[cfe-dev] Bug with vectorization of transcendental functions
olaf.krzikalla at tu-dresden.de
Thu Aug 21 06:42:29 PDT 2014
Am 19.08.2014 23:31, schrieb Ian Bell:
> The example shows
> what *not* to do, would be great if you could come up with an example of
> best practices. If you could, I well might use your library. What's
> the expected speedup for AVX for instance?
You just cannot give a general answer to that question. Not even an
estimation. The only thing you can state for sure is that vectorization
shifts the performance from being compute-bound toward being
memory-bound. So if your algorithm is already memory-bound, you will not
see any effect at all (in rare circumstances it might even decrease the
performance). In other cases (e.g. reductions without any memory
footprint) you might get practical speedups above the theoretical
maximum (e.g. more than 8x for float on AVX).
It just depends on too many factors to state any expected speedups in a
best practice guide of a general-purpose library.
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