GigE Performance Comparison of GMAC and SUNGEM Drivers

David S. Miller davem at
Wed Nov 21 11:19:37 EST 2001

   From: benh at
   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.

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