Performance problem on i810e-based motherboard

[Peter Monta <pmonta@terayon.com>]

I'm seeing puzzlingly low PCI performance from an i810e-based
motherboard.  Could something be mistuned, similar to the 'PCI
streaming bit' I saw mentioned in the archives about much older
chipsets?

With nothing active on PCI except a gigabit-Ethernet
card (Netgear GA620), UDP jumboframe transmits go at around
50 MBytes/sec compared to the 440BX result of around 91 MBytes/sec.

Unfortunately I don't have a PCI bus analyzer to watch the burst
patterns.  As far as I can see from the NIC manual, the board does MRM
reads.  The throttling mentioned in the GMCH data sheet (register
MISCC) is not set.  I didn't see anything in the ICH data sheet that
looked relevant.  (Incidentally, a dump of the GMCH configuration
registers shows nonzero stuff at locations 0x81 and 0x82, just after
MISCC, that the data sheet lists as "reserved".  Could this be
relevant configuration?)

Is there any Intel documentation about expected performance
for streaming PCI reads or writes using the i810e?  I suppose
it's possible that PCI isn't the issue at all, and that for
some reason the hub interface is the bottleneck.

Cheers,
Peter Monta   pmonta@terayon.com
Terayon Communications Systems