linux-kernel - Re: [RFC -v2 PATCH 2/3] sched: add yield

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Date:	Sat, 18 Dec 2010 20:13:49 +0100
From:	Mike Galbraith <mgalbraith@...e.de>
To:	Avi Kivity <avi@...hat.com>
Cc:	Rik van Riel <riel@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [RFC -v2 PATCH 2/3] sched: add yield_to function

On Sat, 2010-12-18 at 19:08 +0200, Avi Kivity wrote:
> On 12/17/2010 09:15 AM, Mike Galbraith wrote:
> > BTW, with this vruntime donation thingy, what prevents a task from
> > forking off accomplices who do nothing but wait for a wakeup and
> > yield_to(exploit)?
> >
> 
> What's the difference between that and forking off accomplices who 
> run(exploit) directly?

The clock still advances.  What I described is a clock stopper.

> Many threads dominating the scheduler has been solved by group 
> scheduling.  We need to make sure directed yield doesn't violate that, 
> but I don't see new problems.

Let it become possible to stop clocks, and you surely will :)

	-Mike


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