slow multithreading with fedora core 5
 

We have a quad dual core opteron system (i.e. 8 CPU cores in total) on which we run our multithreaded code. Previously we had Red Hat Enterprise Linux 3 running on it. I changed the system to FC5 recently and now the same multithreaded code runs much slower!
The performance dropped from 180s (on WS3) to 277s (on FC5) for exactly the same code (using all 8 cores). In single thread mode, there is no difference in performance. Any ideas?

Thanks,

Felix

Hi.

Interesting issue. I don't have an answer, but I have built a quad HT box (Windows based) which was used for testing a banks risk assessment software.

The use of the processors varied depending on the type of calculations (Floating point or integer based). Also the performance slowed down the more processors were added/used. What improved however was the load capacity the software could deal with.

So I would guess that your issues depend on how each operating system deals with the threading model, the algorithms and the load. The other thing with the banks code was that it could fit into the processor cache. Does yours have a lot of disk writes?

Just a thought...don't know if the above is of any real value to yourselves!

Richard

slow multithreading
 

The program does not fit into the cache, so yes we have a lot of regular memory access. The system has 32GByte of ram, so no disk access at all. What is weird though is, that we "only" changed from one older to linux version to the latest and see these performance losses. Could it possibly be related to the fact that we use a generic 64 bit kernel?

Quite probably. The SMP kernels are 'endowed' with NPTL (Multi Processor Threading).

Do a search on kernel-smp in yum or pirut.

The latest kernel from what I can see is kernel-smp-2.6.17-1.2174

Red Hat Enterprise Linux costs at least US$350.

Fedora Core is free.

If they both behaved the same then nobody would pay for the Enterprise Server version.

Fedora Core is intended to be a demo/workstation system. What you have achieved is to prove that you do get a better tuned system from Red Hat when you pay US$350 compared to using their free software.

Given that you have spent a huge amount of money on the hardware it makes sense to spend some money on one of the enterprise versions of Linux or go back to the version of RHEL that you had been using. I can't imagine what inspired you to make the change in the first place.