On Thu, May 24, 2018 at 4:10 PM, Patrick Bellasi
<patrick.bell...@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.guit...@linaro.org>
> Signed-off-by: Patrick Bellasi <patrick.bell...@arm.com>
> Acked-by: Viresh Kumar <viresh.ku...@linaro.org>
> Acked-by: Vincent Guittot <vincent.guit...@linaro.org>
> Tested-by: Vincent Guittot <vincent.guit...@linaro.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> Cc: Vincent Guittot <vincent.guit...@linaro.org>
> Cc: Viresh Kumar <viresh.ku...@linaro.org>
> Cc: Joel Fernandes <joe...@google.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux...@vger.kernel.org
Reviewed-by: Rafael J. Wysocki <rafael.j.wyso...@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
>
