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

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Date:	Thu, 04 Jun 2009 23:09:22 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	balbir@...ux.vnet.ibm.com
CC:	Avi Kivity <avi@...hat.com>, bharata@...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

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?

The example given was two 10% guaranteed groups and one best-effort
group.  Why would this require idling resources?

If I have a hog in each group, the requirements would be met if the
groups got 33, 33, and 33.  (Or 10/10/80, for that matter.)  If the
second and third groups go idle, why not let the first group use 100% of
the cpu?

The only hard restriction is that the sum of the guarantees must be less
than 100%.

Chris
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