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Date: Mon, 14 Dec 2009 22:08:38 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] cpuid problem in upstream qemu with kvm
Message-ID: <20091214200838.GB27769@redhat.com>
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: avi@redhat.com, qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>

On Mon, Dec 14, 2009 at 02:02:03PM -0600, Anthony Liguori wrote:
> Gleb Natapov wrote:
> >>I thought KVM emulates the syscall instruction?  I swear I've seen
> >>patches for that.
> >>
> >It is. Starting from 2.6.32.
> 
> Okay, so this is a performance vs. migration compatibility issue then?
> 
> BTW, couldn't we just not advertise syscall in cpuid?  That should
> fix it too without sacrificing migration compatibility.  We get a
> slight slowdown on AMD hosts but that's probably minor compared to
> the cost of using emulated syscall on Intel hosts.
> 
As far as I understand not advertising syscall for 64bit CPU is not a
valid option.

--
			Gleb.