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Message-ID: <70837b44-4d21-9d70-d13b-2b6168fd02e3@redhat.com>
Date:   Tue, 4 Jul 2023 17:52:42 +0200
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Subject: Re: [RFC PATCH V3 4/6] sched/deadline: Introduce deadline servers
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To:     Valentin Schneider <vschneid@redhat.com>,
        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>,
        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>
References: <cover.1686239016.git.bristot@kernel.org>
 <e08a76013ff2b6a83028e8fdf3b8a6a0aa677d58.1686239016.git.bristot@kernel.org>
 <xhsmhpm5mw2gm.mognet@vschneid.remote.csb>
From:   Daniel Bristot de Oliveira <bristot@redhat.com>
In-Reply-To: <xhsmhpm5mw2gm.mognet@vschneid.remote.csb>
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Back from EOSS...

On 6/23/23 18:47, Valentin Schneider wrote:
> 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).

makes sense... I will check that in the v4.

> 
>> +	/* 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?

I think that the commend was added more as a check if it is correct... it seems it is.

Thanks Vale!
-- Daniel

> 
>>  	return p;
>>  }
>>  
>