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From:   Valentin Schneider <vschneid@redhat.com>
To:     Daniel Bristot de Oliveira <bristot@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        linux-kernel@vger.kernel.org,
        Luca Abeni <luca.abeni@santannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
        Thomas Gleixner <tglx@linutronix.de>,
        Joel Fernandes <joel@joelfernandes.org>,
        Vineeth Pillai <vineeth@bitbyteword.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Daniel Bristot de Oliveira <bristot@kernel.org>
Subject: Re: [RFC PATCH V3 4/6] sched/deadline: Introduce deadline servers
In-Reply-To: <e08a76013ff2b6a83028e8fdf3b8a6a0aa677d58.1686239016.git.bristot@kernel.org>
References: <cover.1686239016.git.bristot@kernel.org>
 <e08a76013ff2b6a83028e8fdf3b8a6a0aa677d58.1686239016.git.bristot@kernel.org>
Date:   Fri, 23 Jun 2023 17:47:05 +0100
Message-ID: <xhsmhpm5mw2gm.mognet@vschneid.remote.csb>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On 08/06/23 17:58, Daniel Bristot de Oliveira wrote:
> @@ -2033,9 +2147,20 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
>  	struct task_struct *p;
>  
>  	p = pick_task_dl(rq);
> -	if (p)
> +	if (!p)
> +		return p;
> +
> +	/*
> +	 * XXX: re-check !dl_server, changed from v2 because of
> +	 * pick_next_task_dl change
> +	 */
> +	if (!dl_server(&p->dl))
>  		set_next_task_dl(rq, p, true);
>

Should this be

       if (!p->server)

instead? AFAICT dl_server(&p->dl) can never be true since there's no
pi_se-like link to the server via the dl_se, only via the task_struct, and
the server pick cannot return the server itself (as it's a pure sched_entity).

> +	/* XXX not quite right */
> +	if (hrtick_enabled(rq))
> +		start_hrtick_dl(rq, &p->dl);
> +

IIUC that got hauled out of set_next_task_dl() to cover the case where we
pick the server (+ the server pick) and want to more thoroughly enforce the
server's bandwidth. If so, what's the issue with starting the hrtick here?

>  	return p;
>  }
>