linux-kernel - Re: [RFC -v3 PATCH 0/3] directed yield for Pause Loop Exiting

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Message-ID: <1294137134.4379.9.camel@marge.simson.net>
Date:	Tue, 04 Jan 2011 11:32:14 +0100
From:	Mike Galbraith <efault@....de>
To:	Avi Kivity <avi@...hat.com>
Cc:	Rik van Riel <riel@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [RFC -v3 PATCH 0/3] directed yield for Pause Loop Exiting

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


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