On Wed, Feb 12, 2014 at 02:23:54PM -0500, Tejun Heo wrote:
> Hello,
>
> On Wed, Feb 12, 2014 at 11:02:41AM -0800, Paul E. McKenney wrote:
> > +2. Use the /sys/devices/virtual/workqueue/*/cpumask sysfs files
> > + to force the WQ_SYSFS workqueues to run on the specified set
> > + of CPUs. The set of WQ_SYSFS workqueues can be displayed using
> > + "ls sys/devices/virtual/workqueue".
>
> One thing to be careful about is that once published, it becomes part
> of userland visible interface. Maybe adding some words warning
> against sprinkling WQ_SYSFS willy-nilly is a good idea?
Good point! How about the following?
Thanx, Paul
------------------------------------------------------------------------
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 <paul...@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Tejun Heo <t...@kernel.org>
diff --git a/Documentation/kernel-per-CPU-kthreads.txt
b/Documentation/kernel-per-CPU-kthreads.txt
index 827104fb9364..214da3a47a68 100644
--- a/Documentation/kernel-per-CPU-kthreads.txt
+++ b/Documentation/kernel-per-CPU-kthreads.txt
@@ -162,7 +162,16 @@ 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. Use the /sys/devices/virtual/workqueue/*/cpumask sysfs files
+ to force the WQ_SYSFS workqueues to run on the specified set
+ of CPUs. 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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