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Vectorize load instructions in dmmv f16 CUDA kernel (#9816)

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* Vectorize load instructions in dmmv f16 CUDA kernel

Replaces scalar with vector load instructions, which substantially
improves performance on NVIDIA HBM GPUs, e.g. gives a 1.27X overall
speedup for Meta-Llama-3-8B-Instruct-F16 BS1 inference evaluation on
H100 SXM 80GB HBM3. On GDDR GPUs, there is a slight (1.01X) speedup.

* addressed comment

* Update ggml/src/ggml-cuda/dmmv.cu

Co-authored-by: Johannes Gäßler <johannesg@5d6.de>

---------

Co-authored-by: Johannes Gäßler <johannesg@5d6.de>
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agray3 2024-10-14 01:49:08 +01:00 committed by GitHub
parent d4c19c0f5c
commit 13dca2a54a
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1 changed files with 25 additions and 9 deletions
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22
ggml/src/ggml-cuda/dmmv.cu
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@ -416,10 +416,11 @@ static __global__ void dequantize_mul_mat_vec_q6_k(const void * __restrict__ vx,
static __device__ void convert_f16(const void * vx, const int64_t ib, const int iqs, dfloat2 & v){
const half * x = (const half *) vx;
// load 2 halfs into register in a single instruction
const half2 x_reg = *((half2 *) &(x[ib + iqs]));
// automatic half -> float type cast if dfloat == float
v.x = x[ib + iqs + 0];
v.y = x[ib + iqs + 1];
v.x = __low2float(x_reg);
v.y = __high2float(x_reg);
}
static constexpr __device__ dequantize_kernel_t get_dequantize_kernel(ggml_type type) {
@ -476,13 +477,28 @@ static __global__ void dequantize_mul_mat_vec(const void * __restrict__ vx, cons
// matrix multiplication
// for qr = 2 the y index needs to increase by 1 per j iter because of y_offset = qk/2
#ifdef GGML_CUDA_F16
if ( y_offset == 1 ) {
// load 2 dfloats into register in a single instruction
const dfloat2 y_reg = *((dfloat2 *) &(y[iybs + iqs + j/qr]));
tmp += __hmul2(v, y_reg);
}
else {
tmp += __hmul2(v, {
y[iybs + iqs + j/qr + 0],
y[iybs + iqs + j/qr + y_offset]
});
}
#else
if ( y_offset == 1 ) {
// load 2 dfloats into register in a single instruction
const dfloat2 y_reg = *((dfloat2 *) &(y[iybs + iqs + j/qr]));
tmp += v.x * y_reg.x;
tmp += v.y * y_reg.y;
}
else {
tmp += v.x * y[iybs + iqs + j/qr + 0];
tmp += v.y * y[iybs + iqs + j/qr + y_offset];
}
#endif // GGML_CUDA_F16
}
}