linux-kernel - Re: [PATCH v5 09/12] sched: add usage_load

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Date:	Mon, 15 Sep 2014 20:15:41 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"efault@....de" <efault@....de>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>
Subject: Re: [PATCH v5 09/12] sched: add usage_load_avg

On Tue, Aug 26, 2014 at 12:06:52PM +0100, Vincent Guittot wrote:
> Add new statistics which reflect the average time a task is running on the
> CPU and the sum of the tasks' running on a runqueue. The latter is named
> usage_avg_contrib.
> 
> This patch is based on the usage metric that was proposed in the 1st
> versions of the per-entity load tracking patchset but that has be removed
> afterward. This version differs from the original one in the sense that it's
> not linked to task_group.
> 
> The rq's usage_avg_contrib will be used to check if a rq is overloaded or not
> instead of trying to compute how many task a group of CPUs can handle
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

I should have read this patch before I did almost the same patch for as
part a series to introduce scale-invariance which I am about to post :(

The only difference I see is slightly different naming and that, AFAICT,
task group usage is not accounted for in this patch. Can we add the
support for task groups as well? I can provide a patch based on this one
if you want.

Also, since more than half this patch comes directly from PJT's original
patch I would add "by Paul Turner <pjt@...gle.com>" somewhere in the
text above.

[...]

> +static inline void __update_task_entity_usage(struct sched_entity *se)
> +{
> +	u32 contrib;
> +
> +	/* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
> +	contrib = se->avg.running_avg_sum * scale_load_down(SCHED_LOAD_SCALE);
> +	contrib /= (se->avg.runnable_avg_period + 1);
> +	se->avg.usage_avg_contrib = scale_load(contrib);
> +}
> +
> +static long __update_entity_usage_avg_contrib(struct sched_entity *se)
> +{
> +	long old_contrib = se->avg.usage_avg_contrib;
> +
> +	if (entity_is_task(se))
> +		__update_task_entity_usage(se);

Groups are never updated?

As said above. I have code that does it.

Morten

> +
> +	return se->avg.usage_avg_contrib - old_contrib;
> +}
> +

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