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Re: gomp slowness
On Thu, 2007-10-18 at 11:18 +1000, skaller wrote:
> On Wed, 2007-10-17 at 10:09 -0700, Joe Buck wrote:
> > 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.
> OK, tried with -O2.
Argg .. oops .. -O3.
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net