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SubjectRe: [PATCH v3 1/6] cpufreq: schedutil: reset sg_cpus's flags at IDLE enter
On 30-Nov 14:12, Juri Lelli wrote:
> Hi,
>
> On 30/11/17 11:47, Patrick Bellasi wrote:
>
> [...]
>
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 2f52ec0f1539..67339ccb5595 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -347,6 +347,12 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> >
> > sg_cpu->util = util;
> > sg_cpu->max = max;
> > +
> > + /* CPU is entering IDLE, reset flags without triggering an update */
> > + if (unlikely(flags & SCHED_CPUFREQ_IDLE)) {
> > + sg_cpu->flags = 0;
> > + goto done;
> > + }
>
> Looks good for now. I'm just thinking that we will happen for DL, as a
> CPU that still "has" a sleeping task is not going to be really idle
> until the 0-lag time.

AFAIU, for the time being, DL already cannot really rely on this flag
for its behaviors to be correct. Indeed, flags are reset as soon as
a FAIR task wakes up and it's enqueued.

Only once your DL integration patches are in, we do not depends on
flags anymore since DL will report a ceratain utilization up to the
0-lag time, isn't it?

If that's the case, I would say that the flags will be used only to
jump to the max OPP for RT tasks. Thus, this patch should still be valid.

> I guess we could move this at that point in time?

Not sure what you mean here. Right now the new SCHED_CPUFREQ_IDLE flag
is notified only by idle tasks. That's the only code path where we are
sure the CPU is entering IDLE.

> > sg_cpu->flags = flags;
> >
> > sugov_set_iowait_boost(sg_cpu, time, flags);
> > @@ -361,6 +367,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> > sugov_update_commit(sg_policy, time, next_f);
> > }
> >
> > +done:
> > raw_spin_unlock(&sg_policy->update_lock);
> > }
> >
> > diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
> > index d518664cce4f..6e8ae2aa7a13 100644
> > --- a/kernel/sched/idle_task.c
> > +++ b/kernel/sched/idle_task.c
> > @@ -30,6 +30,10 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
> > put_prev_task(rq, prev);
> > update_idle_core(rq);
> > schedstat_inc(rq->sched_goidle);
> > +
> > + /* kick cpufreq (see the comment in kernel/sched/sched.h). */
> > + cpufreq_update_util(rq, SCHED_CPUFREQ_IDLE);
>
> Don't know if it make things any cleaner, but you could add to the
> comment that we don't actually trigger a frequency update with this
> call.

Right, will add on next posting.

> Best,
>
> Juri

Cheers Patrick

--
#include <best/regards.h>

Patrick Bellasi

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