LKML Archive on lore.kernel.org help / color / mirror / Atom feed
From: Quentin Perret <email@example.com> To: Dietmar Eggemann <firstname.lastname@example.org> Cc: Viresh Kumar <email@example.com>, firstname.lastname@example.org, Peter Zijlstra <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, email@example.com, Pavan Kondeti <firstname.lastname@example.org>, "Rafael J . Wysocki" <email@example.com>, Juri Lelli <firstname.lastname@example.org>, Joel Fernandes <email@example.com>, Patrick Bellasi <firstname.lastname@example.org> Subject: Re: [PATCH] Revert "cpufreq: schedutil: Don't restrict kthread to related_cpus unnecessarily" Date: Tue, 8 May 2018 10:42:37 +0100 [thread overview] Message-ID: <20180508094237.GA3752@e108498-lin.cambridge.arm.com> (raw) In-Reply-To: <email@example.com> On Tuesday 08 May 2018 at 11:09:57 (+0200), Dietmar Eggemann wrote: > On 05/08/2018 10:22 AM, Viresh Kumar wrote: > > On 08-05-18, 08:33, Dietmar Eggemann wrote: > > > This reverts commit e2cabe48c20efb174ce0c01190f8b9c5f3ea1d13. > > > > > > Lifting the restriction that the sugov kthread is bound to the > > > policy->related_cpus for a system with a slow switching cpufreq driver, > > > which is able to perform DVFS from any cpu (e.g. cpufreq-dt), is not > > > only not beneficial it also harms Enery-Aware Scheduling (EAS) on > > > systems with asymmetric cpu capacities (e.g. Arm big.LITTLE). > > > > > > The sugov kthread which does the update for the little cpus could > > > potentially run on a big cpu. It could prevent that the big cluster goes > > > into deeper idle states although all the tasks are running on the little > > > cluster. > > > > I think the original patch did the right thing, but that doesn't suit > > everybody as you explained. > > > > I wouldn't really revert the patch but fix my platform's cpufreq > > driver to set dvfs_possible_from_any_cpu = false, so that other > > platforms can still benefit from the original commit. > > This would make sure that the kthreads are bound to the correct set of cpus > for platforms with those cpufreq drivers (cpufreq-dt (h960), scmi-cpufreq, > scpi-cpufreq) but it will also change the logic (e.g. > sugov_should_update_freq() -> cpufreq_can_do_remote_dvfs()). > > I'm still struggling to understand when a driver/platform should set > dvfs_possible_from_any_cpu to true and what the actual benefit would be. I assume it might be beneficial to have the kthread moving around freely in some cases, but since it is a SCHED_DEADLINE task now it can't really migrate anywhere anyway. So I'm not sure either if this commits still makes sense now. Or is there another use case for this ? Thanks, Quentin
next prev parent reply other threads:[~2018-05-08 9:42 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-08 7:33 [PATCH] Revert "cpufreq: schedutil: Don't restrict kthread to related_cpus unnecessarily" Dietmar Eggemann 2018-05-08 8:22 ` Viresh Kumar 2018-05-08 9:09 ` Dietmar Eggemann 2018-05-08 9:42 ` Quentin Perret [this message] 2018-05-13 5:19 ` Joel Fernandes 2018-05-17 19:10 ` Saravana Kannan 2018-05-17 19:13 ` Joel Fernandes 2018-05-08 9:45 ` Viresh Kumar 2018-05-08 10:02 ` Quentin Perret 2018-05-08 10:34 ` Viresh Kumar 2018-05-08 11:00 ` Quentin Perret 2018-05-08 11:14 ` Viresh Kumar 2018-05-08 11:24 ` Quentin Perret 2018-05-08 12:20 ` Juri Lelli 2018-05-08 20:36 ` Rafael J. Wysocki 2018-05-09 4:55 ` Viresh Kumar 2018-05-08 10:36 ` Dietmar Eggemann 2018-05-08 10:53 ` Viresh Kumar 2018-05-08 12:17 ` Juri Lelli 2018-05-09 4:55 ` Viresh Kumar 2018-05-17 10:32 ` Rafael J. Wysocki
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20180508094237.GA3752@e108498-lin.cambridge.arm.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).