[Openmp-dev] initial clang-omp/openmp benchmarking

[Jack Howarth]

On Wed, May 28, 2014 at 10:24 AM, Cownie, James H
<james.h.cownie at intel.com>wrote:

>  Sorry, I read your description of the problem
>
> “While the results for iomp5 are far better on darwin than those for gomp
> on darwin, we still are lagging behind the performance of gomp using futex
> on linux.”
>
> as being that libiomp5.so was underperforming on Linux because we’re not
> using futex there, so I was explaining how we could do that.
>
>
>
> I now grok that what you’re saying is that you’d like to see performance
> on Darwin (without futexes) that is faster than on Linux (with futexes).
>
> So, I suggest trying the TAS lock, (KMP_LOCK_KIND=tas on Darwin).
>

Not necessarily faster on darwin but at least equal in performance to
linux. FYI, I posted the raw timings for this test case on both darwin and
linux…

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61333#c13
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61333#c14

A cursory examination suggests that the ratios of the one to four OMP
process timings are pretty much identical between the clang-omp and FSF gcc
compilers on linux but the darwin ratios on clang-omp are about 5% lower
than futex on linux and even worse for gomp on darwin.

>
>
> Depending on what you think OpenMP is used for, though, locks may be
> irrelevant. If you look at the latest SPECOMP codes, there are none that
> use locks (down from the previous version that had a couple).
>
>
>
> In HPC locks should be rare and heavily contended locks absent completely.
> (Because if there are heavily contended locks in a significant part of the
> code, it won’t perform well anyway, so doesn’t qualify for the “HPC” name
> J).
>
>
>
> -- Jim
>
> James Cownie <james.h.cownie at intel.com>
> SSG/DPD/TCAR (Technical Computing, Analyzers and Runtimes)
>
> Tel: +44 117 9071438
>
>
>
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