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Subject: Re: [RFC -v3 PATCH 0/3] directed yield for Pause Loop Exiting
From: Mike Galbraith <efault@gmx.de>
To: Avi Kivity <avi@redhat.com>
Cc: Rik van Riel <riel@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Chris Wright <chrisw@sous-sol.org>
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Date: Tue, 04 Jan 2011 11:32:14 +0100
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On Tue, 2011-01-04 at 11:09 +0200, Avi Kivity wrote:
> On 01/04/2011 08:42 AM, Mike Galbraith wrote:

> > If I were to, say, run a 256 CPU VM on my quad, would this help me get
> > more hackbench or whatever oomph from my (256X80386/20:) box?
> 
> First of all, you can't run 256 guests on x86 kvm.

I didn't want 256 guests. Just one great big dog slow virtual playpen :)

> > >  Both Intel and AMD CPUs have a feature that detects when a virtual
> > >  CPU is spinning on a lock and will trap to the host.
> >
> > Does an Intel Q6600 have this trap gizmo (iow will this do anything at
> > all for my little box if I were to try it out).
> 
> Likely not.  Run 
> http://git.kernel.org/?p=virt/kvm/qemu-kvm.git;a=blob_plain;f=kvm/scripts/vmxcap;hb=HEAD, 
> look for 'PAUSE-loop exiting'.  I think the first processors to include 
> them were the Nehalem-EXs, and Westmeres have them as well.

Oh darn, need new box to get all the toys.  Thanks.

	-Mike