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Re: OpenMP and AVX2 Problem

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"F. Russell" <fr@random.info> writes:
>I am using AVX2 intrinsics to speed up math calculations.
>For example, using AVX2 can speed up the vector cross product,
>C = A X B, by a factor of 4, which for large arrays of vectors
>is a huge boost to performance.
>
>I am now thinking of using openmp to create multi-threaded
>routines where each processor, or thread, can execute the
>same AVX2 instructions on a part of the array.  This should
>speed thing up by at least another factor of four.
>
>However, my initial attempts do not work.  In fact, using
>openmp slows the calculations down by a factor of 5.
>I must be doing something wrong but I don't know what.

My first guess would be cache contention.    Try ensuring that
all the data being operated on by a given thread is colocated
in memory (or at least 64-bytes apart from memory used by a
different thread).

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Thread

OpenMP and AVX2 Problem "F. Russell" <fr@random.info> - 2018-05-12 15:09 +0000
  Re: OpenMP and AVX2 Problem Tim Prince <tprince@intelretiree.com> - 2018-05-12 11:33 -0400
  Re: OpenMP and AVX2 Problem Melzzzzz <Melzzzzz@zzzzz.com> - 2018-05-12 16:05 +0000
    Re: OpenMP and AVX2 Problem "F. Russell" <fr@random.info> - 2018-05-12 17:46 +0000
    Re: OpenMP and AVX2 Problem "F. Russell" <fr@random.info> - 2018-05-12 19:10 +0000
  Re: OpenMP and AVX2 Problem [SOLVED] "F. Russell" <fr@random.info> - 2018-05-12 19:42 +0000
    Re: OpenMP and AVX2 Problem [SOLVED] Keith Thompson <kst-u@mib.org> - 2018-05-12 14:04 -0700
  Re: OpenMP and AVX2 Problem scott@slp53.sl.home (Scott Lurndal) - 2018-05-13 17:47 +0000
  Re: OpenMP and AVX2 Problem Wouter Verhelst <w@uter.be> - 2018-05-13 09:57 +0200

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