linux-kernel - Re: [RFC] CPU hard limits

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Message-ID: <661de9470906042137u603e2997n80c270bf7f6191ad@mail.gmail.com>
Date:	Fri, 5 Jun 2009 12:37:17 +0800
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	bharata@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pavel Emelyanov <xemul@...nvz.org>, kvm@...r.kernel.org,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Herbert Poetzl <herbert@...hfloor.at>
Subject: Re: [RFC] CPU hard limits

On Fri, Jun 5, 2009 at 11:33 AM, Avi Kivity <avi@...hat.com> wrote:
> Bharata B Rao wrote:
>>>
>>> Another way is to place the 8 groups in a container group, and limit
>>>  that to 80%. But that doesn't work if I want to provide guarantees to
>>>  several groups.
>>>
>>
>> Hmm why not ? Reduce the guarantee of the container group and provide
>> the same to additional groups ?
>>
>
> This method produces suboptimal results:
>
> $ cgroup-limits 10 10 0
> [50.0, 50.0, 40.0]
>
> I want to provide two 10% guaranteed groups and one best-effort group.
>  Using the limits method, no group can now use more than 50% of the
> resources.  However, having the first group use 90% of the resources does
> not violate any guarantees, but it not allowed by the solution.
>

How, it works out fine in my calculation

50 + 40 for G2 and G3, make sure that G1 gets 10%, since others are
limited to 90%
50 + 40 for G1 and G3, make sure that G2 gets 10%, since others are
limited to 90%
50 + 50 for G1 and G2, make sure that G3 gets 0%, since others are
limited to 100%

Now if we really have zeros, I would recommend using

cgroup-limits 10 10 and you'll see that you'll get 90, 90 as output.

Adding zeros to the calcuation is not recommended. Does that help?

Balbir
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