[AMD] mir-glas is slower than OpenBLAS for DGEMM

[MigMuc]

I suceesfully compiled the benchmark gemm_report.d provided by mir-glas. I ran it twice.
One comparing with OpenBLAS and another comparing against ACML-5.3.1.
As you can see from the benchmarks mir-glas does not yield full performance for large matrices.
Peak performance for my machine is about 23 GFLOPs for double precision.
But also ACML does noch achieve full performance.
So I decided to compare with dgemm.goto and dgemm.acml benchmark programs provided in
OpenBLAS/benchmark. Here ACML reaches peak performance too. Is there any overhead calling
ACML from D?

[MigMuc]

I have llvm version 3.9.1 installed.

[9il]

Hey @MigMuc,

Is there any overhead calling ACML from D?

No, only cblas_dgemm CBLAS function are called.

I have never tested GLAS on AMD CPUs. Would be awesome to have benchmarks for AMD. Benchmarks can be posted in the blog https://github.com/libmir/blog.

Is AMD FX(TM)-4300 @ 3.8 GHz your CPU?

Possible factors that may influence performance:

1. Computation kernel structure.
2. CPU Cache usage by BLAS and other programs. You may want to close web browser and other programs to get correct benchmarks.
3. Matrix transposition.
4. Strange thermal behaviour.

Lets start with computation kernels to optimize GLAS.

OpenBLAS uses sgemm_kernel_16x2_piledriver. This is strange because this kernel do not use YMM registers, only XMM registers. Maybe Piledriver YMM are simulated on top of XMM?

To see GLAS DGEMM kernel comile this gist with -output-s flag. Command line example is in the first line. The example is for SGEMM, replace float[8] with double[4] to generate DGEMM kernel.

Thanks!

[MigMuc]

Hi @9il,

Is AMD FX(TM)-4300 @ 3.8 GHz your CPU?

Yes, it has a Piledriver core.
So in order to compile the gemm_micro_kernel.d I used the -mcpu=bdver2 flag after exchanging

11 
12 export extern(C)
13 auto dot_reg_basic_generic(
14     const(__vector(float[8])[2][1])* a,
15     const(float[1][6])* b,
16     size_t length,
17     ref __vector(float[8])[2][1][6] c,
18 )
19 {
20     return dot_reg_basic(a, b, length, c);
21 }
22 

with

11 
12 export extern(C)
13 auto dot_reg_basic_generic(
14     const(__vector(double[4])[2][1])* a,
15     const(float[1][6])* b,
16     size_t length,
17     ref __vector(double[4])[2][1][6] c,
18 )
19 {
20     return dot_reg_basic(a, b, length, c);
21 }
22 

I got the following result:

gemm_micro_kernel.s.txt

[9il]

Please replace float with double for b

[MigMuc]

gemm_micro_kernel.s.txt

[RoyiAvital]

Can one use mir-glas on Windows for C \ C++ Projects using Visual Studio?

[9il]

@RoyiAvital, yes. It has C headers. Note, that it is single thread for now.

[RoyiAvital]

@9il ,
I'm interested in Small Matrices Linear Algebra library.
Hence I'm OK, for now, with Single Threaded implementation.

Is there a guide or examples how to use it from C Code under Windows?

Thank You.

[9il]

@RoyiAvital ,

1. Build the library using dub package manager https://github.com/libmir/mir-glas#manual-compilation.
2. Include it into your project as common C library.
3. Include headers https://github.com/libmir/mir-glas/tree/master/include/glas into your project.

See also examples folder.

[MigMuc]

I spent some time doing benchmark tests and here they are:

[RoyiAvital]

@MigMuc, Could you please add label for the axis?
I'm not sure if higher or lower is better.

Thank You.