TSC Timecounter and multi-core/SMP

[Andrew Gallatin]

gnn at 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