From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757389Ab2EILCe (ORCPT ); Wed, 9 May 2012 07:02:34 -0400 Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:57291 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752533Ab2EILCc convert rfc822-to-8bit (ORCPT ); Wed, 9 May 2012 07:02:32 -0400 MIME-Version: 1.0 In-Reply-To: <1336537289.7365.62.camel@marge.simpson.net> References: <1335830115-14335-1-git-send-email-fweisbec@gmail.com> <1335830115-14335-8-git-send-email-fweisbec@gmail.com> <1336488626.16236.41.camel@twins> <1336490832.8226.5.camel@twins> <1336492081.8226.13.camel@twins> <1336493768.8226.29.camel@twins> <1336506601.7400.21.camel@marge.simpson.net> <1336537289.7365.62.camel@marge.simpson.net> Date: Wed, 9 May 2012 13:02:30 +0200 Message-ID: Subject: Re: [PATCH 07/41] cpuset: Set up interface for nohz flag From: Frederic Weisbecker To: Mike Galbraith Cc: Christoph Lameter , Peter Zijlstra , LKML , linaro-sched-sig@lists.linaro.org, Alessio Igor Bogani , Andrew Morton , Avi Kivity , Chris Metcalf , Daniel Lezcano , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Ingo Molnar , Kevin Hilman , Max Krasnyansky , "Paul E. McKenney" , Stephen Hemminger , Steven Rostedt , Sven-Thorsten Dietrich , Thomas Gleixner Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2012/5/9 Mike Galbraith : > On Tue, 2012-05-08 at 15:45 -0500, Christoph Lameter wrote: >> On Tue, 8 May 2012, Mike Galbraith wrote: >> >> > On Tue, 2012-05-08 at 18:16 +0200, Peter Zijlstra wrote: >> > > On Tue, 2012-05-08 at 10:57 -0500, Christoph Lameter wrote: >> > >> > > isolcpus is a very limited hack that adds more pain that its worth. Its >> > > yet another mask to check and its functionality is completely available >> > > through cpusets. >> > >> > Agreed. >> >> How would that work? By creating cpusets that only have a single cpu in >> them? > > No, just turn load balancing off for exclusive set, domains go poof. I don't think it's >> > > You cannot cree multi-cpu partitions using isolcpus, you cannot >> > > dynamically reconfigure it. >> > >> > Big plus for cpusets. >> >> Why would you want to do anything like it? cpusets are confusing. You can >> have a cpu be part of multiple cpusets. Which nohz setting applies for a >> particular cpu then? If any of the cpusets have nohz set then it applies >> to the cpu? And thus someone in a cpuset that does not has nohz set will >> find that a cpu will have nohz functionality? > > nohz has to be at least an exclusive set property. > >> Its not a good match for this. You would want a per cpu attribute for >> nohz. > > Or per cpuset, which can be the same thing as per cpu if you want. > >> > > And on the scheduler side cpusets doesn't add runtime overhead to normal >> > > things, only sched_setaffinity() and a few other rare operations get >> > > slightly more expensive. And it allows to reduce runtime overhead by >> > > making the load-balancer domains smaller. >> > >> > Very big deal if you have a load that doesn't do all the performance 'i' >> > dotting and 't' crossing it maybe could have, but ends up on a big box. >> >> isolcpus are not part of load balancer domains. > > Yup, so if you have an application with an RT component, somewhat > sensitive, needs isolation from rest of a big box, but app also has > SCHED_OTHER components.  isolcpus is a pain, everything has to be static > and nailed to the floor.  Load just works when plugged into a cpuset. > > -Mike >