From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754814Ab3AKKIA (ORCPT ); Fri, 11 Jan 2013 05:08:00 -0500 Received: from service87.mimecast.com ([91.220.42.44]:33468 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754559Ab3AKKH7 convert rfc822-to-8bit (ORCPT ); Fri, 11 Jan 2013 05:07:59 -0500 Date: Fri, 11 Jan 2013 10:07:57 +0000 From: Morten Rasmussen To: Alex Shi Cc: "mingo@redhat.com" , "peterz@infradead.org" , "tglx@linutronix.de" , "akpm@linux-foundation.org" , "arjan@linux.intel.com" , "bp@alien8.de" , "pjt@google.com" , "namhyung@kernel.org" , "efault@gmx.de" , "vincent.guittot@linaro.org" , "gregkh@linuxfoundation.org" , "preeti@linux.vnet.ibm.com" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v3 05/22] sched: remove domain iterations in fork/exec/wake Message-ID: <20130111100757.GH2046@e103034-lin> References: <1357375071-11793-1-git-send-email-alex.shi@intel.com> <1357375071-11793-6-git-send-email-alex.shi@intel.com> <20130109182102.GC2046@e103034-lin> <50EF7D07.6080006@intel.com> MIME-Version: 1.0 In-Reply-To: <50EF7D07.6080006@intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-OriginalArrivalTime: 11 Jan 2013 10:07:53.0159 (UTC) FILETIME=[84FFE570:01CDEFE3] X-MC-Unique: 113011110075415201 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 11, 2013 at 02:46:31AM +0000, Alex Shi wrote: > On 01/10/2013 02:21 AM, Morten Rasmussen wrote: > >> new_cpu = find_idlest_cpu(group, p, cpu); > >> > - > >> > - /* Now try balancing at a lower domain level of new_cpu */ > >> > - cpu = new_cpu; > >> > - weight = sd->span_weight; > >> > - sd = NULL; > >> > - for_each_domain(cpu, tmp) { > >> > - if (weight <= tmp->span_weight) > >> > - break; > >> > - if (tmp->flags & sd_flag) > >> > - sd = tmp; > >> > - } > >> > - /* while loop will break here if sd == NULL */ > > I agree that this should be a major optimization. I just can't figure > > out why the existing recursive search for an idle cpu switches to the > > new cpu near the end and then starts a search for an idle cpu in the new > > cpu's domain. Is this to handle some exotic sched domain configurations? > > If so, they probably wouldn't work with your optimizations. > > I did not find odd configuration that asking for old logical. > > According to Documentation/scheduler/sched-domains.txt, Maybe never. > "A domain's span MUST be a superset of it child's span (this restriction > could be relaxed if the need arises), and a base domain for CPU i MUST > span at least i." etc. etc. The reason for my suspicion is the SD_OVERLAP flag, which has something to do overlapping sched domains. I haven't looked into what it does or how it works. I'm just wondering if this optimization will affect the use of that flag. Morten > > > -- > Thanks Alex >