From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754619AbaBLXFC (ORCPT ); Wed, 12 Feb 2014 18:05:02 -0500 Received: from mail-we0-f182.google.com ([74.125.82.182]:36541 "EHLO mail-we0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754202AbaBLXFB (ORCPT ); Wed, 12 Feb 2014 18:05:01 -0500 Date: Thu, 13 Feb 2014 00:04:57 +0100 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Tejun Heo , Kevin Hilman , Lai Jiangshan , Zoran Markovic , linux-kernel@vger.kernel.org, Shaibal Dutta , Dipankar Sarma Subject: Re: [RFC PATCH] rcu: move SRCU grace period work to power efficient workqueue Message-ID: <20140212230454.GA14383@localhost.localdomain> References: <1391197986-12774-1-git-send-email-zoran.markovic@linaro.org> <52F8A51F.4090909@cn.fujitsu.com> <20140210184729.GL4250@linux.vnet.ibm.com> <20140212182336.GD5496@localhost.localdomain> <20140212190241.GD4250@linux.vnet.ibm.com> <20140212192354.GC26809@htj.dyndns.org> <20140212195922.GE4250@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140212195922.GE4250@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > Cc: Frederic Weisbecker > Cc: Tejun Heo > > 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 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