Message-ID: <4D0F78DF.9010908@redhat.com>
Date: Mon, 20 Dec 2010 10:40:15 -0500
From: Rik van Riel <riel@redhat.com>
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To: Mike Galbraith <mgalbraith@suse.de>
CC: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Avi Kiviti <avi@redhat.com>,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Chris Wright <chrisw@sous-sol.org>
Subject: Re: [RFC -v2 PATCH 2/3] sched: add yield_to function
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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.
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