From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755242Ab2EHUps (ORCPT ); Tue, 8 May 2012 16:45:48 -0400 Received: from smtp108.prem.mail.ac4.yahoo.com ([76.13.13.47]:42703 "HELO smtp108.prem.mail.ac4.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753681Ab2EHUpr (ORCPT ); Tue, 8 May 2012 16:45:47 -0400 X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: IlP0QK4VM1mTsj5r.bJFgNBO5jIDNw58NPYToSQaRAnHnpc VCfVS5KT90Rjt_ujid_m1QfWVcEelIMq1fkkyvxnp0pH2cmjYTbbPGpnV3Ce EnVGfbFsanWOltXq9Tto0dRJ975f1sAxjRjrltEi5bMhNh3NCxeN9qkzwSh6 LaJ3A4SRI96wY1MvX80j3bAgc4GjHZ.i_.h3Wb0kG_bORbETntDpSeCe57PN MA8QeYl5lOQ9nsVVfF.q8591vxFGdrKZQAku.7lMvS431ddgSvPfZqygJrO3 41iJZHb2VtNdqi95YU0fKRHZO3iP6CcbO_MqkDo8qh7TJ_vfk6Qdh34jsFT4 ZnyiciAGPG378Avl5bW7_VeLH08EXlvkLSZhLn55q4TdtK6uRSnSS_IFYBe4 W X-Yahoo-SMTP: _Dag8S.swBC1p4FJKLCXbs8NQzyse1SYSgnAbY0- Date: Tue, 8 May 2012 15:45:38 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@router.home To: Mike Galbraith cc: Peter Zijlstra , Frederic Weisbecker , 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 Subject: Re: [PATCH 07/41] cpuset: Set up interface for nohz flag In-Reply-To: <1336506601.7400.21.camel@marge.simpson.net> Message-ID: 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> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > > 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? Its not a good match for this. You would want a per cpu attribute for nohz. > > 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.