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

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Date:	Fri, 05 Jun 2009 06:33:48 +0300
From:	Avi Kivity <avi@...hat.com>
To:	bharata@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...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

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.

#!/usr/bin/python

def calculate_limits(g, R):
    N = len(g)
    if N == 1:
        return [R]

    s = sum([R - gi for gi in g])
    return [(s - (R - gi) - (N - 2) * (R - gi)) / (N - 1)
            for gi in g]

import sys
print calculate_limits([float(x) for x in sys.argv[1:]], 100)

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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