TSC Timecounter and multi-core/SMP

[Jeff Roberson]

On Tue, 15 Apr 2008, gnn at freebsd.org wrote:

> At Fri, 11 Apr 2008 08:34:29 -0400 (EDT),
> Andrew Gallatin wrote:
>>
>>
>> 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
>>
>
> 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.

I think we should confirm whether this is the case with earlier opterson. 
I have seen two processors on the same die out of sync.

Jeff

>
> Best,
> George
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