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Date: Fri, 10 Jul 2009 08:50:47 +0300
From: Andriy Gapon <avg@freebsd.org>
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To: Tim Kientzle <kientzle@freebsd.org>
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Cc: =?ISO-8859-1?Q?Marius_N=FCnnerich?= <marius@nuenneri.ch>,
	freebsd-current@freebsd.org
Subject: Re: dtrace users opinion solicited (timestamps)
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on 10/07/2009 05:54 Tim Kientzle said the following:
> 
> Instead of just storing tsc_freq at each frequency change,
> you really need:
>   * Last timestamp just before frequency change (t0)
>   * new frequency (f)
>   * TSC value at frequency change (c0)
> 
> Then
>    t = t0 + (rdtsc() - c0) / f
> 
> Of course, I haven't looked at the code to tell
> what your range limitations are.

Yes, tracking the TSC frequency changes should allow us to have correct DTrace
timecounting. But I am not sure if we really need this (or can have this).
Because otherwise I can not see why we have a distinct/specialized DTrace
TSC-based timecounting when we already have general purpose TSC timecounting
that already works correctly (if I am not mistaken).

-- 
Andriy Gapon