Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751731AbaAOKic (ORCPT ); Wed, 15 Jan 2014 05:38:32 -0500 Received: from merlin.infradead.org ([205.233.59.134]:33259 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751673AbaAOKi3 (ORCPT ); Wed, 15 Jan 2014 05:38:29 -0500 Date: Wed, 15 Jan 2014 11:38:08 +0100 From: Peter Zijlstra To: Viresh Kumar Cc: =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Kevin Hilman , Vincent Guittot , Amit Kucheria , Lists linaro-kernel , Linaro Networking , Linux Kernel Mailing List , Steven Rostedt Subject: Re: [QUERY]: Is using CPU hotplug right for isolating CPUs? Message-ID: <20140115103808.GY31570@twins.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 15, 2014 at 02:57:36PM +0530, Viresh Kumar wrote: > Hi Again, > > I am now successful in isolating a CPU completely using CPUsets, > NO_HZ_FULL and CPU hotplug.. > > My setup and requirements for those who weren't following the > earlier mails: > > For networking machines it is required to run data plane threads on > some CPUs (i.e. one thread per CPU) and these CPUs shouldn't be > interrupted by kernel at all. > > Earlier I tried CPUSets with NO_HZ by creating two groups with > load_balancing disabled between them and manually tried to move > all tasks out to CPU0 group. But even then there were interruptions > which were continuously coming on CPU1 (which I am trying to > isolate). These were some workqueue events, some timers (like > prandom), timer overflow events (As NO_HZ_FULL pushes hrtimer > to long ahead in future, 450 seconds, rather than disabling them > completely, and these hardware timers were overflowing their > counters after 90 seconds on Samsung Exynos board). > > So after creating CPUsets I hotunplugged CPU1 and added it back > immediately. This moved all these interruptions away and now > CPU1 is running my single thread ("stress") for ever. > > Now my question is: Is there anything particularly wrong about using > hotplugging here ? Will that lead to a disaster :) Nah, its just ugly and we should fix it. You need to be careful to not place tasks in a cpuset you're going to unplug though, that'll give funny results. -- 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/