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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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man/man4/zfs.4
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@@ -2367,7 +2367,7 @@ This is an advanced debugging parameter.
Don't change this unless you understand what it does.
Set values only apply to pools imported/created after that.
.
.It Sy zio_taskq_write Ns = Ns Sy sync fixed,1,5 scale fixed,1,5 Pq charp
.It Sy zio_taskq_write Ns = Ns Sy sync null scale null Pq charp
Set the queue and thread configuration for the IO write queues.
This is an advanced debugging parameter.
Don't change this unless you understand what it does.