linux-kernel - Re: [RFC -v3 PATCH 2/3] sched: add yield

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Date:	Wed, 5 Jan 2011 01:12:45 +0800
From:	Hillf Danton <dhillf@...il.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>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function

On Wed, Jan 5, 2011 at 1:08 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Wed, 2011-01-05 at 00:51 +0800, Hillf Danton wrote:
>> Where is the yield_to callback in the patch for RT schedule class?
>> If @p is RT, what could you do?
>
> RT guests are a pipe dream, you first need to get the hypervisor (kvm in
> this case) to be RT, which it isn't. Then you either need to very
> statically set-up the host and the guest scheduling constraints (not
> possible with RR/FIFO) or have a complete paravirt RT scheduler which
> communicates its requirements to the host.
>
Even guest is not RT, you could not prevent it from being preempted by
RT task which has nothing to do guests.
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