From mboxrd@z Thu Jan 1 00:00:00 1970 From: Quentin Perret Subject: Re: [RFC PATCH v2 3/6] sched: Add over-utilization/tipping point indicator Date: Fri, 20 Apr 2018 09:31:18 +0100 Message-ID: <20180420083118.GA14391@e108498-lin.cambridge.arm.com> References: <20180406153607.17815-1-dietmar.eggemann@arm.com> <20180406153607.17815-4-dietmar.eggemann@arm.com> <20180418111729.GB6783@e108498-lin.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Joel Fernandes Cc: Dietmar Eggemann , LKML , Peter Zijlstra , Thara Gopinath , Linux PM , Morten Rasmussen , Chris Redpath , Patrick Bellasi , Valentin Schneider , "Rafael J . Wysocki" , Greg Kroah-Hartman , Vincent Guittot , Viresh Kumar , Todd Kjos , Juri Lelli , Steve Muckle , Eduardo Valentin List-Id: linux-pm@vger.kernel.org On Friday 20 Apr 2018 at 01:14:35 (-0700), Joel Fernandes wrote: > On Fri, Apr 20, 2018 at 1:13 AM, Joel Fernandes wrote: > > On Wed, Apr 18, 2018 at 4:17 AM, Quentin Perret wrote: > >> On Friday 13 Apr 2018 at 16:56:39 (-0700), Joel Fernandes wrote: > >>> Hi, > >>> > >>> On Fri, Apr 6, 2018 at 8:36 AM, Dietmar Eggemann > >>> wrote: > >>> > From: Thara Gopinath > >>> > > >>> > Energy-aware scheduling should only operate when the system is not > >>> > overutilized. There must be cpu time available to place tasks based on > >>> > utilization in an energy-aware fashion, i.e. to pack tasks on > >>> > energy-efficient cpus without harming the overall throughput. > >>> > > >>> > In case the system operates above this tipping point the tasks have to > >>> > be placed based on task and cpu load in the classical way of spreading > >>> > tasks across as many cpus as possible. > >>> > > >>> > The point in which a system switches from being not overutilized to > >>> > being overutilized is called the tipping point. > >>> > > >>> > Such a tipping point indicator on a sched domain as the system > >>> > boundary is introduced here. As soon as one cpu of a sched domain is > >>> > overutilized the whole sched domain is declared overutilized as well. > >>> > A cpu becomes overutilized when its utilization is higher that 80% > >>> > (capacity_margin) of its capacity. > >>> > > >>> > The implementation takes advantage of the shared sched domain which is > >>> > shared across all per-cpu views of a sched domain level. The new > >>> > overutilized flag is placed in this shared sched domain. > >>> > > >>> > Load balancing is skipped in case the energy model is present and the > >>> > sched domain is not overutilized because under this condition the > >>> > predominantly load-per-capacity driven load-balancer should not > >>> > interfere with the energy-aware wakeup placement based on utilization. > >>> > > >>> > In case the total utilization of a sched domain is greater than the > >>> > total sched domain capacity the overutilized flag is set at the parent > >>> > sched domain level to let other sched groups help getting rid of the > >>> > overutilization of cpus. > >>> > > >>> > Signed-off-by: Thara Gopinath > >>> > Signed-off-by: Dietmar Eggemann > >>> > --- > >>> > include/linux/sched/topology.h | 1 + > >>> > kernel/sched/fair.c | 62 ++++++++++++++++++++++++++++++++++++++++-- > >>> > kernel/sched/sched.h | 1 + > >>> > kernel/sched/topology.c | 12 +++----- > >>> > 4 files changed, 65 insertions(+), 11 deletions(-) > >>> > > >>> > diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h > >>> > index 26347741ba50..dd001c232646 100644 > >>> > --- a/include/linux/sched/topology.h > >>> > +++ b/include/linux/sched/topology.h > >>> > @@ -72,6 +72,7 @@ struct sched_domain_shared { > >>> > atomic_t ref; > >>> > atomic_t nr_busy_cpus; > >>> > int has_idle_cores; > >>> > + int overutilized; > >>> > }; > >>> > > >>> > struct sched_domain { > >>> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >>> > index 0a76ad2ef022..6960e5ef3c14 100644 > >>> > --- a/kernel/sched/fair.c > >>> > +++ b/kernel/sched/fair.c > >>> > @@ -5345,6 +5345,28 @@ static inline void hrtick_update(struct rq *rq) > >>> > } > >>> > #endif > >>> > > >>> > +#ifdef CONFIG_SMP > >>> > +static inline int cpu_overutilized(int cpu); > >>> > + > >>> > +static inline int sd_overutilized(struct sched_domain *sd) > >>> > +{ > >>> > + return READ_ONCE(sd->shared->overutilized); > >>> > +} > >>> > + > >>> > +static inline void update_overutilized_status(struct rq *rq) > >>> > +{ > >>> > + struct sched_domain *sd; > >>> > + > >>> > + rcu_read_lock(); > >>> > + sd = rcu_dereference(rq->sd); > >>> > + if (sd && !sd_overutilized(sd) && cpu_overutilized(rq->cpu)) > >>> > + WRITE_ONCE(sd->shared->overutilized, 1); > >>> > + rcu_read_unlock(); > >>> > +} > >>> > +#else > >>> > +static inline void update_overutilized_status(struct rq *rq) {} > >>> > +#endif /* CONFIG_SMP */ > >>> > + > >>> > /* > >>> > * The enqueue_task method is called before nr_running is > >>> > * increased. Here we update the fair scheduling stats and > >>> > @@ -5394,8 +5416,10 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > >>> > update_cfs_group(se); > >>> > } > >>> > > >>> > - if (!se) > >>> > + if (!se) { > >>> > add_nr_running(rq, 1); > >>> > + update_overutilized_status(rq); > >>> > + } > >>> > >>> I'm wondering if it makes sense for considering scenarios whether > >>> other classes cause CPUs in the domain to go above the tipping point. > >>> Then in that case also, it makes sense to not to do EAS in that domain > >>> because of the overutilization. > >>> > >>> I guess task_fits using cpu_util which is PELT only at the moment... > >>> so may require some other method like aggregation of CFS PELT, with > >>> RT-PELT and DL running bw or something. > >>> > >> > >> So at the moment in cpu_overutilized() we comapre cpu_util() to > >> capacity_of() which should include RT and IRQ pressure IIRC. But > >> you're right, we might be able to do more here... Perhaps we > >> could also use cpu_util_dl() which is available in sched.h now ? > > > > Yes, should be Ok, and then when RT utilization stuff is available, > > then that can be included in the equation as well (probably for now > > you could use rt_avg). > > > > Another crazy idea is to check the contribution of higher classes in > > one-shot with (capacity_orig_of - capacity_of) although I think that > > method would be less instantaneous/accurate. > > Just to add to the last point, the capacity_of also factors in the IRQ > contribution if I remember correctly, which is probably a good thing? > I think so too yes. But actually, since we compare cpu_util() to capacity_of() in cpu_overutilized(), the current implementation should already be fairly similar to the "capacity_orig_of - capacity_of" implementation you're suggesting I guess. And I agree that when Vincent's RT PELT patches get merged we should probably use that :-) Thanks ! Quentin