Re: (Re:) RDTSC-based Fortran-callable timer for Opteron/Linux

From: glen herrmannsfeldt (gah_at_ugcs.caltech.edu)
Date: 01/07/05 

Date: Fri, 07 Jan 2005 10:06:55 -0800

Greg Lindahl wrote:

(snip)

> 4 billion / 2 Ghz = 2 seconds.

> So it's not just theoretical, it rolls over ~ every 2 seconds.

> BTW this instruction is not SMP-safe: different cpus have different
> counters.

As I understand it, they are supposed to be synchronized, but
then how many people would notice, and report the bug, if
they weren't?

You can't really compare results between different threads, and
you will likely see a large count increase on a context switch.

-- glen

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