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

Mike Galbraith
2011-01-04T10:32:14Z

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