On Wed, Feb 12, 2014 at 07:23:38PM +0100, Frederic Weisbecker wrote:
> On Mon, Feb 10, 2014 at 10:47:29AM -0800, Paul E. McKenney wrote:
> > On Mon, Feb 10, 2014 at 06:08:31PM +0800, Lai Jiangshan wrote:
> > > Acked-by: Lai Jiangshan <la...@cn.fujitsu.com>
> >
> > Thank you all, queued for 3.15.
> >
> > We should also have some facility for moving the SRCU workqueues to
> > housekeeping/timekeeping kthreads in the NO_HZ_FULL case. Or does
> > this patch already have that effect?
>
> Kevin Hilman and me plan to try to bring a new Kconfig option that could let
> us control the unbound workqueues affinity through sysfs.
Please CC me or feel free to update Documentation/kernel-per-CPU-kthreads.txt
as part of this upcoming series.
> The feature actually exist currently but is only enabled for workqueues that
> have WQ_SYSFS. Writeback and raid5 are the only current users.
>
> See for example: /sys/devices/virtual/workqueue/writeback/cpumask
Ah, news to me! I have queued the following patch, seem reasonable?
Thanx, Paul
------------------------------------------------------------------------
diff --git a/Documentation/kernel-per-CPU-kthreads.txt
b/Documentation/kernel-per-CPU-kthreads.txt
index 827104fb9364..09f28841ee3e 100644
--- a/Documentation/kernel-per-CPU-kthreads.txt
+++ b/Documentation/kernel-per-CPU-kthreads.txt
@@ -162,7 +162,11 @@ 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".
+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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