gomp slowness

[Joe Buck]

On Thu, Oct 18, 2007 at 03:00:02AM +1000, skaller wrote:
> Hi, I have just run and timed a couple of tutorial examples for
> openMP using gcc (GCC) 4.2.1 (Ubuntu 4.2.1-5ubuntu4) on a dual core
> Athlon amd64, with OMP_NUM_THREADS set to 1 and 2, and occasionally 
> 8 I found that 1 thread outperforms 2 by almost 2:1 on all the examples,
> and 8 is only fractionally slower than 2. The code was compiled
> with just -fopenmp, no optimisation switches. OS: Linux, Ubuntu
> gutsy (7.10) with Linux 2.26.22-14-rt (with real time patches).

Try again with optimization switches.