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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E3CA0C433E0 for ; Fri, 29 May 2020 10:22:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB44E2074B for ; Fri, 29 May 2020 10:22:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725681AbgE2KWB (ORCPT ); Fri, 29 May 2020 06:22:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:47014 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725936AbgE2KVf (ORCPT ); Fri, 29 May 2020 06:21:35 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 569FFB117; Fri, 29 May 2020 10:21:31 +0000 (UTC) Date: Fri, 29 May 2020 11:21:25 +0100 From: Mel Gorman To: Qais Yousef Cc: Peter Zijlstra , Ingo Molnar , Randy Dunlap , Jonathan Corbet , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Luis Chamberlain , Kees Cook , Iurii Zaikin , Quentin Perret , Valentin Schneider , Patrick Bellasi , Pavan Kondeti , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Message-ID: <20200529102125.GB3070@suse.de> References: <20200511154053.7822-1-qais.yousef@arm.com> <20200528132327.GB706460@hirez.programming.kicks-ass.net> <20200528155800.yjrmx3hj72xreryh@e107158-lin.cambridge.arm.com> <20200528161112.GI2483@worktop.programming.kicks-ass.net> <20200528165130.m5unoewcncuvxynn@e107158-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20200528165130.m5unoewcncuvxynn@e107158-lin.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, May 28, 2020 at 05:51:31PM +0100, Qais Yousef wrote: > > Indeed, that one. The fact that regular distros cannot enable this > > feature due to performance overhead is unfortunate. It means there is a > > lot less potential for this stuff. > > I had a humble try to catch the overhead but wasn't successful. The observation > wasn't missed by us too then. > As with all things, it's perfectly possible I was looking at a workload where the cost is more obvious but given that the functions are inlined, it's not trivial to spot. I just happened to spot it because I was paying close attention to try_to_wake_up() at the time. > On my Ubuntu 18.04 machine uclamp is enabled by default by the way. 5.3 kernel > though, so uclamp task group stuff not there yet. Should check how their server > distro looks like. > Elsewhere in the thread, I showed some results based on 5.7 so uclamp task group existed but I had it disabled. The uclamp related parts of the kconfig were # zgrep UCLAMP kconfig-5.7.0-rc7-with-clamp.txt.gz CONFIG_UCLAMP_TASK=y CONFIG_UCLAMP_BUCKETS_COUNT=5 # CONFIG_UCLAMP_TASK_GROUP is not set -- Mel Gorman SUSE Labs