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From: David Mosberger <davidm@napali.hpl.hp.com>
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Date: Tue, 14 Jan 2003 13:34:15 -0800
To: "Howell, David P" <david.p.howell@intel.com>
Cc: "Maciej Soltysiak" <solt@dns.toxicfilms.tv>,
       <linux-kernel@vger.kernel.org>
Subject: RE: timing an application
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>>>>> On Tue, 14 Jan 2003 12:37:05 -0800, "Howell, David P" <david.p.howell@intel.com> said:

  Dave> If this is on a IA32(Pentium II or later)/IA64 have you
  Dave> considered using the processor TSC register to get interval
  Dave> timestamps? It's a lot lighter weight and should give better
  Dave> resolution. When we have done this we compared the tick values
  Dave> directly.

  Dave> To convert TSC ticks to time the /proc/cpuinfo value for 'cpu
  Dave> MHz', see the glibc get_clockfreq.c and hp_timing.h
  Dave> implementation for details.

Note that it's tricky to uses TSC/ITC on multiprocessors, especially
on large machines, on which the clocks for different CPUs may drift, etc.
It's much better to use the clock_gettime() routine:

  http://www.opengroup.org/onlinepubs/007908799/xsh/clock_getres.html

Where properly implemented, this will be both as fast and accurate.

	--david
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