Messages in this thread | | | Date | Thu, 10 Jun 2021 11:00:39 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH] sched: Fix UCLAMP_FLAG_IDLE setting |
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On 06/09/21 14:33, Quentin Perret wrote: > The UCLAMP_FLAG_IDLE flag is set on a runqueue when dequeueing the last > active task to maintain the last uclamp.max and prevent blocked util > from suddenly becoming visible. > > However, there is an asymmetry in how the flag is set and cleared which > can lead to having the flag set whilst there are active task on the rq. > Specifically, the flag is set in the uclamp_rq_inc() path, which is > called at enqueue time, but cleared in the uclamp_rq_dec_id() which is
It is actually the other way around. It is cleared in uclamp_rq_inc() and set in uclamp_rq_dec_id().
> called both when dequeueing and task _and_ during cgroup migrations.
Is it cgroup migrations or when cgroup uclamp values are updated you mean?
It is worth being direct and mention that uclamp_update_active() will perform uclamp_rq_dec/inc_id() when the cgroup uclamp values are updated, which would end up with the flag set but not cleared in this path.
> > Fix this by setting the flag in the uclamp_rq_inc_id() path to ensure > things remain symmetrical. > > Reported-by: Rick Yiu <rickyiu@google.com> > Signed-off-by: Quentin Perret <qperret@google.com> > ---
With the commit message fixed.
Reviewed-by: Qais Yousef <qais.yousef@arm.com>
Thanks!
-- Qais Yousef
> kernel/sched/core.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 5226cc26a095..3b213402798e 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -980,6 +980,7 @@ 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); > } > > @@ -1252,10 +1253,6 @@ 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) > -- > 2.32.0.272.g935e593368-goog >
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