Processor contention(?) and network bandwidth on AMD
jlb17 at duke.edu
Mon Apr 29 12:05:47 EDT 2002
This is probably in the category of "Yup, that's the way it is, deal with
it", but, just in case anyone has any ideas, I'm throwing it out there.
In the course of testing the gigabit connection in a new server, I noticed
that overloaded dual AMD systems take a big hit in network bandwidth. I'm
testing with ttcp, and all connections were made over the same switch (HP
As an example, the results for a Tiger MPX (S2466) based node with dual
1900+s and using the integrated 3Com are:
unloaded: 11486.6 KB/real sec
2 matlab simulations: 10637.8 KB/real sec
2 matlab simulations and 2 SETI at homes (nice -19): 6645.4 KB/real sec
Ouch. This is on RedHat 7.2 with kernel 2.4.9-31.
I eliminated every variable I could think of -- I tried this on an S2462
(Thunder MP) based system, I used a PCI Intel eepro100 card rather than
the built-in 3Com, I upgraded to an almost vanilla (French Vanilla?)
2.4.18 kernel (the one from SGI's 1.1 XFS release). All showed the same
results (well, 2.4.18 didn't show much of a drop with just the two
matlabs, but still crashed with matlab+SETI). The one Intel system I
tested (dual PIII 933 on an i860) showed very little bandwidth drop with
load, and no extra drop for an overload.
Any ideas? Is there any way to fix this? Or is the answer just to not
run background nice jobs on cluster nodes?
Department of Biomedical Engineering
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