From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754494Ab3AKOud (ORCPT ); Fri, 11 Jan 2013 09:50:33 -0500 Received: from mga14.intel.com ([143.182.124.37]:32599 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753841Ab3AKOuc (ORCPT ); Fri, 11 Jan 2013 09:50:32 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,452,1355126400"; d="scan'208";a="190186837" Message-ID: <50F026B4.20906@intel.com> Date: Fri, 11 Jan 2013 22:50:28 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120912 Thunderbird/15.0.1 MIME-Version: 1.0 To: Morten Rasmussen 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 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> <20130111100757.GH2046@e103034-lin> In-Reply-To: <20130111100757.GH2046@e103034-lin> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/11/2013 06:07 PM, Morten Rasmussen wrote: > 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. I didn't know any machine has this flag, but if just some cpu overlap, not stay alone without any domain, the patch won't miss eligible cpu. > > Morten > >> >> >> -- >> Thanks Alex >> > -- Thanks Alex