Messages in this thread | | | Date | Thu, 10 Jun 2021 10:27:32 +0000 | From | Quentin Perret <> | Subject | Re: [PATCH] sched: Fix UCLAMP_FLAG_IDLE setting |
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On Thursday 10 Jun 2021 at 11:00:39 (+0100), Qais Yousef wrote: > 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.
Yep, that's the problematic 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.
Ack, this commit message is a mess, I'll rewrite.
> Reviewed-by: Qais Yousef <qais.yousef@arm.com>
Thanks! Quentin
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