From owner-freebsd-net@FreeBSD.ORG  Fri Oct 14 08:46:56 2005
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To: Andrew Gallatin <gallatin@cs.duke.edu>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 13 Oct 2005 19:54:55 EDT."
	<17230.62415.991707.840932@grasshopper.cs.duke.edu> 
Date: Fri, 14 Oct 2005 10:46:53 +0200
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Cc: Garrett Wollman <wollman@csail.mit.edu>, net@FreeBSD.ORG
Subject: Re: Call for performance evaluation: net.isr.direct (fwd) 
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In message <17230.62415.991707.840932@grasshopper.cs.duke.edu>, Andrew Gallatin
 writes:

>Linux already takes care of syncing the TSC between SMP cpus, so we
>know it is possible.  This seems like a much more doable optimization.
>And it is likely to have other benefits..

Validating that the TSC is reliable is a nontrivial task which requires
access to a lot of NDA information and an extensive positive/negative
list of chips and chipsets.

Even in the most recent chips, there are still issues with TSC that
makes it unusable as a default timecounter.

-- 
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.