linux-kernel - Re: [PATCH 08/14] sched: add latency tracing for -deadline tasks.

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Date:	Wed, 20 Nov 2013 16:33:18 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
	oleg@...hat.com, fweisbec@...il.com, darren@...art.com,
	johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...il.com, liming.wang@...driver.com, jkacur@...hat.com,
	harald.gustafsson@...csson.com, vincent.guittot@...aro.org,
	bruce.ashfield@...driver.com
Subject: Re: [PATCH 08/14] sched: add latency tracing for -deadline tasks.

On Thu,  7 Nov 2013 14:43:42 +0100
Juri Lelli <juri.lelli@...il.com> wrote:


> +	/*
> +	 * Semantic is like this:
> +	 *  - wakeup tracer handles all tasks in the system, independently
> +	 *    from their scheduling class;
> +	 *  - wakeup_rt tracer handles tasks belonging to sched_dl and
> +	 *    sched_rt class;
> +	 *  - wakeup_dl handles tasks belonging to sched_dl class only.
> +	 */
> +	if ((wakeup_dl && !dl_task(p)) ||
> +	    (wakeup_rt && !dl_task(p) && !rt_task(p)) ||
> +	    (p->prio >= wakeup_prio || p->prio >= current->prio))
>  		return;
>  
>  	pc = preempt_count();
> @@ -486,7 +495,7 @@ probe_wakeup(void *ignore, struct task_struct *p, int success)
>  	arch_spin_lock(&wakeup_lock);
>  
>  	/* check for races. */
> -	if (!tracer_enabled || p->prio >= wakeup_prio)
> +	if (!tracer_enabled || (!dl_task(p) && p->prio >= wakeup_prio))
>  		goto out_locked;

We probably want to add a "tracing_dl" variable, and do the test like
this:

	if (!tracer_enabled || tracing_dl ||
	    (!dl_task(p) && p->prio >= wakeup_prio))

and for the first if statement too. Otherwise if two dl tasks are
running on two different CPUs, the second will override the first. Once
you start tracing a dl_task, you shouldn't bother tracing another task
until that one wakes up.

	if (dl_task(p))
		tracing_dl = 1;
	else
		tracing_dl = 0;

-- Steve
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