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From: Robert Watson <rwatson@FreeBSD.org>
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Cc: freebsd-current@freebsd.org
Subject: Re: dtrace users opinion solicited (timestamps)
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On Fri, 10 Jul 2009, Andriy Gapon wrote:

> Thinking aloud - maybe we could always use one value of tsc_freq (or 
> something like max_tsc_freq). This wouldn't give us correct timestamps when 
> TSC frequency is changing, but it would give us something that is always 
> proportional to TSC value and thus has its properties - monotonicity in the 
> first place. And, of course, there is no problem when TSC frequency is 
> constant.

Just a point from a user perspective: I find it useful (important even) to be 
able to compare timing between runs on the same box, and while that means I 
need to control for the frequency changing in an experimental sense, in as 
much as timestamp measurements in dtrace can be normalized, that would be 
helpful.

Robert N M Watson
Computer Laboratory
University of Cambridge