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

To:	Avi Kivity <avi@xxxxxxxxxx>
Subject:	Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation
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>
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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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Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation