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Date: Wed, 25 May 2016 14:57:00 +0800 From: Wanpeng Li <kernellwp@...il.com> To: Morten Rasmussen <morten.rasmussen@....com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>, yuyang.du@...el.com, Vincent Guittot <vincent.guittot@...aro.org>, Mike Galbraith <mgalbraith@...e.de>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 09/16] sched/fair: Let asymmetric cpu configurations balance at wake-up 2016-05-23 18:58 GMT+08:00 Morten Rasmussen <morten.rasmussen@....com>: > 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. > > 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; > +} If one task util_avg is SCHED_CAPACITY_SCALE and running on x86 box w/ SMT enabled, then each HT has capacity 589, wake_cap() will result in always not wake affine, right? Regards, Wanpeng Li > + > /* > * 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(); > -- > 1.9.1 > -- Regards, Wanpeng Li
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