Since the refactoring introduced by:

   commit 8f111bc3 ("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 31e77c93 ("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: NVincent Guittot <vincent.guittot@linaro.org>
Tested-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPatrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NVincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Steve Muckle <smuckle@google.com>
Link: http://lkml.kernel.org/r/20180524141023.13765-2-patrick.bellasi@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>