On Wed, Feb 12, 2014 at 11:59:22AM -0800, Paul E. McKenney wrote: > 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
Acked-by: Frederic Weisbecker <fweis...@gmail.com> I just suggest we append a small explanation about what WQ_SYSFS is about. Like: +2. + The workqueues that want to be visible on the sysfs hierarchy + set the WQ_SYSFS flag. + For those who have this flag set, you can use the + /sys/devices/virtual/workqueue/*/cpumask sysfs files + to force the 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
