Messages in this thread Patch in this message | | | From | Xuewen Yan <> | Subject | [PATCH v2] sched/uclamp: Avoid getting unreasonable ucalmp value when rq is idle | Date | Wed, 30 Jun 2021 22:12:04 +0800 |
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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 runnable task's UCLAMP_MAX; (2)the p's uc_eff_max < uc_rq_max.
As a result, 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.
When rq has UCLAMP_FLAG_IDLE flag, enqueuing the task will lift UCLAMP_FLAG_IDLE and set the rq clamp as the task's via uclamp_idle_reset(). It doesn't need to read the rq clamp. And it can also avoid the problems described above.
Fixes: 9d20ad7dfc9a ("sched/uclamp: Add uclamp_util_with()")
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
--- change v2: *add Fixes(Valentin Schneider); *ignore all rq clamp when idle (Valentin Schneider) --- kernel/sched/sched.h | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c80d42e9589b..14a41a243f7b 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2818,20 +2818,27 @@ 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)); - max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX)); + 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) + 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 -- 2.25.1
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