On 02/13/2014 08:33 AM, Paul E. McKenney wrote: > On Thu, Feb 13, 2014 at 12:04:57AM +0100, Frederic Weisbecker wrote: >> 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: > > 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 > >
Reviewed-by: Lai Jiangshan <la...@cn.fujitsu.com> -- 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/
