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Message-ID: <1464073437.3743.37.camel@suse.de> Date: Tue, 24 May 2016 09:03:57 +0200 From: Mike Galbraith <mgalbraith@...e.de> To: Morten Rasmussen <morten.rasmussen@....com>, peterz@...radead.org, mingo@...hat.com Cc: dietmar.eggemann@....com, yuyang.du@...el.com, vincent.guittot@...aro.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 09/16] sched/fair: Let asymmetric cpu configurations balance at wake-up On Mon, 2016-05-23 at 11:58 +0100, Morten Rasmussen 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 the cpu capacities > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup > balancing take over (find_idlest_{group, cpu}()). > > The assumption is that SD_WAKE_AFFINE is never set for a sched_domain > containing cpus with different capacities. This is enforced by a > previous patch based on the SD_ASYM_CPUCAPACITY flag. > > 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. This doesn't look like it's restricted to big/little setups, so could overrule wake_wide() wanting to NAK a x-node pull. > > > > 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 564215d..ce44fa7 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; > > @@ -5293,6 +5299,25 @@ 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 delta; > > +> > > > long prev_cap = capacity_of(prev_cpu); > > + > > +> > > > delta = cpu_rq(cpu)->rd->max_cpu_capacity - prev_cap; > > + > > +> > > > /* prev_cpu is fairly close to max, no need to abort wake_affine */ > > +> > > > if (delta < prev_cap >> 3) > > +> > > > > > return 0; > > + > > +> > > > return prev_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, > > @@ -5316,7 +5341,8 @@ 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();
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