sched/cpufreq_schedutil: use util_est for OPP selection

- backport util-est from linux-power.git

When schedutil looks at the CPU utilization, the current PELT value for
that CPU is returned straight away. In certain scenarios this can have
undesired side effects and delays on frequency selection.

For example, since the task utilization is decayed at wakeup time, a
long sleeping big task newly enqueued does not add immediately a
significant contribution to the target CPU. This introduces some latency
before schedutil will be able to detect the best frequency required by
that task.

Moreover, the PELT signal build-up time is a function of the current
frequency, because of the scale invariant load tracking support. Thus,
starting from a lower frequency, the utilization build-up time will
increase even more and further delays the selection of the actual
frequency which better serves the task requirements.

In order to reduce this kind of latencies, we integrate the usage
of the CPU's estimated utilization in the sugov_get_util function.
This allows to properly consider the expected utilization of a CPU which,
for example, has just got a big task running after a long sleep period.
Ultimately this allows to select the best frequency to run a task
right after its wake-up.

Change-Id: Ibf98a4be222546733cbd88b9a8f2c8858319dd96
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Paul Turner <pjt@google.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index dd9c84dd60563273b76e9b32dde7973883754d25..f5606acd5312f93eaad6fc151e37dbc2148ff923 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1890,14 +1890,20 @@ static inline unsigned long cpu_util(int cpu)
 
 static inline unsigned long cpu_util_freq(int cpu)
 {
-       unsigned long util = cpu_rq(cpu)->cfs.avg.util_avg;
+       struct cfs_rq *cfs_rq = &cpu_rq(cpu)->cfs;
        unsigned long capacity = capacity_orig_of(cpu);
+       unsigned long util = READ_ONCE(cfs_rq->avg.util_avg);
 
 #ifdef CONFIG_SCHED_WALT
        if (!walt_disabled && sysctl_sched_use_walt_cpu_util) {
                walt_util(util, cpu_rq(cpu)->prev_runnable_sum);
        }
 #endif
+       if (sched_feat(UTIL_EST)) {
+               util = max_t(unsigned long, util,
+                            READ_ONCE(rq->cfs.avg.util_est.enqueued));
+       }
+
        return (util >= capacity) ? capacity : util;
 }