4.17-stable review patch. If anyone has any objections, please let me know.
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From: Patrick Bellasi patrick.bellasi@arm.com
[ Upstream commit 8ecf04e11283a28ca88b8b8049ac93c3a99fcd2c ]
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 Tested-by: Vincent Guittot vincent.guittot@linaro.org Signed-off-by: Patrick Bellasi patrick.bellasi@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Thomas Gleixner tglx@linutronix.de Acked-by: Viresh Kumar viresh.kumar@linaro.org Acked-by: Vincent 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.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/cpufreq_schedutil.c | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-)
--- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -183,22 +183,21 @@ static void sugov_get_util(struct sugov_ 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)