Re: [Myricom help #16903] Myrinet on Tyan-2720 motherboard

David,

On Monday 13 January 2003 09:44 am, David B. Ritch wrote:
> Has anyone successfully used Myrinet with Tyan 2720 motherboards?  If
> so, was there anything unusual you did to get it to work?  Which PCI
> slots were the Myrinet boards in?
>
> We're having trouble with Myrinet on a small cluster based on Tyan
> 2720's.  I've seen Myrinet cards show an extreme sensitivity to which
> PCI slot they are in (another cluster gave consistently incorrect
> results for HPL, until we moved the Myrinet cards to a different but
> supposedly equivalent slot), and I've seen some BIOS issues on this
> motherboard.  Both lead me to suspect that the Myrinet problems we're
> observing may have as much to do with the motherboard as the Myrinet.

We have seen various problems with these motherboards: different
timings on the PCI depending upon the PCI slot, low quality Tyan
riser cards, bad APIC support (either the hardware or the Linux
kernel support) requiring the customer to disable APIC to avoid
interrupt problems (details in the Caveats section of the 
README-linux).

We have the following "Caution" in our documentation -- "Guide
to Myrinet PCI/Host Interfaces", and the "Myrinet Installation
and Troubleshooting Guide".
  http://www.myri.com/scs/#documentation

Caution: Riser cards can be a significant source of problems in a 
hardware configuration. Although PCI riser cards are commonly used,
they will generally violate PCI specifications for the length of 
signal traces. A riser card may also introduce impedance 
discontinuities and signal degradation between the mother board,
riser card, and interface card. If you observe PCI-communication 
errors when using a riser card, refer to the diagnostic procedure 
below. A higher quality riser card one whose traces match the 
impedance of signals on the mother board and interface may also 
solve the problem.

It is important that a 64-bit riser card is used in a 64-bit PCI slot,
and likewise a 32-bit riser card is used in a 32-bit PCI slot. If you
are using a riser card with multiple slots, the Myrinet interface 
should be placed in the slot closest to the PCI connector on the 
mother board to minimize the distance between the PCI connector on 
the mother board and the PCI connector on the riser card. Otherwise,
the Myrinet PCI interface may not be correctly detected and/or
serious performance irregularities will result.

Hope this helps.
Susan

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Susan Blackford
Member of Technical Staff
Myricom Inc.
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