linux-kernel - Re: [PATCH 17/18] sched: Tracepoint task movement

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Message-ID: <20131210084257.GD11295@suse.de>
Date:	Tue, 10 Dec 2013 08:42:57 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Thorlton <athorlton@....com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Drew Jones <drjones@...hat.com>
Subject: Re: [PATCH 17/18] sched: Tracepoint task movement

On Mon, Dec 09, 2013 at 01:54:51PM -0500, Rik van Riel wrote:
> On 12/09/2013 02:09 AM, Mel Gorman wrote:
> > move_task() is called from move_one_task and move_tasks and is an
> > approximation of load balancer activity. We should be able to track
> > tasks that move between CPUs frequently. If the tracepoint included node
> > information then we could distinguish between in-node and between-node
> > traffic for load balancer decisions. The tracepoint allows us to track
> > local migrations, remote migrations and average task migrations.
> > 
> > Signed-off-by: Mel Gorman <mgorman@...e.de>
> 
> Does this replicate the task_sched_migrate_task tracepoint in
> set_task_cpu() ?
> 

There is significant overlap but bits missing. We do not necessarily know
where the task was previously running and whether this is a local->remote
migration. We also cannot tell the difference between load balancer activity,
numa balancing and try_to_wake_up. Still, you're right, this patch is not
painting a full picture either. I'll drop it for now and look at improving
the existing task_sched_migrate_task tracepoint.

-- 
Mel Gorman
SUSE Labs
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