linux-kernel - Re: [PATCH 1/7] sched: Introduce scale-invariant load tracking

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Date:	Fri, 10 Oct 2014 11:14:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Morten Rasmussen <morten.rasmussen@....com>, mingo@...hat.com,
	dietmar.eggemann@....com, pjt@...gle.com, bsegall@...gle.com,
	vincent.guittot@...aro.org, nicolas.pitre@...aro.org,
	mturquette@...aro.org, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] sched: Introduce scale-invariant load tracking

On Wed, Oct 08, 2014 at 08:50:07AM +0800, Yuyang Du wrote:
> Hi Morten,
> 
> Sorry for late jumping in.
> 
> The problem seems to be self-evident. But for the implementation to be
> equally attractive it needs to account for every freq change for every task,
> or anything less than that makes it less attractive.

I'm not entirely sure that is indeed required.

> But this should be very hard. Intel Architecture has limitation to capture all
> the freq changes in software and also the intel_pstate should have no
> notification.

So current Intel arch takes P-states as hints and then can mostly lower
their actual frequency, right? In this case still accounting at the
higher frequency is not a problem, the hardware conserves more power
than we know, but that's the right kind of error to have :-)

For the full automatic hardware, that's basically hardware without DVFS
capability so we should not bother at all and simply disable this
scaling.

> For every task, this makes the updating of the entire queue in load tracking
> more needed, so once again, ping maintainers for the rewrite patches, :)

Could you remind me what your latest version is; please reply to those
patches with a new email so that I can more conveniently locate it.
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