linux-kernel - Re: [Resend PATCH v8 0/4] sched: Rewrite runnable load and utilization average tracking

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Date:	Wed, 17 Jun 2015 21:06:17 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...nel.org, peterz@...radead.org,
	linux-kernel@...r.kernel.org, pjt@...gle.com, bsegall@...gle.com,
	morten.rasmussen@....com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, len.brown@...el.com,
	rafael.j.wysocki@...el.com, fengguang.wu@...el.com,
	srikar@...ux.vnet.ibm.com
Subject: Re: [Resend PATCH v8 0/4] sched: Rewrite runnable load and
 utilization average tracking

Hi Yuyang,

On Wed, Jun 17, 2015 at 11:11:01AM +0800, Yuyang Du wrote:
> Hi,
> 
> The sched_debug is informative, lets first give it some analysis.
> 
> The workload is 12 CPU hogging tasks (always runnable) and 1 dbench
> task doing fs ops (70% runnable) running at the same time.
> 
> Actually, these 13 tasks are in a task group /autogroup-9617, which
> has weight 1024.
> 
> So the 13 tasks at most can contribute to an average of 79 (=1024/13)
> 

[snip]

> So the problem is:
> 
> 1) The tasks in the workload have too small weight (only 79), because
>    they share a task group.
> 
> 2) Probably some "high" weight task even runnable a small time
>    contribute "big" to cfs_rq's load_avg.

Thank you for your analysis.

Some updates:

I created a task group /g and set /g/cpu.shares to 13312 (1024 * 13),
and then ran `stress --cpu 12` and `dbench 1` simultaneously in that
group. The situation is much better, only one CPU is not fully loaded,
and its utilization rate stays around 85%.

Regards,
Boqun

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