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Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation
- To: Avi Kivity <avi@xxxxxxxxxx>
- From: Chris Mason <chris.mason@xxxxxxxxxx>
- Date: Thu, 29 Oct 2009 09:03:09 -0400
- Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, kurt.hackel@xxxxxxxxxx, Glauber Costa <glommer@xxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, zach.brown@xxxxxxxxxx, Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>
- Delivery-date: Thu, 29 Oct 2009 06:04:10 -0700
- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
- Mail-followup-to: Chris Mason <chris.mason@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Glauber Costa <glommer@xxxxxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, kurt.hackel@xxxxxxxxxx, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, zach.brown@xxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>
On Thu, Oct 29, 2009 at 02:13:50PM +0200, Avi Kivity wrote:
> On 10/28/2009 07:47 PM, Jeremy Fitzhardinge wrote:
> >>Much better to have an API for this. Life is hacky enough already.
> >My point is that if an app cares about property X then it should just
> >measure property X. The fact that gettimeofday is a vsyscall is just an
> >implementation detail that apps don't really care about. What they care
> >about is whether gettimeofday is fast or not.
>
> But we can not make a reliable measurement.
I can't imagine how we'd decide what fast is? Please don't make the
applications guess.
-chris
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