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Date: Fri, 11 Apr 2008 08:34:29 -0400 (EDT)
To: gnn@freebsd.org
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Cc: current@freebsd.org
Subject: Re: TSC Timecounter and multi-core/SMP
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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

FWIW, solaris manages to keep track of unsynchronized TSCs, and use
unsynchronized TSC timecounters for timekeeping on SMP systems.  It
would be nice if FreeBSD could do the same.

Drew