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

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Message-ID: <20090605081651.GD3872@in.ibm.com>
Date:	Fri, 5 Jun 2009 13:46:51 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Balbir Singh <balbir@...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 05, 2009 at 09:01:50AM +0300, Avi Kivity wrote:
> Bharata B Rao wrote:
>>
>> But could there be client models where you are required to strictly
>> adhere to the limit within the bandwidth and not provide more (by advancing
>> the bandwidth period) in the presence of idle cycles ?
>>   
>
> That's the limit part.  I'd like to be able to specify limits and  
> guarantees on the same host and for the same groups; I don't think that  
> works when you advance the bandwidth period.
>
> I think we need to treat guarantees as first-class goals, not something  
> derived from limits (in fact I think guarantees are more useful as they  
> can be used to provide SLAs).

I agree that guarantees are important, but I am not sure about

1. specifying both limits and guarantees for groups and
2. not deriving guarantees from limits.

Guarantees are met by some form of throttling or limiting and hence I think
limiting should drive the guarantees.

Regards,
Bharata.
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