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

From: Tommaso Cucinotta
Date: Tue Jan 04 2011 - 18:38:59 EST

Il 04/01/2011 19:15, Dario Faggioli ha scritto:

-------- Forwarded Message --------
From: Peter Zijlstra<a.p.zijlstra@xxxxxxxxx>
To: Rik van Riel<riel@xxxxxxxxxx>
Cc: Hillf Danton<dhillf@xxxxxxxxx>,kvm@xxxxxxxxxxxxxxx,
linux-kernel@xxxxxxxxxxxxxxx, Avi Kiviti<avi@xxxxxxxxxx>, Srivatsa
Vaddagiri<vatsa@xxxxxxxxxxxxxxxxxx>, Mike Galbraith<efault@xxxxxx>,
Chris Wright<chrisw@xxxxxxxxxxxx>
Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function
Date: Tue, 04 Jan 2011 19:05:54 +0100
RT guests don't make sense, there's nowhere near enough infrastructure
for that to work well.

I'd argue that KVM running with RT priority is a bug.
Peter, can I ask why did you state that ? In the IRMOS project, we
are just deploying KVM VMs by using the Fabio's real-time scheduler
(for others, a.k.a., the Fabio's EDF throttling patch, or IRMOS RT scheduler)
in order to let the VMs get precise CPU scheduling guarantees by the
kernel. So, in this context we do have KVM running at RT priority, and
we do have experimental results showing how this can improve stability
of performance of the hosted guest VMs.
Of course, don't misunderstand me: this is a necessary condition for a
stable performance of KVM VMs, I'm not saying it is sufficient for

Tommaso Cucinotta, Computer Engineering PhD, Researcher
ReTiS Lab, Scuola Superiore Sant'Anna, Pisa, Italy
Tel +39 050 882 024, Fax +39 050 882 003

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