linux-kernel - Re: [PATCH] sched/deadline: Zero out positive runtime after throttling constrained tasks

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Date:   Thu, 11 May 2017 15:20:39 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     Xunlei Pang <xlpang@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH] sched/deadline: Zero out positive runtime after
 throttling constrained tasks

Hi,

On 10/05/17 21:03, Xunlei Pang wrote:
> When a contrained task is throttled by dl_check_constrained_dl(),
> it may carry the remaining positive runtime, as a result when
> dl_task_timer() fires and calls replenish_dl_entity(), it will
> not be replenished correctly due to the positive dl_se->runtime.
> 
> This patch assigns its runtime to 0 if positive after throttling.
> 
> Fixes: df8eac8cafce ("sched/deadline: Throttle a constrained deadline task activated after the deadline)
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
> ---
>  kernel/sched/deadline.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index a2ce590..d3d291e 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -723,6 +723,8 @@ static inline void dl_check_constrained_dl(struct sched_dl_entity *dl_se)
>  		if (unlikely(dl_se->dl_boosted || !start_dl_timer(p)))
>  			return;
>  		dl_se->dl_throttled = 1;
> +		if (dl_se->runtime > 0)
> +			dl_se->runtime = 0;
>  	}

Looks good to me. Although, we could alternatively add a flag and use
that in replenish_dl_entity() to reset runtime (as we do for dl_yielded).

Flags need refactoring, though.

Thanks,

- Juri