Date: Fri, 5 Jun 2009 13:27:55 +0800
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Avi Kivity <avi@redhat.com>
Cc: bharata@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
       Dhaval Giani <dhaval@linux.vnet.ibm.com>,
       Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
       Gautham R Shenoy <ego@in.ibm.com>,
       Srivatsa Vaddagiri <vatsa@in.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Pavel Emelyanov <xemul@openvz.org>, kvm@vger.kernel.org,
       Linux Containers <containers@lists.linux-foundation.org>,
       Herbert Poetzl <herbert@13thfloor.at>
Subject: Re: [RFC] CPU hard limits
Message-ID: <20090605052755.GE11755@balbir.in.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
References: <20090604053649.GA3701@in.ibm.com> <4A27BBCA.5020606@redhat.com> <20090605030309.GA3872@in.ibm.com> <4A28921C.6010802@redhat.com> <661de9470906042137u603e2997n80c270bf7f6191ad@mail.gmail.com> <4A28A2AB.3060108@redhat.com> <20090605044946.GA11755@balbir.in.ibm.com> <20090605051050.GB11755@balbir.in.ibm.com> <4A28AB67.7040800@redhat.com>
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* Avi Kivity <avi@redhat.com> [2009-06-05 08:21:43]:

> Balbir Singh wrote:
>>> But then there is no other way to make a *guarantee*, guarantees come
>>> at a cost of idling resources, no? Can you show me any other
>>> combination that will provide the guarantee and without idling the
>>> system for the specified guarantees?
>>>     
>>
>> OK, I see part of your concern, but I think we could do some
>> optimizations during design. For example if all groups have reached
>> their hard-limit and the system is idle, should we do start a new hard
>> limit interval and restart, so that idleness can be removed. Would
>> that be an acceptable design point?
>
> 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.

-- 
	Balbir
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