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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 5E28CC433DF for ; Thu, 25 Jun 2020 15:44:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3681220706 for ; Thu, 25 Jun 2020 15:44:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405814AbgFYPoB (ORCPT ); Thu, 25 Jun 2020 11:44:01 -0400 Received: from foss.arm.com ([217.140.110.172]:58260 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405159AbgFYPoA (ORCPT ); Thu, 25 Jun 2020 11:44:00 -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 19478D6E; Thu, 25 Jun 2020 08:44:00 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 526D13F6CF; Thu, 25 Jun 2020 08:43:58 -0700 (PDT) From: Qais Yousef To: Ingo Molnar , Peter Zijlstra Cc: Valentin Schneider , Qais Yousef , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Patrick Bellasi , Chris Redpath , Lukasz Luba , linux-kernel@vger.kernel.org Subject: [PATCH v4 0/2] sched: Optionally skip uclamp logic in fast path Date: Thu, 25 Jun 2020 16:43:50 +0100 Message-Id: <20200625154352.24767-1-qais.yousef@arm.com> X-Mailer: git-send-email 2.17.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This series attempts to address the report that uclamp logic could be expensive sometimes and shows a regression in netperf UDP_STREAM under certain conditions. The first patch is a fix for how struct uclamp_rq is initialized which is required by the 2nd patch which contains the real 'fix'. Worth noting that the root cause of the overhead is believed to be system specific or related to potential certain code/data layout issues, leading to worse I/D $ performance. Different systems exhibited different behaviors and the regression did disappear in certain kernel version while attempting to reporoduce. More info can be found here: https://lore.kernel.org/lkml/20200616110824.dgkkbyapn3io6wik@e107158-lin/ Having the static key seemed the best thing to do to ensure the effect of uclamp is minimized for kernels that compile it in but don't have a userspace that uses it, which will allow distros to distribute uclamp capable kernels by default without having to compromise on performance for some systems that could be affected. Changes in v4: * Fix broken boosting of RT tasks when static key is disabled. Changes in v3: * Avoid double negatives and rename the static key to uclamp_used * Unconditionally enable the static key through any of the paths where the user can modify the default uclamp value. * Use C99 named struct initializer for struct uclamp_rq which is easier to read than the memset(). Changes in v2: * Add more info in the commit message about the result of perf diff to demonstrate that the activate/deactivate_task pressure is reduced in the fast path. * Fix sparse warning reported by the test robot. * Add an extra commit about using static_branch_likely() instead of static_branc_unlikely(). Thanks -- Qais Yousef Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman CC: Patrick Bellasi Cc: Chris Redpath Cc: Lukasz Luba Cc: linux-kernel@vger.kernel.org Qais Yousef (2): sched/uclamp: Fix initialization of struct uclamp_rq sched/uclamp: Protect uclamp fast path code with static key kernel/sched/core.c | 80 ++++++++++++++++++++++++++++---- kernel/sched/cpufreq_schedutil.c | 2 +- kernel/sched/sched.h | 7 +++ 3 files changed, 79 insertions(+), 10 deletions(-) -- 2.17.1