Intel i860 has same bug as i850?
From JC's site:
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A most excellent fellow, Duraid Madina, tells me of most non-excellent news. Apparently, the PCI-oriented bug which plagued the i850 chipset is also present in the i860 chipset. If you recall, Intel initially delayed the Pentium 4 introduction because of this erratum, but eventually decided that it was not critical enough to care about. But the same problem could conceivably be more critical for workstations and/or servers. Let's see what this fellow said:
"the i860 chipset suffers from _exactly the same bug_ as the i850 chipset (I think it's the fact that it's the _same_ bug that makes it interesting) and it is this: Neither the 860 nor the 850 chipsets can sustain more than 90MB/sec transfer _to_ a PCI bus. This is not the same as _from_ the PCI bus.
However, this is quite odd, especially considering that every i860 motherboard available features 64-bit PCI. It is true to say that no matter what sort of P4/P4Xeon system you buy, you could _not_ saturate a single gigabit ethernet card, if you were sending (e.g. running a huge FTP server or something).
Far more disappointingly, people will not be able to use P4/P4Xeon systems effectively with Myrinet cards (www.myri.com) to build high performance beowulf clusters. It seems inevitable that i840 or 760MP boards will outperform them as soon as I/O becomes significant (but I wouldn't even say 'I/O-bound')
The 90mb/sec PCI limit only applies in the case where a PCI card is mastering the bus and going 'hey, I want to read <XYZ> from RAM' where <XYZ> is bigger than 8 bytes. So yeah, if a card is trying to transfer huge amounts of data straight from system memory to itself, it'll bump into this limit.
I don't _think_ this bug exists with the AGP port. I'm not sure, but it just doesn't look that way...".
That there's something to chew on. Can we get any corroborating word or some decent dismissals on this one?
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Amusing, if true.
Doug
p.s. Don't shoot the messenger. :) Thoughts? |
