Messages in this thread | | | Date | Thu, 1 Jul 2021 12:06:33 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH v3 1/3] sched: Fix UCLAMP_FLAG_IDLE setting |
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On 06/30/21 15:45, Quentin Perret wrote: > Hi Qais, > > On Wednesday 30 Jun 2021 at 15:58:48 (+0100), Qais Yousef wrote: > > I just realized this needs > > > > if (clamp_id == UCLAMP_MAX) > > rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE; > > > > The code is only set for UCLAMP_MAX, so should be cleared for UCLAMP_MAX too. > > > > Though there's ugly overload here: > > > > if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE)) > > return; > > > > This check would fail prematurely if UCLAMP_MAX was reset before UCLAMP_MIN. > > The code before your change would reset both then do the clear. But now when we > > do it from here, we need to be more careful about that. > > Right, although this should all work fine as-is, I agree that relying on > the calling order is a bit dodgy and might cause issues in the long run. > > What do you think of this instead?
I can't objectively say one way is better than the other, this has the drawback of having to remember to clear the flag after each call to uclamp_rq_inc_id(). So it's pick your pain type of situation :-)
We can move the flag to struct uclamp_se. But this looks unnecessary churn to me..
Cheers
-- Qais Yousef
> > 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; > } > > task_rq_unlock(rq, p, &rf);
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