| Message ID | 20180206144131.31233-4-patrick.bellasi@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | Utilization estimation (util_est) for FAIR tasks | expand |
On Tue, Feb 6, 2018 at 3:41 PM, Patrick Bellasi <patrick.bellasi@arm.com> wrote: > 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. > > Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > 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 Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > --- > Changes in v4: > - rebased on today's tip/sched/core (commit 460e8c3340a2) > - use util_est.enqueued for cfs_rq's util_est (Joel) > - simplify cpu_util_cfs() integration (Dietmar) > > Changes in v3: > - rebase on today's tip/sched/core (commit 07881166a892) > - moved into Juri's cpu_util_cfs(), which should also > address Rafael's suggestion to use a local variable. > > Changes in v2: > - rebase on top of v4.15-rc2 > - tested that overhauled PELT code does not affect the util_est > > Change-Id: I62c01ed90d8ad45b06383be03d39fcf8c9041646 > --- > kernel/sched/sched.h | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 2e95505e23c6..f3c7b6a83ef4 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -2127,7 +2127,12 @@ static inline unsigned long cpu_util_dl(struct rq *rq) > > static inline unsigned long cpu_util_cfs(struct rq *rq) > { > - return rq->cfs.avg.util_avg; > + if (!sched_feat(UTIL_EST)) > + return rq->cfs.avg.util_avg; > + > + return max_t(unsigned long, > + rq->cfs.avg.util_avg, > + rq->cfs.avg.util_est.enqueued); > } > > #endif > -- > 2.15.1 >
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 2e95505e23c6..f3c7b6a83ef4 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2127,7 +2127,12 @@ static inline unsigned long cpu_util_dl(struct rq *rq) static inline unsigned long cpu_util_cfs(struct rq *rq) { - return rq->cfs.avg.util_avg; + if (!sched_feat(UTIL_EST)) + return rq->cfs.avg.util_avg; + + return max_t(unsigned long, + rq->cfs.avg.util_avg, + rq->cfs.avg.util_est.enqueued); } #endif