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SubjectRe: [PATCH v3 1/3] sched: Fix UCLAMP_FLAG_IDLE setting
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?


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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