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