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

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Message-ID: <20090605053159.GB3872@in.ibm.com>
Date:	Fri, 5 Jun 2009 11:01:59 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.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 01:27:55PM +0800, Balbir Singh wrote:
> * Avi Kivity <avi@...hat.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.

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 ?

Regards,
Bharata.
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