linux-kernel - Re: fair group scheduler not so fair?

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Message-ID: <483C4F5A.2010104@nortel.com>
Date:	Tue, 27 May 2008 12:13:46 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	vatsa@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, pj@....com,
	Balbir Singh <balbir@...ibm.com>,
	aneesh.kumar@...ux.vnet.ibm.com, dhaval@...ux.vnet.ibm.com
Subject: Re: fair group scheduler not so fair?

Srivatsa Vaddagiri wrote:

> But first, note that Groups "a" and "b" share bandwidth with all tasks
> in /dev/cgroup/tasks.

Ah, good point.  I've switched over to your group setup for testing.

> The following experimental patch (on top of 2.6.26-rc3 +
> http://programming.kicks-ass.net/kernel-patches/sched-smp-group-fixes/) seems 
> to fix the problem.

> Can you check if this makes a difference for you as well?

Initially it looked promising.  I put pid 2498 in group A, and pids 2499 
and 2500 in group B.  2498 got basically a full cpu, and the other two 
got 50% each.

However, I then moved pid 2499 from group B to group A, and the system 
got stuck in the following behaviour:

2498 cfriesen  20   0  3800  392  336 R 99.7  0.0   3:00.22 cat
2500 cfriesen  20   0  3800  392  336 R 66.7  0.0   1:39.10 cat
2499 cfriesen  20   0  3800  392  336 R 33.0  0.0   1:24.31 cat

I reproduced this a number of times.

Chris
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