[Beowulf] gigabit ethernet: horrible performance for 0 byte messages
bwegner at ekt.tu-darmstadt.de
Wed Feb 11 05:02:23 EST 2004
I have a really small "cluster" of 4 PC's which are connected by a normal
Ethernet 100 Mbit switch. Because the motherboards have Gigabit-LAN on board
I thought I might be able to improve performance by connecting the machines
via a Gigabit switch (which are really cheap nowadays).
Everything seemed to work fine. The switch indicates 1000Mbit connections to
the PC's and transfer rate for scp-ing large files is significantly higher
now, but my software unsing mpich RUNS about a factor of 4-5 SLOWER NOW than
with the 100 Mbit switch.
I wasn't able to actually track down the problem, but it seems that there is
a problem with small messages. When I run the performance test provided with
mpich, it reports (bshort2/bshort4) extremely long times (e.g. 1500 us) for 0
byte message length, while for larger messages everything looks fine (linear
dependancy of transfer time on message length, everything below 300 us). I
have also tried mpich2 which shows exactly the same behavior.
Does anyone have any idea?
Here are the details of my system:
- Suse Linux 9.0 (kernel 2.4.21)
- motherboard ASUS P4P800
- LAN (10/100/1000) on board (3COM 3C940 chipset)
- LevelOne 10/100/1000 8-port Fast Ethernet Switch (chipset: TC9208M +
Mit besten Grüßen -- Best regards,
Dipl.-Ing. Bernhard Wegner
Fachgebiet Energie- und Kraftwerkstechnik
Technische Universität Darmstadt
Petersenstr. 30 64287 Darmstadt Germany
phone: +49-6151-162357 fax: +49-6151-166555
e-mail: bwegner at ekt.tu-darmstadt.de
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