linux-kernel - Re: [PATCH 11/16] sched: add latency tracing for -deadline tasks.

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Message-ID: <1334178222.23924.304.camel@gandalf.stny.rr.com>
Date:	Wed, 11 Apr 2012 17:03:42 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
	cfriesen@...tel.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@...csson.com, liming.wang@...driver.com
Subject: Re: [PATCH 11/16] sched: add latency tracing for -deadline tasks.

On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote:
> From: Dario Faggioli <raistlin@...ux.it>
> 
> It is very likely that systems that wants/needs to use the new
> SCHED_DEADLINE policy also want to have the scheduling latency of
> the -deadline tasks under control.
> 
> For this reason a new version of the scheduling wakeup latency,
> called "wakeup_dl", is introduced.
> 
> As a consequence of applying this patch there will be three wakeup
> latency tracer:
>  * "wakeup", that deals with all tasks in the system;
>  * "wakeup_rt", that deals with -rt and -deadline tasks only;
>  * "wakeup_dl", that deals with -deadline tasks only.
> 
> Signed-off-by: Dario Faggioli <raistlin@...ux.it>
> Signed-off-by: Juri Lelli <juri.lelli@...il.com>
> ---
>  kernel/trace/trace_sched_wakeup.c |   41 ++++++++++++++++++++++++++++++++++++-
>  kernel/trace/trace_selftest.c     |   30 ++++++++++++++++----------
>  2 files changed, 58 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
> index e4a70c0..9c9b1be 100644
> --- a/kernel/trace/trace_sched_wakeup.c
> +++ b/kernel/trace/trace_sched_wakeup.c
> @@ -27,6 +27,7 @@ static int			wakeup_cpu;
>  static int			wakeup_current_cpu;
>  static unsigned			wakeup_prio = -1;
>  static int			wakeup_rt;
> +static int			wakeup_dl;
>  
>  static arch_spinlock_t wakeup_lock =
>  	(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
> @@ -420,6 +421,17 @@ probe_wakeup(void *ignore, struct task_struct *p, int success)
>  	if ((wakeup_rt && !rt_task(p)) ||
>  			p->prio >= wakeup_prio ||
>  			p->prio >= current->prio)

I don't think you meant to keep both if statements. Look above and
below ;-)

> +	/*
> +	 * 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;

Anyway, perhaps this should be broken up, as we don't want the double
test, that is, wakeup_rt and wakeup_dl are both checked. Perhaps do:

	if (wakeup_dl && !dl_task(p))
		return;
	else if (wakeup_rt && !dl_task(p) && !rt_task(p))
		return;

	if (p->prio >= wakeup_prio || p->prio >= current->prio)
		return;


-- Steve

>  
>  	pc = preempt_count();
> @@ -431,7 +443,7 @@ 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;
>  
>  	/* reset the trace */
> @@ -539,16 +551,25 @@ static int __wakeup_tracer_init(struct trace_array *tr)
>  


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