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Comment by danmg | Hacker News Reader

Why aren't they showing benchmarks that compare it to other BLAS implementations? How does it compare to the GEMM in atlas, cblas, intel's mks, GOTOBlas, or any other library that implements GEMM? Is writing 'jitted' asm like this better than writing fortran with -march=native?

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FBGEMM is faster than theoretical peak FP32 (single-precision floating-point) performance, therefore its faster than SGEMM/DGEMM in any BLAS library

If they're showing something higher than a 'theoretical peak' then it's a fantastic result that must be investigated carefully for any error in data collection.

Also, that doesn't stop them from showing an apples-to-apples comparison against other libraries that provide GEMM. If other libraries are reporting the same 'beyond theoretical peak' then it most certainly is a data collection error.

Performance on the plot is higher than FP32 peak, but there's no error - because FBGEMM does not compute in FP32, it computes in 8-bit fixed point. On a Broadwell CPU, you can do 16 FP32 multiply-adds (2x 8-wide FMA instructions via VFMAxxxPS instructions), but 32 8-bit multiply adds (1x 32-wide multiplication with accumulation of adjacent results via VPMADDUSBW instruction).

Ok. Then this will introduce significant truncation errors and it's not a general GEMM. That's like claiming you've made the fastest FEM routine in the world by doing everything in half-precision.

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