Re: [RFC -v3 PATCH 2/3] sched: add yield_to function

From: Peter Zijlstra
Date: Tue Jan 04 2011 - 12:22:05 EST

On Wed, 2011-01-05 at 01:12 +0800, Hillf Danton wrote:
> On Wed, Jan 5, 2011 at 1:08 AM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> 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.

Sure, but yield_to() being a NOP for RT tasks is perfectly fine. Pretty
much all yield*() usage is a bug anyway.
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