Date: Wed, 17 Jun 2015 21:06:17 +0800
From: Boqun Feng <boqun.feng@gmail.com>
To: Yuyang Du <yuyang.du@intel.com>
Cc: mingo@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org,
        pjt@google.com, bsegall@google.com, morten.rasmussen@arm.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        len.brown@intel.com, rafael.j.wysocki@intel.com,
        fengguang.wu@intel.com, srikar@linux.vnet.ibm.com
Subject: Re: [Resend PATCH v8 0/4] sched: Rewrite runnable load and
 utilization average tracking
Message-ID: <20150617130617.GB7154@fixme-laptop.cn.ibm.com>
References: <1434396367-27979-1-git-send-email-yuyang.du@intel.com>
 <20150617030650.GB5695@fixme-laptop.cn.ibm.com>
 <20150617051501.GA7154@fixme-laptop.cn.ibm.com>
 <20150617031101.GC1244@intel.com>
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Hi Yuyang,

On Wed, Jun 17, 2015 at 11:11:01AM +0800, Yuyang Du wrote:
> Hi,
>=20
> The sched_debug is informative, lets first give it some analysis.
>=20
> The workload is 12 CPU hogging tasks (always runnable) and 1 dbench
> task doing fs ops (70% runnable) running at the same time.
>=20
> Actually, these 13 tasks are in a task group /autogroup-9617, which
> has weight 1024.
>=20
> So the 13 tasks at most can contribute to an average of 79 (=3D1024/13)
>=20

[snip]

> So the problem is:
>=20
> 1) The tasks in the workload have too small weight (only 79), because
>    they share a task group.
>=20
> 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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