From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8FD9C433E0 for ; Fri, 19 Jun 2020 12:17:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC19320776 for ; Fri, 19 Jun 2020 12:17:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732895AbgFSMRe (ORCPT ); Fri, 19 Jun 2020 08:17:34 -0400 Received: from foss.arm.com ([217.140.110.172]:55204 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728712AbgFSMRd (ORCPT ); Fri, 19 Jun 2020 08:17:33 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3F07F101E; Fri, 19 Jun 2020 05:17:32 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 926453F6CF; Fri, 19 Jun 2020 05:17:30 -0700 (PDT) References: <20200618195525.7889-1-qais.yousef@arm.com> <20200618195525.7889-3-qais.yousef@arm.com> <20200619115723.GF3129@suse.de> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Mel Gorman Cc: Qais Yousef , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Patrick Bellasi , Chris Redpath , Lukasz Luba , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] sched/uclamp: Protect uclamp fast path code with static key In-reply-to: <20200619115723.GF3129@suse.de> Date: Fri, 19 Jun 2020 13:17:28 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/06/20 12:57, Mel Gorman wrote: > On Fri, Jun 19, 2020 at 11:36:46AM +0100, Valentin Schneider wrote: >> > nouclamp uclamp uclamp-static-key >> > Hmean send-64 162.43 ( 0.00%) 157.84 * -2.82%* 163.39 * 0.59%* >> > Hmean send-128 324.71 ( 0.00%) 314.78 * -3.06%* 326.18 * 0.45%* >> > Hmean send-256 641.55 ( 0.00%) 628.67 * -2.01%* 648.12 * 1.02%* >> > Hmean send-1024 2525.28 ( 0.00%) 2448.26 * -3.05%* 2543.73 * 0.73%* >> > Hmean send-2048 4836.14 ( 0.00%) 4712.08 * -2.57%* 4867.69 * 0.65%* >> > Hmean send-3312 7540.83 ( 0.00%) 7425.45 * -1.53%* 7621.06 * 1.06%* >> > Hmean send-4096 9124.53 ( 0.00%) 8948.82 * -1.93%* 9276.25 * 1.66%* >> > Hmean send-8192 15589.67 ( 0.00%) 15486.35 * -0.66%* 15819.98 * 1.48%* >> > Hmean send-16384 26386.47 ( 0.00%) 25752.25 * -2.40%* 26773.74 * 1.47%* >> > >> >> Am I reading this correctly in that compiling in uclamp but having the >> static key enabled gives a slight improvement compared to not compiling in >> uclamp? I suppose the important bit is that we're not seeing regressions >> anymore, but still. >> > > I haven't reviewed the series in depth because from your review, another > version is likely in the works. I don't wait Qais to hate me here - I think you could start the performance testing on this version if you feel like it, given my comments were mostly on changelog / debug options - the core of that patch shouldn't change much. > However, it is not that unusual to > see small fluctuations like this that are counter-intuitive. The report > indicates the difference is likely outside of the noise with * around the > percentage difference instead of () but it could be small boot-to-boot > variance, differences in code layout, slight differences in slab usage > patterns etc. The definitive evidence that uclamp overhead is no there > is whether the uclamp functions show up in annotated profiles or not. I see, thanks! I suppose if we have access to individual samples we can also run some statistical tests / stare at some boxplots to see how it compares.