On Wed, Aug 02 2017 at 13:24, Peter Zijlstra wrote:
> On Wed, Aug 02, 2017 at 02:10:02PM +0100, Brendan Jackman wrote:
>> We use task_util in find_idlest_group via capacity_spare_wake. This
>> task_util is updated in wake_cap. However wake_cap is not the only
>> reason for ending up in find_idlest_group - we could have been sent
>> there by wake_wide. So explicitly sync the task util with prev_cpu
>> when we are about to head to find_idlest_group.
>>
>> We could simply do this at the beginning of
>> select_task_rq_fair (i.e. irrespective of whether we're heading to
>> select_idle_sibling or find_idlest_group & co), but I didn't want to
>> slow down the select_idle_sibling path more than necessary.
>>
>> Don't do this during fork balancing, we won't need the task_util and
>> we'd just clobber the last_update_time, which is supposed to be 0.
>
> So I remember Morten explicitly not aging util of tasks on wakeup
> because the old util was higher and better representative of what the
> new util would be, or something along those lines.
>
> Morten?
>
>> Signed-off-by: Brendan Jackman <[email protected]>
>> Cc: Dietmar Eggemann <[email protected]>
>> Cc: Vincent Guittot <[email protected]>
>> Cc: Josef Bacik <[email protected]>
>> Cc: Ingo Molnar <[email protected]>
>> Cc: Morten Rasmussen <[email protected]>
>> Cc: Peter Zijlstra <[email protected]>
>> ---
>> kernel/sched/fair.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index c95880e216f6..62869ff252b4 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5913,6 +5913,14 @@ select_task_rq_fair(struct task_struct *p, int
>> prev_cpu, int sd_flag, int wake_f
>> new_cpu = cpu;
>> }
>>
>> + if (sd && !(sd_flag & SD_BALANCE_FORK))
>> + /*
>> + * We're going to need the task's util for capacity_spare_wake
>> + * in select_idlest_group. Sync it up to prev_cpu's
>> + * last_update_time.
>> + */
>> + sync_entity_load_avg(&p->se);
>> +
>
> That has missing {}
OK. Also just noticed it refers to "select_idlest_group", will change to
"find_idlest_group".
>
>
>> if (!sd) {
>> pick_cpu:
>
> And if this patch lives, can you please fix up that broken label indent?
Sure.
>> if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
Cheers,
Brendan
