Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH] Revert "cpufreq: schedutil: Don't restrict kthread to related_cpus unnecessarily" | Date | Thu, 17 May 2018 12:32:29 +0200 |
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On Wednesday, May 9, 2018 6:55:27 AM CEST 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. > > > > Example: hikey960 w/ 4.16.0-rc6-+ > > Arm big.LITTLE with per-cluster DVFS > > > > root@h960:~# cat /proc/cpuinfo | grep "^CPU part" > > CPU part : 0xd03 (Cortex-A53, little cpu) > > CPU part : 0xd03 > > CPU part : 0xd03 > > CPU part : 0xd03 > > CPU part : 0xd09 (Cortex-A73, big cpu) > > CPU part : 0xd09 > > CPU part : 0xd09 > > CPU part : 0xd09 > > > > root@h960:/sys/devices/system/cpu/cpufreq# ls > > policy0 policy4 schedutil > > > > root@h960:/sys/devices/system/cpu/cpufreq# cat policy*/related_cpus > > 0 1 2 3 > > 4 5 6 7 > > > > (1) w/o the revert: > > > > root@h960:~# ps -eo pid,class,rtprio,pri,psr,comm | awk 'NR == 1 || > > /sugov/' > > PID CLS RTPRIO PRI PSR COMMAND > > 1489 #6 0 140 1 sugov:0 > > 1490 #6 0 140 0 sugov:4 > > > > The sugov kthread sugov:4 responsible for policy4 runs on cpu0. (In this > > case both sugov kthreads run on little cpus). > > > > cross policy (cluster) remote callback example: > > ... > > migration/1-14 [001] enqueue_task_fair: this_cpu=1 cpu_of(rq)=5 > > migration/1-14 [001] sugov_update_shared: this_cpu=1 sg_cpu->cpu=5 > > sg_cpu->sg_policy->policy->related_cpus=4-7 > > sugov:4-1490 [000] sugov_work: this_cpu=0 > > sg_cpu->sg_policy->policy->related_cpus=4-7 > > ... > > > > The remote callback (this_cpu=1, target_cpu=5) is executed on cpu=0. > > > > (2) w/ the revert: > > > > root@h960:~# ps -eo pid,class,rtprio,pri,psr,comm | awk 'NR == 1 || > > /sugov/' > > PID CLS RTPRIO PRI PSR COMMAND > > 1491 #6 0 140 2 sugov:0 > > 1492 #6 0 140 4 sugov:4 > > > > The sugov kthread sugov:4 responsible for policy4 runs on cpu4. > > > > cross policy (cluster) remote callback example: > > ... > > migration/1-14 [001] enqueue_task_fair: this_cpu=1 cpu_of(rq)=7 > > migration/1-14 [001] sugov_update_shared: this_cpu=1 sg_cpu->cpu=7 > > sg_cpu->sg_policy->policy->related_cpus=4-7 > > sugov:4-1492 [004] sugov_work: this_cpu=4 > > sg_cpu->sg_policy->policy->related_cpus=4-7 > > ... > > > > The remote callback (this_cpu=1, target_cpu=7) is executed on cpu=4. > > > > Now the sugov kthread executes again on the policy (cluster) for which > > the Operating Performance Point (OPP) should be changed. > > It avoids the problem that an otherwise idle policy (cluster) is running > > schedutil (the sugov kthread) for another one. > > > > Cc: Viresh Kumar <viresh.kumar@linaro.org> > > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: Pavan Kondeti <pkondeti@codeaurora.org> > > Cc: Juri Lelli <juri.lelli@redhat.com> > > Cc: Joel Fernandes <joelaf@google.com> > > Cc: Patrick Bellasi <patrick.bellasi@arm.com> > > Cc: Quentin Perret <quentin.perret@arm.com> > > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > > --- > > kernel/sched/cpufreq_schedutil.c | 6 +----- > > 1 file changed, 1 insertion(+), 5 deletions(-) > > > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > > index d2c6083304b4..63014cff76a5 100644 > > --- a/kernel/sched/cpufreq_schedutil.c > > +++ b/kernel/sched/cpufreq_schedutil.c > > @@ -523,11 +523,7 @@ static int sugov_kthread_create(struct sugov_policy *sg_policy) > > } > > > > sg_policy->thread = thread; > > - > > - /* Kthread is bound to all CPUs by default */ > > - if (!policy->dvfs_possible_from_any_cpu) > > - kthread_bind_mask(thread, policy->related_cpus); > > - > > + kthread_bind_mask(thread, policy->related_cpus); > > init_irq_work(&sg_policy->irq_work, sugov_irq_work); > > mutex_init(&sg_policy->work_lock); > > > > Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Applied, thanks!
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