From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id C4A1C7D072 for ; Wed, 23 May 2018 17:35:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933870AbeEWRe7 (ORCPT ); Wed, 23 May 2018 13:34:59 -0400 Received: from foss.arm.com ([217.140.101.70]:59200 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932667AbeEWRe6 (ORCPT ); Wed, 23 May 2018 13:34:58 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 873751435; Wed, 23 May 2018 10:34:58 -0700 (PDT) Received: from e110439-lin (e110439-lin.cambridge.arm.com [10.1.210.68]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DCC103F589; Wed, 23 May 2018 10:34:55 -0700 (PDT) Date: Wed, 23 May 2018 18:34:53 +0100 From: Patrick Bellasi To: Waiman Long Cc: Tejun Heo , Li Zefan , Johannes Weiner , Peter Zijlstra , Ingo Molnar , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@fb.com, pjt@google.com, luto@amacapital.net, Mike Galbraith , torvalds@linux-foundation.org, Roman Gushchin , Juri Lelli Subject: Re: [PATCH v8 4/6] cpuset: Make generate_sched_domains() recognize isolated_cpus Message-ID: <20180523173453.GY30654@e110439-lin> References: <1526590545-3350-1-git-send-email-longman@redhat.com> <1526590545-3350-5-git-send-email-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1526590545-3350-5-git-send-email-longman@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Waiman, On 17-May 16:55, Waiman Long wrote: [...] > @@ -672,13 +672,14 @@ static int generate_sched_domains(cpumask_var_t **domains, > int ndoms = 0; /* number of sched domains in result */ > int nslot; /* next empty doms[] struct cpumask slot */ > struct cgroup_subsys_state *pos_css; > + bool root_load_balance = is_sched_load_balance(&top_cpuset); > > doms = NULL; > dattr = NULL; > csa = NULL; > > /* Special case for the 99% of systems with one, full, sched domain */ > - if (is_sched_load_balance(&top_cpuset)) { > + if (root_load_balance && !top_cpuset.isolation_count) { Perhaps I'm missing something but, it seems to me that, when the two conditions above are true, then we are going to destroy and rebuild the exact same scheduling domains. IOW, on 99% of systems where: is_sched_load_balance(&top_cpuset) top_cpuset.isolation_count = 0 since boot time and forever, then every time we update a value for cpuset.cpus we keep rebuilding the same SDs. It's not strictly related to this patch, the same already happens in mainline based just on the first condition, but since you are extending that optimization, perhaps you can tell me where I'm possibly wrong or which cases I'm not considering. I'm interested mainly because on Android systems those conditions are always true and we see SDs rebuilds every time we write something in cpuset.cpus, which ultimately accounts for almost all the 6-7[ms] time required for the write to return, depending on the CPU frequency. Cheers Patrick -- #include Patrick Bellasi -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html