Date: Mon, 31 Oct 2005 08:37:09 +0800 From: David Xu <davidxu@freebsd.org> To: "M. Warner Losh" <imp@bsdimp.com> 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?) Message-ID: <43656735.7080505@freebsd.org> In-Reply-To: <20051030.161606.65680605.imp@bsdimp.com> References: <20051030093718.GE39253@dragon.NUXI.org> <4364D90F.3090205@samsco.org> <20051030195936.GZ4115@funkthat.com> <20051030.161606.65680605.imp@bsdimp.com>
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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
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