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

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Message-ID: <20091029130309.GA2750@think>
Date:	Thu, 29 Oct 2009 09:03:09 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Glauber Costa <glommer@...hat.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	kurt.hackel@...cle.com, the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Keir Fraser <keir.fraser@...citrix.com>, zach.brown@...cle.com,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall
 implementation

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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