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SubjectRe: [PATCH 3/5] sched/deadline: Use __sub_running_bw() throughout dl_change_utilization()
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On 7/29/19 5:47 PM, Peter Zijlstra wrote:
> On Fri, Jul 26, 2019 at 09:27:54AM +0100, Dietmar Eggemann wrote:
>> dl_change_utilization() has a BUG_ON() to check that no schedutil
>> kthread (sugov) is entering this function. So instead of calling
>> sub_running_bw() which checks for the special entity related to a
>> sugov thread, call the underlying function __sub_running_bw().
>>
>> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
>> ---
>> kernel/sched/deadline.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index 99d4c24a8637..1fa005f79307 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -164,7 +164,7 @@ void dl_change_utilization(struct task_struct *p, u64 new_bw)
>>
>> rq = task_rq(p);
>> if (p->dl.dl_non_contending) {
>> - sub_running_bw(&p->dl, &rq->dl);
>> + __sub_running_bw(p->dl.dl_bw, &rq->dl);
>> p->dl.dl_non_contending = 0;
>> /*
>> * If the timer handler is currently running and the
>
> I'm confused; the only called of dl_change_utilization() is
> sched_dl_overflow(), and that already checks FLAG_SUGOV and exits before
> calling.

That's right. There is even a BUG_ON(p->dl.flags & SCHED_FLAG_SUGOV) at
the beginning of dl_change_utilization().

> So how can this matter?

We save the 'if (!dl_entity_is_special(dl_se))' from sub_running_bw()
when we call __sub_running_bw() since we know it can't be a special task.

Later in dl_change_utilization() we already use the inner bw accounting
functions __sub_rq_bw() and __add_rq_bw().

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