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

from [Jeremy Fitzhardinge] [Permanent Link][Original]
To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 27 Oct 2009 11:20:10 -0700
Cc: 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>, Avi Kivity <avi@xxxxxxxxxx>, zach.brown@xxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, chris.mason@xxxxxxxxxx, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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On 10/27/09 10:29, Dan Magenheimer wrote:
> Is there any way for an application to conclusively determine
> programmatically if the "fast vsyscall" pvclock is functional
> vs the much much slower gettimeofday/clock_gettime equivalents?
>
> If not, might it be possible to implement some (sysfs?)
> way to determine this, that would also be backwards compatible
> to existing OS's that don't have pvclock+vsyscall supported?
>   

It would probably be simplest and most portable for the app to just
measure the performance of gettimeofday and see if it meets its needs.

    J

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