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Subject: Re: [ublas] uBlas and OpenMP
From: rrossi_at_[hidden]
Date: 2011-03-28 17:35:09


Hi All,

 i believe that including OpenMP in ublas is potentially
very interesting, nevertheless how will you ensure

that openmp is used
only for large matrices and vectors without providing a performance
penalty for small matrices/vectors?

For example i use ublas dense
matrices inside parallel regions, so if you put openmp inside that you
would destroy the performance of my code...

maybe one solution would
be to define a parallel matrix/vector so that the user can explicitly
use it. Indeed currently what we do is that we redefine the axpy product
and the dots

so that we can use them ONLY when we like them to be

As a secondary comment please consider that in order to
squeeze performance from modern machines it is FUNDAMENTAL to do
allocation in parallel...

well...all for now



On Tue, 29 Mar 2011 00:20:08 +0400, Matwey V. Kornilov wrote:

> Try
to change number of active threads, for instance type:
> export
> before running your programm. Due to OpenMP
scheduling there is possible
> performance degeneracy with increasing
of threads.
> Nasos Iliopoulos wrote:
>> Great to know! I don't
feel that the example I posted earlier is by any means complete,
optimized or whatever. I just pointed out the locations in uBlas one may
want to start looking to add OpenMP parallelization into it. In any case
if you have any further experience to share it would be very useful!
Thanks, Nasos
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