I finally got various NICs working on my Redhat Linux test machine (dual-booting Redhat 8 with kernel 2.4.18-14 and Redhat 7.3 with kernel 2.4.18-3), but I'm seeing capture performance much lower than I expect.
Using a gigabit packet generator, I've been generating various loads for the box. I'm finding, however, that even at relatively low rates (7MB/s), and for short times (send 150MB total), Ethereal/tethereal either doesn't capture, or isn't passed 30% of the packets I send. At higher rates (but still low), Ethereal only manages to capture 40% of the packets on the wire. The adapter is seeing the packets, as netstat -i counters are increasing by the exact number of frames that I send.
Let me describe my setup. The capture device is running dual Athlon XP 1800+ processors, 512MB DDR RAM, SysKonnect SK-9844 or SK-9843 64-bit, 66mhz GigEth NICs. I'm generating 1000byte frames only. I'm performing no frame slicing, and have been capturing either with tethereal (and writing directly to a disk file), or with Ethereal (and capturing to RAM). I've tested a wide variety of settings, from high data rates (45MB/s), low (7MB/s), "bursty", long tests (20 minutes and quite a few gigabytes of data), and short ones (as low as 100MB of data sent).
CPU doesn't seem to be sweating at all during most of my tests (20% used or below), and at no disk paging is occurring. I've also tried turning SMP off, but I saw no noticable difference.
Tethereal is reporting only seeing a certain number of frames (again, 30-70% or so), and reports 0 dropped. I'm not 100% sure whether the kernel is compiled to allow drop reporting, so I'm not sure what this symptom is telling me.
Any suggestions on what might be happening here? I get MUCH better rates in Windows with the exact same system configuration. I'm going to try eliminating the cards/driver by using a NetGear GA620, and check TCPDump to see if I get similar results, but otherwise I'm open to suggestions on what to check/try...
Thanks, Ian
