linux-kernel - Re: [RFC v2 PATCH 0/8] CFS Hard limits

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Date:	Wed, 30 Sep 2009 19:10:27 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	balbir@...ux.vnet.ibm.com
CC:	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>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Avi Kivity <avi@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Paul Menage <menage@...gle.com>,
	Mike Waychison <mikew@...gle.com>
Subject: Re: [RFC v2 PATCH 0/8] CFS Hard limits - v2

Balbir Singh wrote:
> * Pavel Emelyanov <xemul@...nvz.org> [2009-09-30 17:36:29]:
> 
>> Bharata B Rao wrote:
>>> Hi,
>>>
>>> Here is the v2 post of hard limits feature for CFS group scheduler. This
>>> RFC post mainly adds runtime borrowing feature and has a new locking scheme
>>> to protect CFS runtime related fields.
>>>
>>> It would be nice to have some comments on this set!
>> I have a question I'd like to ask before diving into the code.
>> Consider I'm a user, that has a 4CPUs box 2GHz each and I'd like
>> to create a container with 2CPUs 1GHz each. Can I achieve this
>> after your patches?
> 
> I don't think the GHz makes any sense, consider CPUs with frequency
> scaling. If I can scale from 1.6GHz to say 2.6GHz or 2GHz to 4GHz,
> what does it mean for hard limit control? Hard limits define control
> over existing bandwidth, anything else would be superficial and hard
> hard to get right for both developers and users.

Two numbers for configuring limits make even less sense OTOH ;)
By assigning 2GHz for 4GHz CPU I obviously want half of its power ;)
Please, see my reply to vatsa@ in this thread.
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