linux-kernel - Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average tracking

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Date:	Tue, 29 Jul 2014 09:53:44 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>,
	arjan.van.de.ven@...el.com, Len Brown <len.brown@...el.com>,
	rafael.j.wysocki@...el.com, alan.cox@...el.com,
	"Gross, Mark" <mark.gross@...el.com>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>
Subject: Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average
 tracking

On Tue, Jul 29, 2014 at 11:39:11AM +0200, Peter Zijlstra wrote:
> > > For task, assuming its load.weight does not change much, yes, we can. But in theory, task's
> > 
> > I would even say that the load_avg of a task should not be impacted by
> > an old priority value. Once, the priority of a task is changed, we
> > should only take into account this new priority to weight the load_avg
> > of the task
> 
> So for tasks I would immediately agree, and I think for groups too,
> seeing how the group weight is based off of this avg, if you then
> include the old weight we'll get a feedback loop. This might not be
> desired as it would counteract the SMP movement of tasks.

Including the old weight can we get the *right* feedback. Because say until
weight is changed, we are balanced, changed weight leads to imbalance. Without
old weight, the imbalance is multiplied by the history, like we have never been
balanced.
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