Gaius.jl
Because Caesar.jl was taken
/badge.svg "Continuous Integration (Julia nightly)"){kind=icon}
Gaius.jl is a multi-threaded BLAS-like library using a divide-and-conquer strategy to parallelism, and built on top of the fantastic LoopVectorization.jl. Gaius spawns threads using Julia's depth first parallel task runtime and so Gaius's routines may be fearlessly nested inside multi-threaded Julia programs.
Gaius is not stable or well tested. Only use it if you're adventurous.
Note: Gaius is not actively maintained and I do not anticipate doing further work on it. However, you may find it useful as a relatively simple playground for learning about the implementation of linear algebra routines.
There are other, more promising projects that may result in a scalable, multi-threaded pure Julia BLAS library such as:
In general:
- Octavian is the most performant.
- Tullio is the most flexible.
Quick Start
julia> using Gaius
julia> Gaius.mul!(C, A, B) # (multi-threaded) multiply A×B and store the result in C (overwriting the contents of C)
julia> Gaius.mul(A, B) # (multi-threaded) multiply A×B and return the result
julia> Gaius.mul_serial!(C, A, B) # (single-threaded) multiply A×B and store the result in C (overwriting the contents of C)
julia> Gaius.mul_serial(A, B) # (single-threaded) multiply A×B and return the resultRemember to start Julia with multiple threads with e.g. one of the following:
julia -t autojulia -t 4- Set the
JULIA_NUM_THREADSenvironment variable to4before starting Julia
The functions in this list are part of the public API of Gaius:
Gaius.mul!Gaius.mulGaius.mul_serial!Gaius.mul_serial
All other functions are internal (private).
Matrix Multiplication
Currently, fast, native matrix-multiplication is only implemented
between matrices of types Matrix{<:Union{Float64, Float32, Int64, Int32, Int16}}, and StructArray{Complex}. Support for other other
commonly encountered numeric struct types such as Rational and
Dual numbers is planned.
Using Gaius
Click to expand:
Gaius defines the public functions Gaius.mul and
Gaius.mul!. Gaius.mul is to be used like the regular *
operator between two matrices whereas Gaius.mul! takes in three
matrices C, A, B and stores A*B in C overwriting the contents of
C.
The functions Gaius.mul and Gaius.mul! use multithreading. If you
want to run the single-threaded variants, use Gais.mul_serial and
Gaius.mul_serial! respectively.
julia> using Gaius, BenchmarkTools, LinearAlgebra
julia> A, B, C = rand(104, 104), rand(104, 104), zeros(104, 104);
julia> @btime mul!($C, $A, $B); # from LinearAlgebra
68.529 μs (0 allocations: 0 bytes)
julia> @btime mul!($C, $A, $B); #from Gaius
31.220 μs (80 allocations: 10.20 KiB)julia> using Gaius, BenchmarkTools
julia> A, B = rand(104, 104), rand(104, 104);
julia> @btime $A * $B;
68.949 μs (2 allocations: 84.58 KiB)
julia> @btime let * = Gaius.mul # Locally use Gaius.mul as * operator.
$A * $B
end;
32.950 μs (82 allocations: 94.78 KiB)
julia> versioninfo()
Julia Version 1.4.0-rc2.0
Commit b99ed72c95* (2020-02-24 16:51 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: AMD Ryzen 5 2600 Six-Core Processor
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-8.0.1 (ORCJIT, znver1)
Environment:
JULIA_NUM_THREADS = 6Multi-threading in Gaius works by recursively splitting matrices
into sub-blocks to operate on. You can change the matrix sub-block
size by calling mul! with the block_size keyword argument. If left
unspecified, Gaius will use a (very rough) heuristic to choose a good
block size based on the size of the input matrices.
The size heuristics I use are likely not yet optimal for everyone's machines.
Complex Numbers
Click to expand:
Gaius supports the multiplication of matrices of complex numbers, but they must first by converted explicity to structs of arrays using StructArrays.jl (otherwise the multiplication will be done by OpenBLAS):
julia> using Gaius, StructArrays
julia> begin
n = 150
A = randn(ComplexF64, n, n)
B = randn(ComplexF64, n, n)
C = zeros(ComplexF64, n, n)
SA = StructArray(A)
SB = StructArray(B)
SC = StructArray(C)
@btime mul!($SC, $SA, $SB)
@btime mul!($C, $A, $B)
SC ≈ C
end
515.587 μs (80 allocations: 10.53 KiB)
546.481 μs (0 allocations: 0 bytes)
trueBenchmarks
Floating Point Performance
Click to expand:
The following benchmarks were run on this
julia> versioninfo()
Julia Version 1.4.0-rc2.0
Commit b99ed72c95* (2020-02-24 16:51 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: AMD Ryzen 5 2600 Six-Core Processor
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-8.0.1 (ORCJIT, znver1)
Environment:
JULIA_NUM_THREADS = 6and compared to OpenBLAS running with
6 threads (BLAS.set_num_threads(6)). I would be keenly interested in seeing
analogous benchmarks on a machine with an AVX512 instruction set and/or
Intel's MKL.
Note that these are log-log plots.
Gaius outperforms OpenBLAS over a large
range of matrix sizes, but
does begin to appreciably fall behind around 800 x 800 matrices for
Float64 and 650 x 650 matrices for Float32. I believe there is a
large amount of performance left on the table in Gaius and I look
forward to beating OpenBLAS for more matrix sizes.
Complex Floating Point Performance
Click to expand:
Here is Gaius operating on Complex{Float64} structs-of-arrays
competeing relatively evenly against OpenBLAS operating on
Complex{Float64} arrays-of-structs:
I think with some work, we can do much better.
Integer Performance
Click to expand:
These benchmarks compare Gaius (on the same machine as above) and compare against Julia's generic matrix multiplication implementation (OpenBLAS does not provide integer mat-mul) which is not multi-threaded.
Note that these are log-log plots.
Benchmarks performed on a machine with the AVX512 instruction set show an even greater performance gain.
If you find yourself in a high performance situation where you want to multiply matrices of integers, I think this provides a compelling use-case for Gaius since it will outperform it's competition at any matrix size and for large matrices will benefit from multi-threading.
Other BLAS Routines
I have not yet worked on implementing other standard BLAS routines with this strategy, but doing so should be relatively straightforward.
Safety
If you must break the law, do it to seize power; in all other cases observe it.
-Gaius Julius Caesar
If you use only the functions Gaius.mul!, Gaius.mul,
Gaius.mul_serial!, and Gaius.mul_serial,
automatic array size-checking will occur before
the matrix multiplication begins. This can be turned off in
mul! by calling Gaius.mul!(C, A, B; sizecheck=false), in
which case no sizechecks will occur on the arrays before the matrix
multiplication occurs and all sorts of bad, segfaulty things can
happen.
All other functions in this package are to be considered internal
and should not be expected to check for safety or obey the law. The
functions Gaius.gemm_kernel! and Gaius.add_gemm_kernel! may be of
utility, but be warned that they do not check array sizes.