Commit bbf393b0 authored by Paul E. McKenney's avatar Paul E. McKenney

Documentation/kernel-per-CPU-kthreads.txt: Workqueue affinity

This commit documents the ability to apply CPU affinity to WQ_SYSFS
workqueues, thus offloading them from the desired worker CPUs.
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 586dd56a
......@@ -162,7 +162,18 @@ Purpose: Execute workqueue requests
To reduce its OS jitter, do any of the following:
1. Run your workload at a real-time priority, which will allow
preempting the kworker daemons.
2. Do any of the following needed to avoid jitter that your
2. A given workqueue can be made visible in the sysfs filesystem
by passing the WQ_SYSFS to that workqueue's alloc_workqueue().
Such a workqueue can be confined to a given subset of the
CPUs using the /sys/devices/virtual/workqueue/*/cpumask sysfs
files. The set of WQ_SYSFS workqueues can be displayed using
"ls sys/devices/virtual/workqueue". That said, the workqueues
maintainer would like to caution people against indiscriminately
sprinkling WQ_SYSFS across all the workqueues. The reason for
caution is that it is easy to add WQ_SYSFS, but because sysfs is
part of the formal user/kernel API, it can be nearly impossible
to remove it, even if its addition was a mistake.
3. Do any of the following needed to avoid jitter that your
application cannot tolerate:
a. Build your kernel with CONFIG_SLUB=y rather than
CONFIG_SLAB=y, thus avoiding the slab allocator's periodic
......
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