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Date: Sat, 2 Jun 2007 17:31:46 -0400
From: Kris Kennaway <kris@obsecurity.org>
To: Poul-Henning Kamp <phk@phk.freebsd.dk>
Message-ID: <20070602213146.GA1302@rot13.obsecurity.org>
References: <20070602194151.GA1604@rot13.obsecurity.org>
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Cc: takawata@freeBSD.org, Dag-Erling Sm??rgrav <des@des.no>,
	Nate Lawson <nate@root.org>, current@freeBSD.org,
	Kris Kennaway <kris@obsecurity.org>
Subject: Re: HPET vs other timers
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On Sat, Jun 02, 2007 at 09:15:13PM +0000, Poul-Henning Kamp wrote:
> In message <20070602194151.GA1604@rot13.obsecurity.org>, Kris Kennaway writes:
^^^
JFYI, I didn't :-)

> 
> >> 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.
>