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

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Message-ID: <20090605063243.GC3872@in.ibm.com>
Date:	Fri, 5 Jun 2009 12:02:43 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	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 09:03:37AM +0300, Avi Kivity wrote:
> Balbir Singh wrote:
>>> I think so.  Given guarantees G1..Gn (0 <= Gi <= 1; sum(Gi) <= 1), 
>>> and a  cpu hog running in each group, how would the algorithm divide 
>>> resources?
>>>
>>>     
>>
>> As per the matrix calculation, but as soon as we reach an idle point,
>> we redistribute the b/w and start a new quantum so to speak, where all
>> groups are charged up to their hard limits.
>>
>> For your question, if there is a CPU hog running, it would be as per
>> the matrix calculation, since the system has no idle point during the
>> bandwidth period.
>>   
>
> So the groups with guarantees get a priority boost.  That's not a good  
> side effect.

That happens only in the presence of idle cycles when other groups [with or
without guarantees] have nothing useful to do. So how would that matter
since there is nothing else to run anyway ?

Regards,
Bharata.
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