linux-kernel - Re: [RFC PATCH 03/16 v3] How CC accrues with run queue change and time

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Date:	Tue, 3 Jun 2014 14:12:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...hat.com, rafael.j.wysocki@...el.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	arjan.van.de.ven@...el.com, len.brown@...el.com,
	alan.cox@...el.com, mark.gross@...el.com, pjt@...gle.com,
	bsegall@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, rajeev.d.muralidhar@...el.com,
	vishwesh.m.rudramuni@...el.com, nicole.chalhoub@...el.com,
	ajaya.durg@...el.com, harinarayanan.seshadri@...el.com,
	jacob.jun.pan@...ux.intel.com, fengguang.wu@...el.com
Subject: Re: [RFC PATCH 03/16 v3] How CC accrues with run queue change and
 time

On Fri, May 30, 2014 at 02:35:59PM +0800, Yuyang Du wrote:
> It is natural to use task concurrency (running tasks in the rq) as load
> indicator. We calculate CC for task concurrency by two steps:
> 
> 1) Divide continuous time into periods of time, and average task concurrency
> in period, for tolerating the transient bursts:
> 
> a = sum(concurrency * time) / period
> 
> 2) Exponentially decay past periods, and synthesize them all, for hysteresis
> to load drops or resilience to load rises (let f be decaying factor, and a_x
> the xth period average since period 0):
> 
> s = a_n + f^1 * a_n-1 + f^2 * a_n-2 +, ..., + f^(n-1) * a_1 + f^n * a_0
> 
> To sum up, CPU CC is 1) decayed average run queue length, or 2) run-queue-lengh-
> weighted CPU utilization.

why!? what benefit does it have over utilization.

Also, not a mention of dvfs or how that would impact things.

> Signed-off-by: Yuyang Du <yuyang.du@...el.com>
> ---
>  kernel/sched/fair.c |  255 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 255 insertions(+)

And not a single word on why you cannot use the existing per-task
accounting infrastructure and not a single attempt to merge the two.



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