From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751190Ab2EIEVk (ORCPT ); Wed, 9 May 2012 00:21:40 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:57346 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750758Ab2EIEVj (ORCPT ); Wed, 9 May 2012 00:21:39 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX18RvRZWpOcR3Vu4XpHNR6/6nhpCVQOEb4RENOKyAI g65azQd2t7jY2g Message-ID: <1336537289.7365.62.camel@marge.simpson.net> Subject: Re: [PATCH 07/41] cpuset: Set up interface for nohz flag From: Mike Galbraith To: Christoph Lameter 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 Date: Wed, 09 May 2012 06:21:29 +0200 In-Reply-To: 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> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > > 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