linux-kernel - Re: [patch 13/16] sched: update_cfs

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Message-ID: <5060B9C2.5040200@cs.tu-berlin.de>
Date:	Mon, 24 Sep 2012 21:51:30 +0200
From:	"Jan H. Schönherr" 
	<schnhrr@...tu-berlin.de>
To:	pjt@...gle.com
CC:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Venki Pallipadi <venki@...gle.com>,
	Ben Segall <bsegall@...gle.com>,
	Mike Galbraith <efault@....de>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [patch 13/16] sched: update_cfs_shares at period edge

Am 23.08.2012 16:14, schrieb pjt@...gle.com:
> From: Paul Turner <pjt@...gle.com>
> 
> Now that our measurement intervals are small (~1ms) we can amortize the posting
> of update_shares() to be about each period overflow.  This is a large cost
> saving for frequently switching tasks.

[snip]

> @@ -1181,6 +1181,7 @@ static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq, int force_update)
>  	}
>  
>  	__update_cfs_rq_tg_load_contrib(cfs_rq, force_update);
> +	update_cfs_shares(cfs_rq);
>  }

Here a call to update_cfs_shares() gets added. Doesn't that make the call to
update_cfs_shares() in __update_blocked_averages_cpu() superfluous?


Function pasted here for reference:

static void __update_blocked_averages_cpu(struct task_group *tg, int cpu)
{
	struct sched_entity *se = tg->se[cpu];
	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu];

	/* throttled entities do not contribute to load */
	if (throttled_hierarchy(cfs_rq))
		return;

	update_cfs_rq_blocked_load(cfs_rq, 1);

	if (se) {
		update_entity_load_avg(se, 1);
		/*
		 * We can pivot on the runnable average decaying to zero for
		 * list removal since the parent average will always be >=
		 * child.
		 */
		if (se->avg.runnable_avg_sum)
			update_cfs_shares(cfs_rq);
		else
			list_del_leaf_cfs_rq(cfs_rq);
	} else {
		struct rq *rq = rq_of(cfs_rq);
		update_rq_runnable_avg(rq, rq->nr_running);
	}
}


Regards
Jan
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