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RE: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation

To: Avi Kivity <avi@xxxxxxxxxx>
Subject: RE: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Wed, 7 Oct 2009 15:36:58 -0700 (PDT)
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, kurt.hackel@xxxxxxxxxx, the arch/x86 maintainers <x86@xxxxxxxxxx>, Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Linux, zach.brown@xxxxxxxxxx, chris.mason@xxxxxxxxxx
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> Then they will get incorrect timing once they are live migrated.

I've posted a proposed (OS-independent) solution for that and
am (slowly) in the process of implementing it.

> -----Original Message-----
> From: Avi Kivity [mailto:avi@xxxxxxxxxx]
> Sent: Wednesday, October 07, 2009 3:08 PM
> To: Dan Magenheimer
> Cc: Jeremy Fitzhardinge; Jeremy Fitzhardinge; Xen-devel; Kurt Hackel;
> the arch/x86 maintainers; Linux Kernel Mailing List; Glauber 
> de Oliveira
> Costa; Keir Fraser; Zach Brown; Chris Mason
> Subject: Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall
> implementation
> 
> 
> On 10/07/2009 10:48 PM, Dan Magenheimer wrote:
> >> We can support them by falling back to the kernel.  I'm a 
> bit worried
> >> about the kernel playing with the hypervisor's version field.  It's
> >> better to introduce yet a new version for the kernel, and 
> check both.
> >>      
> > On Nehalem, apps that need timestamp information at a high
> > frequency will likely use rdtsc/rdtscp directly.
> >
> >    
> 
> Then they will get incorrect timing once they are live migrated.
> 
> -- 
> I have a truly marvellous patch that fixes the bug which this
> signature is too narrow to contain.
> 
> 
>

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