Poor 8139 network card performance when sharing IRQ

[Ricardo Ferreira <stormlabs@gmx.net>]

I have a dual p3-1Ghz on a Abit VP6 board. Everything is working well except 
the network card. I have some nfs mounts and i'm using 4096 wsize and rsize 
for performance. However when eth0 and any other card are sharing an IRQ the 
result of a ping to the server with a packetsize of 4096 is this:

$ ping -s 4096 fs
PING loki.internal (192.168.0.40): 4096 data bytes
4104 bytes from 192.168.0.40: icmp_seq=0 ttl=255 time=1.6 ms
4104 bytes from 192.168.0.40: icmp_seq=1 ttl=255 time=283.5 ms
4104 bytes from 192.168.0.40: icmp_seq=2 ttl=255 time=755.3 ms
4104 bytes from 192.168.0.40: icmp_seq=3 ttl=255 time=2.1 ms
4104 bytes from 192.168.0.40: icmp_seq=4 ttl=255 time=1.6 ms
4104 bytes from 192.168.0.40: icmp_seq=5 ttl=255 time=2.1 ms
4104 bytes from 192.168.0.40: icmp_seq=6 ttl=255 time=1.8 ms
4104 bytes from 192.168.0.40: icmp_seq=7 ttl=255 time=284.1 ms
4104 bytes from 192.168.0.40: icmp_seq=8 ttl=255 time=2.0 ms
4104 bytes from 192.168.0.40: icmp_seq=9 ttl=255 time=284.4 ms
4104 bytes from 192.168.0.40: icmp_seq=10 ttl=255 time=2.0 ms
4104 bytes from 192.168.0.40: icmp_seq=11 ttl=255 time=2.2 ms
4104 bytes from 192.168.0.40: icmp_seq=12 ttl=255 time=754.9 ms
4104 bytes from 192.168.0.40: icmp_seq=13 ttl=255 time=283.7 ms
4104 bytes from 192.168.0.40: icmp_seq=14 ttl=255 time=391.9 ms
 
--- loki.internal ping statistics ---
15 packets transmitted, 15 packets received, 0% packet loss
round-trip min/avg/max = 1.6/203.5/755.3 ms

... but if i remove the other card (in this case a Miro Video TV Card) the 
ping times all drop to about 2ms. 

Is this drop in performance normal or is it a bug ? As an aside, anything 
lower than 1024 packetsize doesn't slowdown.

Thanks
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