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Date:   Fri, 26 Jul 2019 12:18:19 +0200
From:   luca abeni <luca.abeni@santannapisa.it>
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <Valentin.Schneider@arm.com>,
        Qais Yousef <Qais.Yousef@arm.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] sched/deadline: Use return value of SCHED_WARN_ON()
 in bw accounting
Message-ID: <20190726121819.32be6fb1@sweethome>
In-Reply-To: <20190726082756.5525-6-dietmar.eggemann@arm.com>
References: <20190726082756.5525-1-dietmar.eggemann@arm.com>
        <20190726082756.5525-6-dietmar.eggemann@arm.com>
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Hi Dietmar,

On Fri, 26 Jul 2019 09:27:56 +0100
Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:

> To make the decision whether to set rq or running bw to 0 in underflow
> case use the return value of SCHED_WARN_ON() rather than an extra if
> condition.

I think I tried this at some point, but if I remember well this
solution does not work correctly when SCHED_DEBUG is not enabled.


			Luca


> 
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> ---
>  kernel/sched/deadline.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index a9cb52ceb761..66c594b5507e 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -95,8 +95,7 @@ void __sub_running_bw(u64 dl_bw, struct dl_rq
> *dl_rq) 
>  	lockdep_assert_held(&(rq_of_dl_rq(dl_rq))->lock);
>  	dl_rq->running_bw -= dl_bw;
> -	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
> -	if (dl_rq->running_bw > old)
> +	if (SCHED_WARN_ON(dl_rq->running_bw > old)) /* underflow */
>  		dl_rq->running_bw = 0;
>  	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
>  	cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
> @@ -119,8 +118,7 @@ void __sub_rq_bw(u64 dl_bw, struct dl_rq *dl_rq)
>  
>  	lockdep_assert_held(&(rq_of_dl_rq(dl_rq))->lock);
>  	dl_rq->this_bw -= dl_bw;
> -	SCHED_WARN_ON(dl_rq->this_bw > old); /* underflow */
> -	if (dl_rq->this_bw > old)
> +	if (SCHED_WARN_ON(dl_rq->this_bw > old)) /* underflow */
>  		dl_rq->this_bw = 0;
>  	SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
>  }