From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
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 <paul...@linux.vnet.ibm.com>
Reviewed-by: Tejun Heo <t...@kernel.org>
Acked-by: Frederic Weisbecker <fweis...@gmail.com>
Reviewed-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
Documentation/kernel-per-CPU-kthreads.txt | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/Documentation/kernel-per-CPU-kthreads.txt
b/Documentation/kernel-per-CPU-kthreads.txt
index 827104fb9364..f3cd299fcc41 100644
--- a/Documentation/kernel-per-CPU-kthreads.txt
+++ b/Documentation/kernel-per-CPU-kthreads.txt
@@ -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
--
1.8.1.5
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