4 ms·
SLEEF Vectorized Math Library
- svantana 7y agoInteresting, but a bit weird that the benchmark doesn't include the standard math functions - the question most potential users would ask is, how much performance could I gain from this? Personally I do a lot of approximations of math functions, which usually give me about a 10x speed increase relative to <math.h>. From the looks of it, this isn't quite that fast.
- someguydave 7y agoThis is more for people who need to do specialized DSP math like DFTs using a variety of different cpu arches. Most vendor libraries (like Intel IPP) for vector units fail to support their competitors. So benchmarks might be relatively less important than portability.
- kcbanner 7y agoThis library can leverage data parallelism to increase throughout vs the scalar versions. ie. One instruction performs 4 operations instead of one. If the problem you are solving is suited to this parallelism, you could get a significant speedup.
- svantana 7y agoSure, so why is that speedup not measured in the benchmark?
- celrod 7y agoRecent versions of GCC as well as the Intel compilers can autovectorize with the right flags (-ffast-math with GCC, -fast with Intel), and yield better performance with the <math.h> functions than you'll get from SLEEF on x86_64. LLVM doesn't have a vector math library, so SLEEF could help you there. If you're using single precision and AVX512, a >10x speed increase is likely. Otherwise, you'll probably get less than that. These functions are very accurate, most to withing 1 ULP of least precision. That is, if the answer they provide isn't the correctly rounded floating point answer, then it'll be either the next or previous representable floating point number. There is a lot of room for giving up accuracy in the name of speed (eg, using less terms in the polynomials).
- svantana 7y agoDo you have a benchmark showing that gcc is faster than sleef? Sorry I wasn't clear, by "10x" I meant 10x faster than the standard library with the fastest compiler options (-O3 -ffast-math -avx512), but I've only tested with clang.
- gameswithgo 7y agoi use this library as an optional feature in simdeez. it was a relief to find it, and a rust wrapper for it. its hard stuff to port it is so arcane. big thanks to sleef!
- celrod 7y agoI've been relying on a Julia port of version 2 (version 3 is out now). Version 3 added a lot of new functions, and I believe it improved performance on many of the old ones. It is much faster (when vectorized) than what you get in base Julia, but lags behind gcc (glibc) and the Intel compiler's vectorized math libraries in performance.
- improbable22 7y agoCurious whether you've compared it to https://github.com/chriselrod/LoopVectorization.jl https://github.com/chriselrod/LoopVectorization.jl ? Which if I understand right is a pure-Julia attempt to use many of the same tricks.
- celrod 7y agoCompare my username with that of the author of that library ;). For special functions, LoopVectorization relies on SLEEFPirates.jl, which is a fork of SLEEF.jl, a Julia port of version 2 of SLEEF. Most of the changes in SLEEFPirates are so that it works when you use llvm-vectors as arguments, but I also switched to using Estrin's rather than Horner's method of evaluating polynomials for a few functions (which more recent SLEEF versions did as well). The code is pure Julia (or Julia + LLVM call; either way it does not need any external dependencies aside from Julia itself). It does need performance work, but I have many higher priorities at the moment.
- improbable22 7y agoHah! Sorry, didn't cross my mind. And thanks for the details.
- 7y ago