Re: [RFC -v2 PATCH 2/3] sched: add yield_to function

[Rik van Riel]

On 12/28/2010 12:54 AM, Mike Galbraith wrote:
> On Mon, 2010-12-20 at 17:04 +0100, Mike Galbraith wrote:
> > On Mon, 2010-12-20 at 10:40 -0500, Rik van Riel wrote:
> > > On 12/17/2010 02:15 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)?
> > > >
> > > > Even swapping vruntimes in the same cfs_rq is dangerous as hell, because
> > > > one party is going backward.
> > >
> > > I just realized the answer to this question.
> > >
> > > We only give cpu time to tasks that are runnable, but not
> > > currently running.  That ensures one task cannot block others
> > > from running by having time yielded to it constantly.
> >
> > Hm.  Don't think that will 100% sure prevent clock stoppage, because the
> > running task doesn't necessarily advance min_vruntime.
> >
> > What about something like the below instead?  It compiles, but may eat
> > your first born child.
>
> (either it's christmas, or nobody cares to try it.  ho ho hum:)

It's christmas.

I've replaced my original patch with your patch in my
series, just haven't gotten around to running Avi's
latest test on it yet :)

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