[eepro100] Packets per Interrupt ..

Henner Zeller zeller@stud.fh-heilbronn.de
Mon, 2 Oct 2000 00:20:01 +0200 (CEST)

I recently got the chance to test a Harware traffic generator which can
generate Ethernet frames at arbitrary rates and sizes. I ran a test with
the smallest possible Ethernet frame (64Byte) at 100% 100MBit rate - and
the linux machine attached to the other end (Kernel 2.2.17, eepro100 
as module) seemed to receive most of the packets (what ifconfig reports),
but is completely locked during the traffic generation with obviously
100% system load.

The reason for this seems to be the number of interrupts generated: In
this case, the EthernetPro generates one interrupt per two packets
(compare /proc/interrupts before, after) which translates into > 70000
Interrupts per second (sending packets as described above means about
148000 frames per second).
Surly noting a PC-architecture can handle easily (not even with Linux ;-).

Playing around with some module parameters does not seem to influence the
number of interrupts generated (congenb ?). Is there any way in the
eepro100 driver to do this currently (it must be possible somehow, since
on legacy 'opeating systems' (NT ..) this does not seem to harm the
system performance .. cough, cough).

I want to use the Ethernet Pro NIC in a heavily loaded network as sniffing
device, but this seems to eat up valuable CPU resources..