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To: Maxim Sobolev <sobomax@FreeBSD.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 10 Apr 2008 13:52:28 MST."
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Date: Thu, 10 Apr 2008 21:45:41 +0000
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Sender: phk@critter.freebsd.dk
Cc: gnn@FreeBSD.org, Kris Kennaway <kris@FreeBSD.org>, current@FreeBSD.org
Subject: Re: TSC Timecounter and multi-core/SMP 
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In message <47FE7E0C.4070801@FreeBSD.org>, Maxim Sobolev writes:
>Kris Kennaway wrote:
>> gnn@freebsd.org wrote:
>>> 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.
>> 
>> Modern Intel systems tend to be synchronized, in my experience.
>
>I really doubt they are. As far as I know newest milti-core chips can 
>modulate frequency of even suspend individual cores independently of 
>each other, which would make such synchronization difficult to maintain 
>if the power management is on.

P4 (and I think most newer chips) have a TSC that runs independent
of the cpu clock frequency, and supposedly, always at constant rate.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.