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

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Message-ID: <4CFA3BE7.4050905@redhat.com>
Date:	Sat, 04 Dec 2010 08:02:31 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	vatsa@...ux.vnet.ibm.com, 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 12/03/2010 04:23 PM, Peter Zijlstra wrote:
> On Fri, 2010-12-03 at 19:40 +0530, Srivatsa Vaddagiri wrote:
>> On Fri, Dec 03, 2010 at 07:36:07PM +0530, 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)?
>>
>> Hmm perhaps yes, althought at cost of tons of context switches, which would be
>> nice to minimize on?
>
> Don't care, as long as the guys calling yield_to() pay for that time its
> their problem.

Also, the context switches are cheaper than spinning
entire time slices on spinlocks we're not going to get
(because the VCPU holding the lock is not running).

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