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Date: Tue, 15 Apr 2008 16:41:22 +0900
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From: gnn@freebsd.org
To: Andrew Gallatin <gallatin@cs.duke.edu>
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Cc: current@freebsd.org
Subject: Re: TSC Timecounter and multi-core/SMP
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At Fri, 11 Apr 2008 08:34:29 -0400 (EDT),
Andrew Gallatin wrote:
> 
> 
> gnn@freebsd.org writes:
>  > Howdy,
>  > 
>  > Is the TSC timecounter synchronized across multiple cores and/or
>  > processors?  A quick search seems to indicate it's not but I'd like to
>  > find a definitive reference on the TSC.
> 
> There is a great comment in the OpenSolaris source code talking about
> TSCs and their behavior on SMP systems.  See
> http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/i86pc/os/timestamp.c
> 

Actually this was a very helpful bit of reading.

I also believe that at least per processor there is only 1 TSC, that
is, on a 2 or 4 core, all cores share the same TSC.

Best,
George