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Pre-fetch next column block in int8 GEMV #561

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Jan 29, 2025
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Pre-fetch next column block in int8 GEMV #561

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15 changes: 11 additions & 4 deletions src/gemm/kernels/simd_generic.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -604,10 +604,12 @@ pub unsafe fn simd_int8_gemv<S: SimdInt, const CAST_B_U8: bool>(
// D0 D1 D2 D3
//
// The second tile contains A4..A7 and so on.
let b0 = S::load(b_ptr.add(k * b_row_stride) as *const i32);
let b1 = S::load(b_ptr.add((k + 1) * b_row_stride) as *const i32);
let b2 = S::load(b_ptr.add((k + 2) * b_row_stride) as *const i32);
let b3 = S::load(b_ptr.add((k + 3) * b_row_stride) as *const i32);
let b_tile_ptr: [*const i32; 4] =
std::array::from_fn(|i| b_ptr.add((k + i) * b_row_stride) as *const i32);
let b0 = S::load(b_tile_ptr[0]);
let b1 = S::load(b_tile_ptr[1]);
let b2 = S::load(b_tile_ptr[2]);
let b3 = S::load(b_tile_ptr[3]);

let b01_lo = b0.zip_lo_i8(b1);
let b01_hi = b0.zip_hi_i8(b1);
Expand All @@ -621,6 +623,11 @@ pub unsafe fn simd_int8_gemv<S: SimdInt, const CAST_B_U8: bool>(
b01_hi.zip_hi_i16(b23_hi),
];

// Pre-fetch the current block of 4 rows for the next column tile.
for i in 0..4 {
S::prefetch(b_tile_ptr[i].add(S::LEN));
}

for i in 0..4 {
let b_tile = if CAST_B_U8 {
b_tiles[i].xor(bit_flip_mask)
Expand Down