LINMA2710 - Scientific Computing Single Instruction Multiple Data (SIMD)
P.-A. Absil and B. Legat
👀 Reading hidden code
header("LINMA2710 - Scientific Computing
Single Instruction Multiple Data (SIMD)", "P.-A. Absil and B. Legat")
Motivation
👀 Reading hidden code
The need for parallelism
👀 Reading hidden code
👀 Reading hidden code
👀 Reading hidden code
A bit of historical context
👀 Reading hidden code
1972 : C language created by Dennis Ritchie and Ken Thompson to ease development of Unix (previously developed in assembly)
1985 : C++ created by Bjarne Stroustrup
2003 : LLVM started at University of Illinois
2005 : Apple hires Chris Lattner from the university
2007 : He then creates the LLVM-based compiler Clang
2009 : Mozilla start developing an LLVM-based compiler for Rust
2009 : Develpment starts on Julia, with LLVM-based compiler
👀 Reading hidden code
A sum function in C and Julia
👀 Reading hidden code
float sum(float *vec, int length) {
float total = 0;
for (int i = 0; i < length; i++) {
total += vec[i];
}
return total;
}👀 Reading hidden code
c_sum(x::Vector{Cfloat}) = ccall(("sum", sum_float_lib), Cfloat, (Ptr{Cfloat}, Cint), x, length(x));
👀 Reading hidden code
julia_sum (generic function with 1 method)function julia_sum(v::Vector{T}) where {T}
total = zero(T)
for i in eachindex(v)
total += v[i]
end
return total
end
👀 Reading hidden code
👀 Reading hidden code
Let's make a small benchmark
👀 Reading hidden code
0.112507
0.468145
0.485314
0.951905
0.334012
0.813746
0.788372
0.578425
0.59928
0.254122
0.52617
0.787783
0.600585
0.396555
0.997031
0.966838
0.211345
0.457491
0.0524767
0.709192
0.0975684
0.556911
0.121917
0.11718
0.879031
0.408504
0.853165
0.197908
0.665125
0.953368
vec_float = rand(Float32, 2^16)
👀 Reading hidden code
32784.137f0@btime c_sum($vec_float)
👀 Reading hidden code
32784.137f0@btime julia_sum($vec_float)
👀 Reading hidden code
How to speed up the C code ?
Try passing the following flags to Clang by selecting them and waiting for the benchmark timing to refresh:
What are they doing ? We'll see in the slide...
👀 Reading hidden code
👀 Reading hidden code
👀 Reading hidden code
👀 Reading hidden code
Summing with SIMD
👀 Reading hidden code
Loading cells...