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To: Kris Kennaway <kris@obsecurity.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Sat, 02 Jun 2007 15:41:51 -0400."
	<20070602194151.GA1604@rot13.obsecurity.org> 
Date: Sat, 02 Jun 2007 21:15:13 +0000
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Cc: takawata@freeBSD.org, Dag-Erling Sm??rgrav <des@des.no>,
	current@freeBSD.org, Nate Lawson <nate@root.org>
Subject: Re: HPET vs other timers 
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In message <20070602194151.GA1604@rot13.obsecurity.org>, Kris Kennaway writes:

>> Anyone able to speculate why though?  HPET only reads 32 bits from a
>> memory mapped region.  No locking or other requirements.  ACPI_timer
>> does multiple IO ops, which according to bde@ are much slower than
>> memory reads.  

HPET needs to do metastability mitigation and is not "just a read
from a memory mapped region".

-- 
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.