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Date: Wed, 13 Jul 2016 14:56:41 +0200 From: Vincent Guittot <vincent.guittot@...aro.org> To: Morten Rasmussen <morten.rasmussen@....com> Cc: Peter Zijlstra <peterz@...radead.org>, "mingo@...hat.com" <mingo@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>, Yuyang Du <yuyang.du@...el.com>, mgalbraith@...e.de, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations balance at wake-up On 22 June 2016 at 19:03, Morten Rasmussen <morten.rasmussen@....com> wrote: > Currently, SD_WAKE_AFFINE always takes priority over wakeup balancing if > SD_BALANCE_WAKE is set on the sched_domains. For asymmetric > configurations SD_WAKE_AFFINE is only desirable if the waking task's > compute demand (utilization) is suitable for all the cpu capacities > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup instead of "suitable for all the cpu capacities available within the SD_WAKE_AFFINE sched_domain", should it be "suitable for local cpu and prev cpu" becasue you only check the capacity of these 2 CPUs. Other than this comment for the commit message, the patch looks good to me Acked-by: Vincent Guittot <vincent.guittot@...aro.org> > balancing take over (find_idlest_{group, cpu}()). > > This patch makes affine wake-ups conditional on whether both the waker > cpu and prev_cpu has sufficient capacity for the waking task, or not. > > It is assumed that the sched_group(s) containing the waker cpu and > prev_cpu only contain cpu with the same capacity (homogeneous). > > Ideally, we shouldn't set 'want_affine' in the first place, but we don't > know if SD_BALANCE_WAKE is enabled on the sched_domain(s) until we start > traversing them. > > cc: Ingo Molnar <mingo@...hat.com> > cc: Peter Zijlstra <peterz@...radead.org> > > Signed-off-by: Morten Rasmussen <morten.rasmussen@....com> > --- > kernel/sched/fair.c | 28 +++++++++++++++++++++++++++- > 1 file changed, 27 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 216db302e87d..dba02c7b57b3 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -114,6 +114,12 @@ unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL; > unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL; > #endif > > +/* > + * The margin used when comparing utilization with cpu capacity: > + * util * 1024 < capacity * margin > + */ > +unsigned int capacity_margin = 1280; /* ~20% */ > + > static inline void update_load_add(struct load_weight *lw, unsigned long inc) > { > lw->weight += inc; > @@ -5260,6 +5266,25 @@ static int cpu_util(int cpu) > return (util >= capacity) ? capacity : util; > } > > +static inline int task_util(struct task_struct *p) > +{ > + return p->se.avg.util_avg; > +} > + > +static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) > +{ > + long min_cap, max_cap; > + > + min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu)); > + max_cap = cpu_rq(cpu)->rd->max_cpu_capacity; > + > + /* Minimum capacity is close to max, no need to abort wake_affine */ > + if (max_cap - min_cap < max_cap >> 3) > + return 0; > + > + return min_cap * 1024 < task_util(p) * capacity_margin; > +} > + > /* > * select_task_rq_fair: Select target runqueue for the waking task in domains > * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE, > @@ -5283,7 +5308,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f > > if (sd_flag & SD_BALANCE_WAKE) { > record_wakee(p); > - want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p)); > + want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) > + && cpumask_test_cpu(cpu, tsk_cpus_allowed(p)); > } > > rcu_read_lock(); > -- > 1.9.1 >
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