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

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Message-ID: <20101203133056.GF27994@linux.vnet.ibm.com>
Date:	Fri, 3 Dec 2010 19:00:57 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Rik van Riel <riel@...hat.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 Fri, Dec 03, 2010 at 02:23:39PM +0100, Peter Zijlstra wrote:
> Right, so another approach might be to simply swap the vruntime between
> curr and p.

Can't that cause others to stave? For ex: consider a cpu p0 having these tasks:

p0 ->  A0 B0 A1

A0/A1 have entered some sort of AB<->BA spin-deadlock, as a result A0 wants to
direct yield to A1 which wants to direct yield to A0. If we keep swapping their
runtimes, can't it starve B0?

- vatsa


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