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Date: Sun, 20 Apr 2008 22:12:31 -0700
From: Julian Elischer <julian@elischer.org>
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To: Daniel O'Connor <doconnor@gsoft.com.au>
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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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Daniel O'Connor wrote:
> On Fri, 18 Apr 2008, Julian Elischer wrote:
>> 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.
> 
> Probably because it's very very difficult to get right :)	

and they've had over 20 years to think of something.

>