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 967EDC433E1 for ; Fri, 29 May 2020 16:04:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 812BA207BC for ; Fri, 29 May 2020 16:04:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728077AbgE2QEc (ORCPT ); Fri, 29 May 2020 12:04:32 -0400 Received: from foss.arm.com ([217.140.110.172]:38674 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727915AbgE2QEb (ORCPT ); Fri, 29 May 2020 12:04:31 -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 094EF55D; Fri, 29 May 2020 09:04:30 -0700 (PDT) Received: from e107158-lin (e107158-lin.cambridge.arm.com [10.1.195.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 519713F718; Fri, 29 May 2020 09:04:27 -0700 (PDT) Date: Fri, 29 May 2020 17:04:24 +0100 From: Qais Yousef To: Mel Gorman 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: <20200529160423.qsrbzxtcx2jslljk@e107158-lin> 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> <20200529100806.GA3070@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200529100806.GA3070@suse.de> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/29/20 11:08, Mel Gorman wrote: > On Thu, May 28, 2020 at 06:11:12PM +0200, Peter Zijlstra wrote: > > > FWIW, I think you're referring to Mel's notice in OSPM regarding the overhead. > > > Trying to see what goes on in there. > > > > 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. > > During that talk, I was a vague about the cost, admitted I had not looked > too closely at mainline performance and had since deleted the data given > that the problem was first spotted in early April. If I heard someone > else making statements like I did at the talk, I would consider it a bit > vague, potentially FUD, possibly wrong and worth rechecking myself. In > terms of distributions "cannot enable this", we could but I was unwilling > to pay the cost for a feature no one has asked for yet. If they had, I > would endevour to put it behind static branches and disable it by default > (like what happened for PSI). I was contacted offlist about my comments > at OSPM and gathered new data to respond properly. For the record, here > is an editted version of my response; I had this impression too that's why I had a rather humble attempt. [...] > # Event 'cycles:ppp' > # > # Baseline Delta Abs Shared Object Symbol > # ........ ......... ........................ .............................................. > # > 9.59% -2.87% [kernel.vmlinux] [k] poll_idle > 0.19% +1.85% [kernel.vmlinux] [k] activate_task > +1.17% [kernel.vmlinux] [k] dequeue_task > +0.89% [kernel.vmlinux] [k] update_rq_clock.part.73 > 3.88% +0.73% [kernel.vmlinux] [k] try_to_wake_up > 3.17% +0.68% [kernel.vmlinux] [k] __schedule > 1.16% -0.60% [kernel.vmlinux] [k] __update_load_avg_cfs_rq > 2.20% -0.54% [kernel.vmlinux] [k] resched_curr > 2.08% -0.29% [kernel.vmlinux] [k] _raw_spin_lock_irqsave > 0.44% -0.29% [kernel.vmlinux] [k] cpus_share_cache > 1.13% +0.23% [kernel.vmlinux] [k] _raw_spin_lock_bh > > A lot of the uclamp functions appear to be inlined so it is not be > particularly obvious from a raw profile but it shows up in the annotated > profile in activate_task and dequeue_task for example. In the case of > dequeue_task, uclamp_rq_dec_id() is extremely expensive according to the > annotated profile. > > I'm afraid I did not dig into this deeply once I knew I could just disable > it even within the distribution. Could by any chance the vmlinux (with debug symbols hopefully) and perf.dat are still lying around to share? I could send you a link to drop them somewhere. Thanks -- Qais Yousef