONE, ZTI_NULL, ZTI_ONE, ZTI_NULL }, /* CLAIM */
{ ZTI_ONE, ZTI_NULL, ZTI_ONE, ZTI_NULL }, /* FLUSH */
@@ -1217,7 +1222,7 @@ spa_taskqs_fini(spa_t *spa, zio_type_t t, zio_taskq_type_t q)
*
* Example (the defaults for READ and WRITE)
* zio_taskq_read='fixed,1,8 null scale null'
* zio_taskq_write='sync fixed,1,5 scale fixed,1,5'
* zio_taskq_write='sync null scale null'
*
* Each sets the entire row at a time.
*
module/zfs/zio.c
+7 -5
View File
@@ -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);