On Wed, Feb 12, 2014 at 04:33:11PM -0800, Paul E. McKenney wrote: > > Fair point! I wordsmithed it into the following. Seem reasonable? > > 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> > Reviewed-by: Tejun Heo <t...@kernel.org> > Acked-by: Frederic Weisbecker <fweis...@gmail.com> > > 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 >
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