Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754166Ab3FRDpF (ORCPT ); Mon, 17 Jun 2013 23:45:05 -0400 Received: from mga02.intel.com ([134.134.136.20]:37037 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753803Ab3FRDpD (ORCPT ); Mon, 17 Jun 2013 23:45:03 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,886,1363158000"; d="scan'208";a="331251478" Message-ID: <51BFD787.5020708@intel.com> Date: Tue, 18 Jun 2013 11:44:07 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Paul Turner CC: Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Andrew Morton , Borislav Petkov , Namhyung Kim , Mike Galbraith , Morten Rasmussen , Vincent Guittot , Preeti U Murthy , Viresh Kumar , LKML , Mel Gorman , Rik van Riel , Michael Wang , Jason Low , Changlong Xie , sgruszka@redhat.com, =?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?= Subject: Re: [patch v8 6/9] sched: compute runnable load avg in cpu_load and cpu_avg_load_per_task References: <1370589652-24549-1-git-send-email-alex.shi@intel.com> <1370589652-24549-7-git-send-email-alex.shi@intel.com> <51BF15C4.1090906@intel.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3742 Lines: 92 On 06/18/2013 07:00 AM, Paul Turner wrote: > On Mon, Jun 17, 2013 at 6:57 AM, Alex Shi wrote: >> > On 06/17/2013 08:17 PM, Paul Turner wrote: >>> >> On Mon, Jun 17, 2013 at 3:51 AM, Paul Turner wrote: >>>> >>> On Fri, Jun 7, 2013 at 12:20 AM, Alex Shi wrote: >>>>> >>>> They are the base values in load balance, update them with rq runnable >>>>> >>>> load average, then the load balance will consider runnable load avg >>>>> >>>> naturally. >>>>> >>>> >>>>> >>>> We also try to include the blocked_load_avg as cpu load in balancing, >>>>> >>>> but that cause kbuild performance drop 6% on every Intel machine, and >>>>> >>>> aim7/oltp drop on some of 4 CPU sockets machines. >>>>> >>>> >>>> >>> >>>> >>> This looks fine. >>>> >>> >>>> >>> Did you try including blocked_load_avg in only get_rq_runnable_load() >>>> >>> [ and not weighted_cpuload() which is called by new-idle ]? >>> >> >>> >> Looking at this more this feels less correct since you're taking >>> >> averages of averages. >>> >> >>> >> This was previously discussed at: >>> >> https://lkml.org/lkml/2013/5/6/109 >>> >> >>> >> And you later replied suggesting this didn't seem to hurt; what's the >>> >> current status there? >> > >> > Yes, your example show the blocked_load_avg value. >> > So I had given a patch for review at that time before do detailed >> > testing. https://lkml.org/lkml/2013/5/7/66 >> > >> > But in detailed testing, the patch cause a big performance regression. >> > When I look into for details. I found some cpu in kbuild just had a big >> > blocked_load_avg, with a very small runnable_load_avg value. >> > >> > Seems accumulating current blocked_load_avg into cpu load isn't a good >> > idea. Because: > So I think this describes an alternate implementation to the one suggested in: > https://lkml.org/lkml/2013/5/7/66 > > Specifically, we _don't_ want to accumulate into cpu-load. Taking an > "average of the average" loses the mobility that the new > representation allows. > >> > 1, The blocked_load_avg is decayed same as runnable load, sometime is >> > far bigger than runnable load, that drive tasks to other idle or slight >> > load cpu, than cause both performance and power issue. But if the >> > blocked load is decayed too fast, it lose its effect. > This is why the idea would be to use an instantaneous load in > weighted_cpuload() and one that incorporated averages on (wants a > rename) get_rq_runnable_load(). > > For non-instaneous load-indexes we're pulling for stability. Paul, could I summary your point here: keep current weighted_cpu_load, but add blocked load avg in get_rq_runnable_load? I will test this change. > >> > 2, Another issue of blocked load is that when waking up task, we can not >> > know blocked load proportion of the task on rq. So, the blocked load is >> > meaningless in wake affine decision. > I think this is confusing two things: > > (a) A wake-idle wake-up > (b) A wake-affine wake-up what's I mean the wake affine is (b). Anyway, blocked load is no help on the scenario. > > In (a) we do not care about the blocked load proportion, only whether > a cpu is idle. > > But once (a) has failed we should absolutely care how much load is > blocked in (b) as: > - We know we're going to queue for bandwidth on the cpu [ otherwise > we'd be in (a) ] > - Blocked load predicts how much _other_ work is expected to also > share the queue with us during the quantum > -- Thanks Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/