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Re: gomp slowness
- From: Joe Buck <Joe dot Buck at synopsys dot COM>
- To: skaller <skaller at users dot sourceforge dot net>
- Cc: gcc at gcc dot gnu dot org
- Date: Wed, 17 Oct 2007 10:09:48 -0700
- Subject: Re: gomp slowness
- References: <1192640402.10798.11.camel@rosella.wigram>
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.