linux-kernel - Re: [PATCH 2/2] sched: update runqueue clock before migrations away

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Date:	Wed, 18 Dec 2013 10:13:14 +0000
From:	Chris Redpath <chris.redpath@....com>
To:	"bsegall@...gle.com" <bsegall@...gle.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	"pjt@...gle.com" <pjt@...gle.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"alex.shi@...aro.org" <alex.shi@...aro.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Redpath <Chris.Redpath@....com>
Subject: Re: [PATCH 2/2] sched: update runqueue clock before migrations away

On 17/12/13 18:03, bsegall@...gle.com wrote:
> __synchronize_entity_decay will decay load_avg_contrib in order to
> figure out how much to remove from old_cfs_rq->blocked_load.
> update_entity_load_avg will update the underlying runnable_avg_sum/period that
> is used to update load_avg_contrib.
>
> (Normally we update runnable_avg_sum, which updates load_avg_contrib via
> __update_entity_load_avg_contrib. Here we go in the reverse direction
> because we don't hold the right rq locks at the right times.)
>

Thanks Ben, got it now. The only question remaining for me to figure out 
is if I need to include the missed tick time in the contrib decay or not 
- I definitely need to include it in the negative decay count we send 
through a migration. I'll go and check the places we use the removed 
load and update blocked load again.

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