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Date: Mon, 31 Oct 2005 08:37:09 +0800
From: David Xu <davidxu@freebsd.org>
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To: "M. Warner Losh" <imp@bsdimp.com>
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Cc: Alexander@Leidinger.net, gurney_j@resnet.uoregon.edu,
	freebsd-current@FreeBSD.org
Subject: Re: TSC instead of ACPI: powerd doesn't work anymore (to be
	expected?)
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M. Warner Losh wrote:

>Actually, ioport reads can be faster than the 1us that's widely
>quoted.  ioport reads can be as fast as ~125ns (2 cycles at 16MHz).
>However, experience has shown that they are rarely this fast.  I've
>seen 8MB/s pio over the pci bus on some custom hardware we have, which
>2Mreads/sec which is about 500ns per read.  I think that the pci
>hardware that I was reading had a few extra wait states...
>
>The 1us/read is for devices on the ISA bus or for hardware that
>emulates this timing.
>
>Warner
>
>
>  
>
The ioport speed is also unstable, on my IBM T43 thinkpad notebook,
if I load wireless driver, the gettimeofday syscall will be 4 times slower
than no wireless driver loaded, though I am not using the wireless
network.

David Xu