Messages in this thread | | | Subject | Re: [PATCH] Revert "cpufreq: schedutil: Don't restrict kthread to related_cpus unnecessarily" | From | Dietmar Eggemann <> | Date | Tue, 8 May 2018 11:09:57 +0200 |
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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.
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