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SubjectRe: [PATCH v3 1/3] sched: Fix UCLAMP_FLAG_IDLE setting
On 07/01/21 12:43, Quentin Perret wrote:
> On Thursday 01 Jul 2021 at 12:08:03 (+0100), Qais Yousef wrote:
> > On 07/01/21 10:07, Quentin Perret wrote:
> > > On Wednesday 30 Jun 2021 at 15:45:14 (+0000), Quentin Perret wrote:
> > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > > index b094da4c5fea..c0b999a8062a 100644
> > > > --- a/kernel/sched/core.c
> > > > +++ b/kernel/sched/core.c
> > > > @@ -980,7 +980,6 @@ static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
> > > > if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
> > > > return;
> > > >
> > > > - rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
> > > > WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
> > > > }
> > > >
> > > > @@ -1253,6 +1252,10 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
> > > >
> > > > for_each_clamp_id(clamp_id)
> > > > uclamp_rq_inc_id(rq, p, clamp_id);
> > > > +
> > > > + /* Reset clamp idle holding when there is one RUNNABLE task */
> > > > + if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
> > > > + rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
> > > > }
> > > >
> > > > static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
> > > > @@ -1300,6 +1303,13 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
> > > > if (p->uclamp[clamp_id].active) {
> > > > uclamp_rq_dec_id(rq, p, clamp_id);
> > > > uclamp_rq_inc_id(rq, p, clamp_id);
> > > > +
> > > > + /*
> > > > + * Make sure to clear the idle flag if we've transiently reached
> > > > + * 0 uclamp active tasks on the rq.
> > > > + */
> > > > + if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
> > > > + rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
> > >
> > > Bah, now that I had coffee I realize this has the exact same problem.
> > > Let me look at this again ...
> >
> > Hehe uclamp has this effect. It's all obvious, until it's not :-)
>
> Indeed ... :)
>
> > Yes this needs to be out of the loop.
>
> Right or maybe we can just check that uclamp_id == UCLAMP_MAX here and
> we should be good to go? That is, what about the below?

Wouldn't it be better to do this from uclamp_idle_reset() then?

Thanks

--
Qais Yousef

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b094da4c5fea..8e9b8106a0df 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -980,7 +980,6 @@ static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
> if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
> return;
>
> - rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
> WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
> }
>
> @@ -1253,6 +1252,10 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
>
> for_each_clamp_id(clamp_id)
> uclamp_rq_inc_id(rq, p, clamp_id);
> +
> + /* Reset clamp idle holding when there is one RUNNABLE task */
> + if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
> + rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
> }
>
> static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
> @@ -1300,6 +1303,13 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
> if (p->uclamp[clamp_id].active) {
> uclamp_rq_dec_id(rq, p, clamp_id);
> uclamp_rq_inc_id(rq, p, clamp_id);
> +
> + /*
> + * Make sure to clear the idle flag if we've transiently reached
> + * 0 active tasks on rq.
> + */
> + if (clamp_id == MAX && rq->uclamp_flags & UCLAMP_FLAG_IDLE)
> + rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
> }
>
> task_rq_unlock(rq, p, &rf);

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