Re: [PATCH v2] sched/uclamp: Avoid getting unreasonable ucalmp value when rq is idle

From: Peter Zijlstra
Date: Fri Jul 02 2021 - 08:00:54 EST

On Fri, Jul 02, 2021 at 12:54:21PM +0100, Qais Yousef wrote:
> Yep. How about the below?
> --->8---
> sched/uclamp: Ignore max aggregation if rq is idle
> When a task wakes up on an idle rq, uclamp_rq_util_with() would max
> aggregate with rq value. But since there is no task enqueued yet, the
> values are stale based on the last task that was running. When the new
> task actually wakes up and enqueued, then the rq uclamp values should
> reflect that of the newly woken up task effective uclamp values.
> This is a problem particularly for uclamp_max because it default to
> 1024. If a task p with uclamp_max = 512 wakes up, then max aggregation
> would ignore the capping that should apply when this task is enqueued,
> which is wrong.
> Fix that by ignoring max aggregation if the rq is idle since in that
> case the effective uclamp value of the rq will be the ones of the task
> that will wake up.
> --->8---

Much better, I've updated it. Thanks!