linux-kernel - Re: [RFC PATCH 2/3] sched: add yield

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Date:	Fri, 10 Dec 2010 09:55:59 -0500
From:	Rik van Riel <riel@...hat.com>
To:	vatsa@...ux.vnet.ibm.com
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Avi Kiviti <avi@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Anthony Liguori <aliguori@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 2/3] sched: add yield_to function

On 12/10/2010 03:39 AM, Srivatsa Vaddagiri wrote:
> On Thu, Dec 09, 2010 at 11:34:46PM -0500, Rik van Riel wrote:
>> On 12/03/2010 09:06 AM, Srivatsa Vaddagiri wrote:
>>> On Fri, Dec 03, 2010 at 03:03:30PM +0100, Peter Zijlstra wrote:
>>>> No, because they do receive service (they spend some time spinning
>>>> before being interrupted), so the respective vruntimes will increase, at
>>>> some point they'll pass B0 and it'll get scheduled.
>>>
>>> Is that sufficient to ensure that B0 receives its fair share (1/3 cpu in this
>>> case)?
>>
>> I have a rough idea for a simpler way to ensure
>> fairness.
>>
>> At yield_to time, we could track in the runqueue
>> structure that a task received CPU time (and on
>> the other runqueue that a task donated CPU time).
>>
>> The balancer can count time-given-to CPUs as
>> busier, and donated-time CPUs as less busy,
>> moving tasks away in the unlikely event that
>> the same task gets keeping CPU time given to
>> it.
>
> I think just capping donation (either on send side or receive side) may be more
> simpler here than to mess with load balancer logic.

Do you have any ideas on how to implement this in a simple
enough way that it may be acceptable upstream? :)

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