3c905C: very high system/interrupt CPU usage

Peter Schuller peter.schuller at infidyne.com
Sat Oct 15 08:30:50 PDT 2005


I have a machine here with a couple of 3c905C:s in it. For some
reason, network activity causes very high amounts of system and
interrupt CPU usage. By "very high" i mean more than 50% interrupt,
and more than 25% system usage.

It is not just a measuring issue either, because the whole reason I
looked into it was that file transfers have been slow for as long as I
can remember.  Especially with ssh, everything is extremely slow given
that only a small fraction of the available CPU resources are left
over for userspace.

Any ideas on what would cause this? I am not experiencing any other
issues with the NIC or anything else, its just the high CPU
usage. Could it be that the xl driver has fallen back to not using DMA
(is that even supported with 3c905c?)? If this is the case, is there a
way to find out whether it is currently using DMA? (I see nothing in
particular in the kernel log).

Also: The CPU usage problem occurrs on both outgoing and incoming
traffic, and on both NIC:s.

/ Peter Schuller, InfiDyne Technologies HB

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