GigE Performance Comparison of GMAC and SUNGEM Drivers

[David S. Miller]

   From: benh at kernel.crashing.org
   Date: Wed, 21 Nov 2001 01:05:18 +0100

   Ah, ok, I stand corrected. Is this a bug in the chip or a flaw of
   the GEM chip design ? I mean, is there a chance that later revs
   of the chip or eventually the one used by Apple can support it ?

There is no chance whatsoever of this ever working on any
GEM revision.

Even if it could work, GEM has a 9K transmit and 20K receive fifo in
the largest configuration.  Even the Acenic has 512k or 1MB of total
on-chip ram for packet buffering.

As a result GEM sends pause frames when there is even the slightest
amount of DMA traffic is has to compete with.  On a 33Mhz/32-bit PCI
bus, it is sending pause frames all the time even if it is the only
agent making use of the bus.

** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/