From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v8 4/6] cpuset: Make generate_sched_domains() recognize isolated_cpus Date: Wed, 23 May 2018 16:18:53 -0400 Message-ID: References: <1526590545-3350-1-git-send-email-longman@redhat.com> <1526590545-3350-5-git-send-email-longman@redhat.com> <20180523173453.GY30654@e110439-lin> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180523173453.GY30654@e110439-lin> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Patrick Bellasi 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 On 05/23/2018 01:34 PM, Patrick Bellasi wrote: > 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 > Yes, that is true. I will look into how to further optimize this. Thanks for the suggestion. -Longman