Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752078Ab0LVJXs (ORCPT ); Wed, 22 Dec 2010 04:23:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:31569 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751658Ab0LVJXr (ORCPT ); Wed, 22 Dec 2010 04:23:47 -0500 Message-ID: <4D11C362.1060100@redhat.com> Date: Wed, 22 Dec 2010 11:22:42 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.13) Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Lightning/1.0b3pre Thunderbird/3.1.7 MIME-Version: 1.0 To: Frederic Weisbecker CC: Peter Zijlstra , LKML , Thomas Gleixner , "Paul E. McKenney" , Ingo Molnar , Steven Rostedt , Lai Jiangshan , Andrew Morton , Anton Blanchard , Tim Pepper Subject: Re: [RFC PATCH 15/15] nohz_task: Procfs interface References: <1292858662-5650-1-git-send-email-fweisbec@gmail.com> <1292858662-5650-16-git-send-email-fweisbec@gmail.com> <1292859744.5021.4.camel@laptop> <20101220155737.GA1742@nowhere> <1292861799.5021.27.camel@laptop> <20101221012418.GI1715@nowhere> <1292919280.5021.203.camel@laptop> <4D10B2E9.9040806@redhat.com> <20101221170512.GM1750@nowhere> <4D10EF3D.3070000@redhat.com> <20101221210831.GS1750@nowhere> In-Reply-To: <20101221210831.GS1750@nowhere> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1621 Lines: 41 On 12/21/2010 11:08 PM, Frederic Weisbecker wrote: > On Tue, Dec 21, 2010 at 08:17:33PM +0200, Avi Kivity wrote: > > On 12/21/2010 07:05 PM, Frederic Weisbecker wrote: > > >> > > >> For an example of a per-cpu flag that is checked on every exit with > > >> zero additional overhead on the flag clear case, look at > > >> TIF_USER_RETURN_NOTIFY. > > > > > >Right, but the problem is actually that if we want to automate the nohz > > >attribute on every tasks, then you need you have this flag set for > > >all of these threads. > > > > > >No problem with that, but if nobody wants the nohz attribute, we don't > > >need to force that slow path. > > > > When the scheduler detects the task is all alone, it sets the flag; > > when it blocks, or if another task joins, it drops the flag (at most > > one task per cpu has the flag set). > > > > Does that work? > > Makes sense. And that integrates well with Peter's idea of creating a > new cpuset attribute for the nohz tasks. > > But instead of making this detection from the scheduler, I think this > should be done from the tick: if there is only one task running, set > it the TF flag. > > But anyway, that's an optimisation. We can start with setting that flag > on every task in that cpuset. So long as we start without the new knob. -- error compiling committee.c: too many arguments to function -- 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/