linux-kernel - Re: [PATCH v3 1/3] sched: Fix UCLAMP_FLAG

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Message-ID: <YN2T1qnalRUKNcXt@google.com>
Date:   Thu, 1 Jul 2021 10:07:18 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Qais Yousef <qais.yousef@....com>
Cc:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rickyiu@...gle.com, wvw@...gle.com,
        patrick.bellasi@...bug.net, xuewen.yan94@...il.com,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 1/3] sched: Fix UCLAMP_FLAG_IDLE setting

On Wednesday 30 Jun 2021 at 15:45:14 (+0000), Quentin Perret wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b094da4c5fea..c0b999a8062a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -980,7 +980,6 @@ static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
>         if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
>                 return;
> 
> -       rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
>         WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
>  }
> 
> @@ -1253,6 +1252,10 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
> 
>         for_each_clamp_id(clamp_id)
>                 uclamp_rq_inc_id(rq, p, clamp_id);
> +
> +       /* Reset clamp idle holding when there is one RUNNABLE task */
> +       if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
> +               rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
>  }
> 
>  static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
> @@ -1300,6 +1303,13 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
>         if (p->uclamp[clamp_id].active) {
>                 uclamp_rq_dec_id(rq, p, clamp_id);
>                 uclamp_rq_inc_id(rq, p, clamp_id);
> +
> +               /*
> +                * Make sure to clear the idle flag if we've transiently reached
> +                * 0 uclamp active tasks on the rq.
> +                */
> +               if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
> +                       rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;

Bah, now that I had coffee I realize this has the exact same problem.
Let me look at this again ...