From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757347AbZETMSR (ORCPT ); Wed, 20 May 2009 08:18:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755004AbZETMSG (ORCPT ); Wed, 20 May 2009 08:18:06 -0400 Received: from casper.infradead.org ([85.118.1.10]:60849 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751776AbZETMSF (ORCPT ); Wed, 20 May 2009 08:18:05 -0400 Subject: Re: [PATCH]cpuset: add new API to change cpuset top group's cpus From: Peter Zijlstra To: Andi Kleen Cc: Len Brown , Shaohua Li , "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "menage@google.com" , Vaidyanathan Srinivasan In-Reply-To: <87ljosnfzb.fsf@basil.nowhere.org> References: <20090519073942.GA10864@sli10-desk.sh.intel.com> <1242722454.26820.461.camel@twins> <20090519084852.GA13682@sli10-desk.sh.intel.com> <1242723364.26820.466.camel@twins> <1242729538.26820.497.camel@twins> <1242772601.26820.527.camel@twins> <87ljosnfzb.fsf@basil.nowhere.org> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 20 May 2009 14:17:05 +0200 Message-Id: <1242821825.26820.583.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2009-05-20 at 13:58 +0200, Andi Kleen wrote: > Could you explain that please? How does changing the top level > cpuset affect other cpu sets? Suppose you have 8 cpus and created 3 cpusets: A: cpu0 - system administration stuff B: cpu1-5 - generic computational stuff C: cpu6-7 - latency critical stuff Each such set is made a load-balance domain (iow load-balancing on the top level set is disabled). Now, suppose someone thinks its a good idea to remove cpu0 because the machine is running against some thermal limit -- what will all the administration stuff (including sshd) do? Same goes for the latency critical stuff. You really want to start shrinking the generic computational capacity first. The thing is, you cannot simply rip cpus out from under a system, people might rely on them being there and have policy attached to them -- esp. people touching cpusets should know that a machine isn't configured homogeneous and any odd cpu will do.