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 <mi...@redhat.com>
> > cc: Peter Zijlstra <pet...@infradead.org>
> >
> > Signed-off-by: Morten Rasmussen <morten.rasmus...@arm.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();
