Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Rate limit calls to update_blocked_averages() for NOHZ | From | Dietmar Eggemann <> | Date | Mon, 25 Jan 2021 18:53:45 +0100 |
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On 25/01/2021 18:30, Vincent Guittot wrote: > On Mon, 25 Jan 2021 at 11:45, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: >> >> On 22/01/2021 20:10, Joel Fernandes wrote: >>> Hi Vincent, >>> >>> Thanks for reply. Please see the replies below: >>> >>> On Fri, Jan 22, 2021 at 05:56:22PM +0100, Vincent Guittot wrote: >>>> On Fri, 22 Jan 2021 at 16:46, Joel Fernandes (Google) >>>> <joel@joelfernandes.org> wrote:
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>> If I understood you correctly, you want to avoid these frequent calls >> to update_blocked_averages() here to further avoid invoking sched_util >> via update_blocked_averages() -> cpufreq_update_util() (since 'decayed' >> is set) very often in your setup. > > So It's not clear if the problem that joel wants to raise, is about: > - the running time of update_blocked_averages > - the running time of the cpufreq_update_util which is called because > utilization has decayed during the update of blocked load > - the wake up latency because of newly_idle lb
Pretty much so.
IIRC his interest is driven by the fact that he saw much less activity in newly_idle lb and therefore cpufreq_update_util on a system with the same kernel and userspace but with less CPUs (i.e. also smaller frequency domains) and less cgroups (with blocked load) and started wondering why.
I assume that since he understands this environment now much better, he should be able to come up with better test numbers to show if there is a performance issue on his 2+6 DynamIQ system and if yes, where exactly in this code path.
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