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_2 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 4A0CDC433DF for ; Mon, 8 Jun 2020 14:44:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 305002076C for ; Mon, 8 Jun 2020 14:44:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730073AbgFHOo2 (ORCPT ); Mon, 8 Jun 2020 10:44:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:51574 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729989AbgFHOo2 (ORCPT ); Mon, 8 Jun 2020 10:44:28 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 88E75206C3; Mon, 8 Jun 2020 14:44:25 +0000 (UTC) Date: Mon, 8 Jun 2020 10:44:24 -0400 From: Steven Rostedt To: Qais Yousef Cc: Vincent Guittot , Mel Gorman , Patrick Bellasi , Dietmar Eggemann , Peter Zijlstra , Ingo Molnar , Randy Dunlap , Jonathan Corbet , Juri Lelli , Ben Segall , Luis Chamberlain , Kees Cook , Iurii Zaikin , Quentin Perret , Valentin Schneider , Pavan Kondeti , linux-doc@vger.kernel.org, linux-kernel , linux-fs Subject: Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Message-ID: <20200608104424.10781990@gandalf.local.home> In-Reply-To: <20200608123102.6sdhdhit7lac5cfl@e107158-lin.cambridge.arm.com> References: <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> <87v9k84knx.derkling@matbug.net> <20200603101022.GG3070@suse.de> <20200603165200.v2ypeagziht7kxdw@e107158-lin.cambridge.arm.com> <20200608123102.6sdhdhit7lac5cfl@e107158-lin.cambridge.arm.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 8 Jun 2020 13:31:03 +0100 Qais Yousef wrote: > I admit I don't know how much of these numbers is ftrace overhead. When trying Note, if you want to get a better idea of how long a function runs, put it into set_ftrace_filter, and then trace it. That way you remove the overhead of the function graph tracer when its nesting within a function. > to capture similar runs for uclamp, the numbers didn't add up compared to > running the test without ftrace generating the graph. If juno is suffering from > bad branching costs in this path, then I suspect ftrace will amplify this as > AFAIU it'll cause extra jumps on entry and exit. > > > > sched-pipe-6532 [001] 9407.276302: funcgraph_entry: | deactivate_task() { > sched-pipe-6532 [001] 9407.276302: funcgraph_entry: | dequeue_task_fair() { > sched-pipe-6532 [001] 9407.276303: funcgraph_entry: | update_curr() { > sched-pipe-6532 [001] 9407.276304: funcgraph_entry: 0.780 us | update_min_vruntime(); > sched-pipe-6532 [001] 9407.276306: funcgraph_entry: | cpuacct_charge() { > sched-pipe-6532 [001] 9407.276306: funcgraph_entry: 0.820 us | __rcu_read_lock(); > sched-pipe-6532 [001] 9407.276308: funcgraph_entry: 0.740 us | __rcu_read_unlock(); The above is more accurate than... > sched-pipe-6532 [001] 9407.276309: funcgraph_exit: 3.980 us | } this one. Because this one has nested tracing within it. -- Steve > sched-pipe-6532 [001] 9407.276310: funcgraph_entry: 0.720 us | __rcu_read_lock(); > sched-pipe-6532 [001] 9407.276312: funcgraph_entry: 0.720 us | __rcu_read_unlock(); > sched-pipe-6532 [001] 9407.276313: funcgraph_exit: 9.840 us | } > sched-pipe-6532 [001] 9407.276314: funcgraph_entry: | __update_load_avg_se() { > sched-pipe-6532 [001] 9407.276315: funcgraph_entry: 0.720 us | __accumulate_pelt_segments(); > sched-pipe-6532 [001] 9407.276316: funcgraph_exit: 2.260 us | } > sched-pipe-6532 [001] 9407.276317: funcgraph_entry: | __update_load_avg_cfs_rq() { > sched-pipe-6532 [001] 9407.276318: funcgraph_entry: 0.860 us | __accumulate_pelt_segments(); > sched-pipe-6532 [001] 9407.276319: funcgraph_exit: 2.340 us | }