Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Sun, 27 May 2018 11:50:12 +0200 | Subject | Re: [PATCH v3 1/2] sched/cpufreq: always consider blocked FAIR utilization |
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On Thu, May 24, 2018 at 4:10 PM, Patrick Bellasi <patrick.bellasi@arm.com> wrote: > Since the refactoring introduced by: > > commit 8f111bc357aa ("cpufreq/schedutil: Rewrite CPUFREQ_RT support") > > we aggregate FAIR utilization only if this class has runnable tasks. > This was mainly due to avoid the risk to stay on an high frequency just > because of the blocked utilization of a CPU not being properly decayed > while the CPU was idle. > > However, since: > > commit 31e77c93e432 ("sched/fair: Update blocked load when newly idle") > > the FAIR blocked utilization is properly decayed also for IDLE CPUs. > > This allows us to use the FAIR blocked utilization as a safe mechanism > to gracefully reduce the frequency only if no FAIR tasks show up on a > CPU for a reasonable period of time. > > Moreover, we also reduce the frequency drops of CPUs running periodic > tasks which, depending on the task periodicity and the time required > for a frequency switch, was increasing the chances to introduce some > undesirable performance variations. > > Reported-by: Vincent Guittot <vincent.guittot@linaro.org> > Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> > Acked-by: Viresh Kumar <viresh.kumar@linaro.org> > Acked-by: Vincent Guittot <vincent.guittot@linaro.org> > Tested-by: Vincent Guittot <vincent.guittot@linaro.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Vincent Guittot <vincent.guittot@linaro.org> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Cc: Joel Fernandes <joelaf@google.com> > Cc: linux-kernel@vger.kernel.org > Cc: linux-pm@vger.kernel.org
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Or please let me know if you want me to apply this one.
> --- > Changes in v3: > - add "Tested-by" and "Acked-by" Vincent tags > > Changes in v2: > - add "Acked-by" Viresh tag > --- > kernel/sched/cpufreq_schedutil.c | 17 ++++++++--------- > 1 file changed, 8 insertions(+), 9 deletions(-) > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > index e13df951aca7..28592b62b1d5 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -183,22 +183,21 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu) > static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu) > { > struct rq *rq = cpu_rq(sg_cpu->cpu); > - unsigned long util; > > - if (rq->rt.rt_nr_running) { > - util = sg_cpu->max; > - } else { > - util = sg_cpu->util_dl; > - if (rq->cfs.h_nr_running) > - util += sg_cpu->util_cfs; > - } > + if (rq->rt.rt_nr_running) > + return sg_cpu->max; > > /* > + * Utilization required by DEADLINE must always be granted while, for > + * FAIR, we use blocked utilization of IDLE CPUs as a mechanism to > + * gracefully reduce the frequency when no tasks show up for longer > + * periods of time. > + * > * Ideally we would like to set util_dl as min/guaranteed freq and > * util_cfs + util_dl as requested freq. However, cpufreq is not yet > * ready for such an interface. So, we only do the latter for now. > */ > - return min(util, sg_cpu->max); > + return min(sg_cpu->max, (sg_cpu->util_dl + sg_cpu->util_cfs)); > } > > static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time, unsigned int flags) > -- > 2.15.1 >
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