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To: Julian Elischer <julian@elischer.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 17 Apr 2008 19:07:50 MST."
	<48080276.3040203@elischer.org> 
Date: Fri, 18 Apr 2008 06:00:08 +0000
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Cc: gnn@freebsd.org, freebsd-current@freebsd.org,
	Andrew Gallatin <gallatin@cs.duke.edu>
Subject: Re: TSC Timecounter and multi-core/SMP 
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In message <48080276.3040203@elischer.org>, Julian Elischer writes:
>David O'Brien wrote:
>
>> 
>> The TSC on K8 is not invariant - its rate of change is affected by
>> P-state changes.
>> 
>> The TSC on Greyhound (Family 10h) is invariant.
>> [but as stated above, is not synced with other cores]
>
>You'd think that an invariant sync'd clock (fast to read) of some
>type would have been done by someone by now.. The software people
>have been asking for this for the last decade at least.

Actually one of the original design documents for SAGE stressed that
such hardware were crucially important "for any system operating
in real time", so yes, the HW people have had adequate notices.

Poul-Henning


-- 
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.