Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753942AbaBLUN3 (ORCPT ); Wed, 12 Feb 2014 15:13:29 -0500 Received: from e37.co.us.ibm.com ([32.97.110.158]:59472 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753731AbaBLUNZ (ORCPT ); Wed, 12 Feb 2014 15:13:25 -0500 Date: Wed, 12 Feb 2014 11:59:22 -0800 From: "Paul E. McKenney" To: Tejun Heo Cc: Frederic Weisbecker , 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: <20140212195922.GE4250@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140212192354.GC26809@htj.dyndns.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14021220-7164-0000-0000-000005F09A5D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 application cannot tolerate: a. Build your kernel with CONFIG_SLUB=y rather than CONFIG_SLAB=y, thus avoiding the slab allocator's periodic -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/