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

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Message-ID: <20090605030309.GA3872@in.ibm.com>
Date:	Fri, 5 Jun 2009 08:33:10 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.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

On Thu, Jun 04, 2009 at 03:19:22PM +0300, Avi Kivity wrote:
> Bharata B Rao wrote:
>> 2. Need for hard limiting CPU resource
>> --------------------------------------
>> - Pay-per-use: In enterprise systems that cater to multiple clients/customers
>>   where a customer demands a certain share of CPU resources and pays only
>>   that, CPU hard limits will be useful to hard limit the customer's job
>>   to consume only the specified amount of CPU resource.
>> - In container based virtualization environments running multiple containers,
>>   hard limits will be useful to ensure a container doesn't exceed its
>>   CPU entitlement.
>> - Hard limits can be used to provide guarantees.
>>   
> How can hard limits provide guarantees?
>
> Let's take an example where I have 1 group that I wish to guarantee a  
> 20% share of the cpu, and anther 8 groups with no limits or guarantees.
>
> One way to achieve the guarantee is to hard limit each of the 8 other  
> groups to 10%; the sum total of the limits is 80%, leaving 20% for the  
> guarantee group. The downside is the arbitrary limit imposed on the  
> other groups.

This method sounds very similar to the openvz method:
http://wiki.openvz.org/Containers/Guarantees_for_resources

>
> 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 ?

Regards,
Bharata.
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