Messages in this thread | | | From | Xuewen Yan <> | Date | Wed, 30 Jun 2021 09:24:12 +0800 | Subject | Re: [PATCH] sched/uclamp: Fix getting unreasonable ucalmp_max when rq is idle |
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On Tue, Jun 29, 2021 at 9:50 PM Valentin Schneider <valentin.schneider@arm.com> wrote: > > > +Cc Patrick's current address > > On 18/06/21 15:23, Xuewen Yan wrote: > > From: Xuewen Yan <xuewen.yan@unisoc.com> > > > > Now in uclamp_rq_util_with(), when the task != NULL, the uclamp_max as following: > > uc_rq_max = rq->uclamp[UCLAMP_MAX].value; > > uc_eff_max = uclamp_eff_value(p, UCLAMP_MAX); > > uclamp_max = max{uc_rq_max, uc_eff_max}; > > > > Consider the following scenario: > > (1)the rq is idle, the uc_rq_max is last task's UCLAMP_MAX; > > (2)the p's uc_eff_max < uc_rq_max. > > > > The result is the uclamp_max = uc_rq_max instead of uc_eff_max, it is unreasonable. > > > > The scenario often happens in find_energy_efficient_cpu(), when the task has smaller UCLAMP_MAX. > > > > Inserts whether the rq is idle in the uclamp_rq_util_with(). > > > > Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com> > > --- > > kernel/sched/sched.h | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > > index a189bec13729..0feef6af89f2 100644 > > --- a/kernel/sched/sched.h > > +++ b/kernel/sched/sched.h > > @@ -2550,7 +2550,10 @@ unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util, > > > > if (p) { > > min_util = max(min_util, uclamp_eff_value(p, UCLAMP_MIN)); > > - max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX)); > > + if (rq->uclamp_flags & UCLAMP_FLAG_IDLE) > > + max_util = uclamp_eff_value(p, UCLAMP_MAX); > > + else > > + max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX)); > > That makes sense to me - enqueuing the task will lift UCLAMP_FLAG_IDLE and > set the rq clamp as the task's via uclamp_idle_reset(). > > Does this want a > > Fixes: 9d20ad7dfc9a ("sched/uclamp: Add uclamp_util_with()") > > ?
Yes,add it.
> > Also, when we have UCLAMP_FLAG_IDLE, we don't even need to read the rq max > - and I'm pretty sure the same applies to the rq min. What about something like:
Good idea, I'll try it in V2.
> > --- > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 6510f0a46789..a2c6f6ae6392 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -2833,23 +2833,27 @@ static __always_inline > unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util, > struct task_struct *p) > { > - unsigned long min_util; > - unsigned long max_util; > + unsigned long min_util = 0; > + unsigned long max_util = 0; > > if (!static_branch_likely(&sched_uclamp_used)) > return util; > > - min_util = READ_ONCE(rq->uclamp[UCLAMP_MIN].value); > - max_util = READ_ONCE(rq->uclamp[UCLAMP_MAX].value); > - > if (p) { > - min_util = max(min_util, uclamp_eff_value(p, UCLAMP_MIN)); > + min_util = uclamp_eff_value(p, UCLAMP_MIN); > + max_util = uclamp_eff_value(p, UCLAMP_MAX); > + > + /* > + * Ignore last runnable task's max clamp, as this task will > + * reset it. Similarly, no need to read the rq's min clamp. > + */ > if (rq->uclamp_flags & UCLAMP_FLAG_IDLE) > - max_util = uclamp_eff_value(p, UCLAMP_MAX); > - else > - max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX)); > + goto out; > } > > + min_util = max_t(unsigned long, min_util, READ_ONCE(rq->uclamp[UCLAMP_MIN].value)); > + max_util = max_t(unsigned long, max_util, READ_ONCE(rq->uclamp[UCLAMP_MAX].value));
Is it necessary to use max_t here? although it is not the main problem...
> +out: > /* > * Since CPU's {min,max}_util clamps are MAX aggregated considering > * RUNNABLE tasks with _different_ clamps, we can end up with an
Thanks! xuewen
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