Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752690AbcJJS3e (ORCPT ); Mon, 10 Oct 2016 14:29:34 -0400 Received: from mail-lf0-f41.google.com ([209.85.215.41]:35071 "EHLO mail-lf0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752476AbcJJS3d (ORCPT ); Mon, 10 Oct 2016 14:29:33 -0400 MIME-Version: 1.0 In-Reply-To: References: <20160923115808.2330-1-matt@codeblueprint.co.uk> <20160928101422.GR5016@twins.programming.kicks-ass.net> <20160928193731.GD16071@codeblueprint.co.uk> <20161010100107.GZ16071@codeblueprint.co.uk> From: Vincent Guittot Date: Mon, 10 Oct 2016 20:29:01 +0200 Message-ID: Subject: Re: [PATCH] sched/fair: Do not decay new task load on first enqueue To: Dietmar Eggemann Cc: Matt Fleming , Wanpeng Li , Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org" , Mike Galbraith , Yuyang Du Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3681 Lines: 87 On 10 October 2016 at 15:54, Dietmar Eggemann wrote: > On 10/10/16 13:29, Vincent Guittot wrote: >> On 10 October 2016 at 12:01, Matt Fleming wrote: >>> On Sun, 09 Oct, at 11:39:27AM, Wanpeng Li wrote: >>>> >>>> The difference between this patch and Peterz's is your patch have a >>>> delta since activate_task()->enqueue_task() does do update_rq_clock(), >>>> so why don't have the delta will cause low cpu machines (4 or 8) to >>>> regress against your another reply in this thread? >>> >>> Both my patch and Peter's patch cause issues with low cpu machines. In >>> <20161004201105.GP16071@codeblueprint.co.uk> I said, >>> >>> "This patch causes some low cpu machines (4 or 8) to regress. It turns >>> out they regress with my patch too." >>> >>> Have I misunderstood your question? >>> >>> I ran out of time to investigate this last week, though I did try all >>> proposed patches, including Vincent's, and none of them produced wins >>> across the board. >> >> I have tried to reprocude your issue on my target an hikey board (ARM >> based octo cores) but i failed to see a regression with commit >> 7dc603c9028e. Neverthless, i can see tasks not been well spread > > Wasn't this about the two patches mentioned in this thread? The one from > Matt using 'se->sum_exec_runtime' in the if condition in > enqueue_entity_load_avg() and Peterz's conditional call to > update_rq_clock(rq) in enqueue_task()? I was trying to reproduce the regression that Matt mentioned at the beg of the thread not those linked to proposed fixes > >> during fork as you mentioned. So I have studied a bit more the >> spreading issue during fork last week and i have a new version of my >> proposed patch that i'm going to send soon. With this patch, i can see >> a good spread of tasks during the fork sequence and some kind of perf >> improvement even if it's bit difficult as the variance is quite >> important with hackbench test so it's mainly an improvement of >> repeatability of the result > > Hikey (ARM64 2x4 cpus) board: cpufreq: performance, cpuidle: disabled > > Performance counter stats for 'perf bench sched messaging -g 20 -l 500' > (10 runs): > > (1) tip/sched/core: commit 447976ef4fd0 > > 5.902209533 seconds time elapsed ( +- 0.31% ) This seems to be too long to test the impact of the forking phase of hackbench > > (2) tip/sched/core + original patch on the 'sched/fair: Do not decay > new task load on first enqueue' thread (23/09/16) > > 5.919933030 seconds time elapsed ( +- 0.44% ) > > (3) tip/sched/core + Peter's ENQUEUE_NEW patch on the 'sched/fair: Do > not decay new task load on first enqueue' thread (28/09/16) > > 5.970195534 seconds time elapsed ( +- 0.37% ) > > Not sure if we can call this a regression but it also shows no > performance gain. > >>> >>> I should get a bit further this week. >>> >>> Vincent, Dietmar, did you guys ever get around to submitting your PELT >>> tracepoint patches? Getting some introspection into the scheduler's >> >> My tarcepoint are not in a shape to be submitted and would need a >> cleanup as some are more hacks for debugging than real trace events. >> Nevertheless, i can push them on a git branch if they can be useful >> for someone > > We carry two trace events locally, one for PELT on se and one for > cfs_rq's (I have to add the runnable bits here) which work for > CONFIG_FAIR_GROUP_SCHED and !CONFIG_FAIR_GROUP_SCHED. I put them into > __update_load_avg(), attach_entity_load_avg() and > detach_entity_load_avg(). I could post them but so far mainline has been > reluctant to see the need for PELT related trace events ... > > [...]