Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | Re: [PATCH] sched/uclamp: Fix getting unreasonable ucalmp_max when rq is idle | Date | Tue, 29 Jun 2021 14:50:21 +0100 |
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+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()")
?
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:
--- 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)); +out: /* * Since CPU's {min,max}_util clamps are MAX aggregated considering * RUNNABLE tasks with _different_ clamps, we can end up with an
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