Re: Trouble with 3c905 new cards (CX-TX)

On Wed, 9 Jul 2003, Simone Montagnani wrote:

> I have a Linux redhat 7.3 Cluster (40 Biproc-nodes) with 3com 3C905CX-TX, I 
> have network performance problems

Running the application was the only diagnostic that you have run ? You 
could try ttcp or netperf to see what the network is capable of, without 
any additional CPU or disk load.

> When I run my application this 10 computers go really faster (I mean for
> network wall time are equal to 40 nodes! ).

But this is not a reason to suspect the network: parallel applications 
follow Amdahl's law and they don't scale linearly. Usually at some point 
the time taken to run on N CPUs is equal or even smaller than the time 
taken to run on 2*N CPUs; it means that you have hit the maximum number of 
CPUs that can be used for running this application in parallel (this is a 
very rough explanation, look up any parallel computing theory book for 
more details).

> is this a driver problem?or a chipset card problem?

I don't exclude the network card/driver as being the cause; maybe there 
are some problems with autonegotiation between cards and switch which 
lower the performance of network transfer when using the CX cards. But you 
have to find out if this is the case by getting more specific data about 
your network.

-- 
Bogdan Costescu

IWR - Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen
Universitaet Heidelberg, INF 368, D-69120 Heidelberg, GERMANY
Telephone: +49 6221 54 8869, Telefax: +49 6221 54 8868
E-mail: [email protected]

_______________________________________________
vortex mailing list
[email protected]
http://www.scyld.com/mailman/listinfo/vortex