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Date: Tue, 13 May 2014 09:36:20 -0400
From: Rik van Riel <riel@redhat.com>
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To: Peter Zijlstra <peterz@infradead.org>,
        Michael wang <wangyun@linux.vnet.ibm.com>
CC: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Mike Galbraith <efault@gmx.de>, Alex Shi <alex.shi@linaro.org>,
        Paul Turner <pjt@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Lezcano <daniel.lezcano@linaro.org>
Subject: Re: [ISSUE] sched/cgroup: Does cpu-cgroup still works fine nowadays?
References: <537192D3.5030907@linux.vnet.ibm.com> <20140513094737.GU30445@twins.programming.kicks-ass.net>
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On 05/13/2014 05:47 AM, Peter Zijlstra wrote:
> On Tue, May 13, 2014 at 11:34:43AM +0800, Michael wang wrote:
>> During our testing, we found that the cpu.shares doesn't work as
>> expected, the testing is:
>>
> 
> /me zaps all the kvm nonsense as that's non reproducable and only serves
> to annoy.
> 
> Pro-tip: never use kvm to report cpu-cgroup issues.
> 
>> So is this results expected (I really do not think so...)?
>>
>> Or that imply the cpu-cgroup got some issue to be fixed?
> 
> So what I did (WSM-EP 2x6x2):
> 
> mount none /cgroup -t cgroup -o cpu
> mkdir -p /cgroup/a
> mkdir -p /cgroup/b
> mkdir -p /cgroup/c
> 
> echo $$ > /cgroup/a/tasks ; for ((i=0; i<12; i++)) ; do A.sh & done
> echo $$ > /cgroup/b/tasks ; for ((i=0; i<12; i++)) ; do B.sh & done
> echo $$ > /cgroup/c/tasks ; for ((i=0; i<12; i++)) ; do C.sh & done
> 
> echo 2048 > /cgroup/c/cpu.shares
> 
> Where [ABC].sh are spinners:

I suspect the "are spinners" is key.

Infinite loops can run all the time, while dbench spends a lot of
its time waiting for locks. That waiting may interfere with getting
as much CPU as it wants.

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