Date: Mon, 22 Mar 1999 10:16:27 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: Mike Smith <mike@smith.net.au> Cc: Amancio Hasty <hasty@rah.star-gate.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Gigabit ethernet -- what am I doing wrong? Message-ID: <14070.22663.501605.138166@grasshopper.cs.duke.edu> In-Reply-To: <199903212129.NAA00925@dingo.cdrom.com> References: <199903212013.MAA50370@rah.star-gate.com> <199903212129.NAA00925@dingo.cdrom.com>
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Mike Smith writes:
> >
> > Hmm....
> > Does anyone know when the faster PCI busses (64bits or 66MHz PCI clock rate)
> > are going to be availabe ?
>
> 64-bit PCI has been available on Alpha and Sparc systems for some time.
Be very, very wary of 64-bit PCI implementations on Alphas and
UltraSparcs. In many cases a 32-bit intel 440BX or similar chipset
will outperform 64-bit Alpha or Sun chipsets.
On alphas, the only workstation 64-bit PCI implentation which is free
from performance problems with is the new Tsunami chipset, used in the
new 21264 workstations & small servers (XP1000, DS20, DP264) (older
server chipsets might be OK, but I don't know -- we don't have any
4100's or 8x00s). Machines based on the Pyxis (21174) chipset have
great DMA write bandwidth, but bad DMA read bandwidth and early
revisions are buggy as well. On the miata (Personal Workstation) this
can be 'fixed' by removing the L3 cache. On the AlphaPC164lx, this
can be 'fixed' by turning on DMA read prefetching in the PXYS_CTRL
register -- which works great for Myrinet Lanai5 cards, but will lock
a machine with an older Myrinet Lanai4, or Alteon card. The older CIA
(2117{1,2}) chipset (used in AlphaStations and EB164's) has great DMA
read bandwidth, but terrible DMA write bandwidth.
Suns have similar performance problems. They do have the advantage of
being able to run 64-bit cards a 66Mhz, which makes up for a lot if
your NIC supports it (Alteon does).
Take a look at http://www.myri.com:80/scs/PCI64X/performance for
64-bit, 33Mhz DMA performance numbers. And
http://www.myri.com:80/myrinet/performance/DMAperf.html for 32-bit,
33Mhz numbers. They call DMA reads 'E2L', and DMA writes 'L2E'.
Drew
------------------------------------------------------------------------------
Andrew Gallatin, Sr Systems Programmer http://www.cs.duke.edu/~gallatin
Duke University Email: gallatin@cs.duke.edu
Department of Computer Science Phone: (919) 660-6590
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