ViperEkura
f45230fb2c
- fold the two adjacent nt B fragments of each pair into one ldmatrix.x4: lanes 0-7/8-15 address rows n0..n7 chunks c/c+1, lanes 16-23/24-31 the same chunks of rows n8..n15, so {r0,r1} feed the even nt mma and {r2,r3} the odd nt — 4 x4 B loads per k-tile instead of 8 x2 (12 LDSM total, matching the decompiled cuBLAS and CUTLASS loop shapes)
- the +8-row half never reaches the XOR-swizzle source bits for kK <= 64 (row[2:1]), so the pairing rides the existing per-lane address closure with one extra term (rh16 * 8 * kK); kK=128 swizzles on row[2:0] and keeps the x2 path
- decompilation trail: nsys shows cuBLAS never split-Ks on the gap shapes (grid.z=1, no atomics; it fills waves with 64x128/64x64 tiles instead), and a CUTLASS 3.8 reference at our exact 128x128 s3 geometry reaches 196.5T at 2048^3 vs our 177.9T with NOP=0 and 12 LDSM — proving the loop shape is reachable from CUDA C++ (see perf/fp8_next_ideas.md F/C)
Benchmark: L20 (sm_89), kernel-level sweep: 2048^3 176.7->178.1T, 4096^3 196.3->197.2T, 8192^3 ->208.7T, 4096x512x4096 137.3->139.1T, 896x1152x4096 121->123.4T. CUDA-graph e2e: 512^3 54.2->55.3T, 1536^3 142.3->143.4T, 2048^3 177.9->179.4T, 8192^3 198.2->199.0T. Four-layout C++ suite, 596 pytests pass.
897 lines
47 KiB
Plaintext
897 lines
47 KiB
Plaintext
#pragma once
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// FP8 GEMM device code — pure CUDA, no torch. Mirrors the attention kernel
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// layout (attn_*_mma.cuh): kernels take the FP8Params POD, tile shape and
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// FP8 format ride on compile-time template parameters, and launchers are
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// plain functions usable from both the torch binding and pure C tests. The
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// quantize kernel lives in quantize.cuh.
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#include <cuda_bf16.h>
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#include <cuda_fp8.h>
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#include <cuda_runtime.h>
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#include <type_traits>
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#include "common.h"
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#include "../common/cp_async.cuh"
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#include "../common/mma.cuh"
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#include "../common/reduce.cuh"
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namespace astrai {
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namespace fp8 {
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// m16n8k32 (see astrai::mma_shape<fp8 type>::k in common/mma.cuh)
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constexpr int kMmaK = 32;
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// log2 of a compile-time power of two (for tile_at's swizzle shift).
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template <int N, int Acc = 0>
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struct log2_const : log2_const<(N >> 1), Acc + 1> {};
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template <int Acc>
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struct log2_const<1, Acc> {
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static constexpr int value = Acc;
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};
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// ---------------------------------------------------------------------------
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// Shared device helpers
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// ---------------------------------------------------------------------------
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// FP8 MMA lives in the shared astrai::mma_sync template (common/mma.cuh);
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// instantiate it with the kernel's T8. Accumulates in-place: callers pass
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// the same accumulator array as both `d` and `c`.
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// The cp.async pipeline primitives (predicated 16-byte copy, commit_group,
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// wait_group + runtime dispatch) live in common/cp_async.cuh.
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// ---------------------------------------------------------------------------
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// Swizzled address inside a flat [rows * K] staging tile: the 16-byte chunk
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// index is XORed with a row-dependent slice so a warp's fragment load (8
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// consecutive rows x 16B) hits all 32 banks exactly once. With kChunks
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// power-of-two chunks per row, the XOR source is the top log2(kChunks) bits
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// of the row index within each group of 8:
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// kChunks=2 -> row bits [3] (K=32: rows r and r+4 diverge)
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// kChunks=4 -> row bits [2:1] (K=64: rows diverge every 2)
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// kChunks=8 -> row bits [2:0] (K=128: every row)
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// (row word-stride is K/4 words = 4*kChunks, so unswizzled rows r and
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// r + 8/kChunks collide mod 32 banks; the XOR spreads the 8 rows of one
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// ldmatrix matrix across the 8 distinct 4-bank groups.) Chunks stay
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// contiguous, so the cp.async 16B staging path is unaffected.
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template <int K, typename T8>
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__device__ __forceinline__ T8* tile_at(T8* tile, int row, int col) {
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constexpr int kChunks = K / 16; // 16B chunks per row
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static_assert(kChunks >= 1 && (kChunks & (kChunks - 1)) == 0,
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"swizzle needs a power-of-two 16B-chunk count");
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constexpr int kShift = 3 - log2_const<kChunks>::value;
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return tile + row * K +
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((((col >> 4) ^ ((row >> kShift) & (kChunks - 1))) << 4) + (col & 15));
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}
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// Stage-load a CONGRUOUS operand (stored [rows][contract], contract-
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// contiguous — the only cp.async-able shape for the canonical tile) into the
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// flat [rows * K] shared tile via tile_at's swizzle. Crosswise operands go
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// through load_crosswise_direct instead.
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template <typename T8, int K, int RowsTile, int kThreads>
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__device__ __forceinline__ void
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load_operand_tile(T8* tile, const T8* __restrict__ operand, int64_t rows,
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int64_t contract, int64_t ld, int tid, int64_t k_base,
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int64_t block_row) {
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constexpr int kChunks = K / 16;
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static_assert(RowsTile * kChunks % kThreads == 0,
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"tile chunks must divide evenly across threads");
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constexpr int kCpt = RowsTile * kChunks / kThreads; // chunks per thread
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// Linear chunk mapping: thread covers kCpt consecutive 16B chunks of
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// one row (K=64: a contiguous 32B pair; K=32: a single chunk).
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constexpr int kCpr = kChunks / kCpt; // chunks per row slice
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const int r = tid / kCpr;
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const int c0 = (tid % kCpr) * kCpt * 16;
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const int64_t row = block_row + r;
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const bool row_ok = row < rows;
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// k_base and every c are multiples of 16, so the per-chunk sources
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// share the row base's alignment.
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const auto* src = operand + row * ld + k_base;
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const bool chunk_aligned = (reinterpret_cast<uintptr_t>(src) & 15) == 0;
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#pragma unroll
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for (int j = 0; j < kCpt; ++j) {
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const int c = c0 + j * 16;
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T8* dst = tile_at<K>(tile, r, c);
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if (row_ok && chunk_aligned && k_base + c + 15 < contract) {
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astrai::cp_async_16(dst, src + c, true);
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} else {
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// Tail chunk (or misaligned base): predicated scalar fill.
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#pragma unroll
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for (int i = 0; i < 16; ++i)
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dst[i] =
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row_ok && k_base + c + i < contract ? src[c + i] : T8(0.0f);
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}
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}
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}
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// Interior-tile congruous load: zero predication. Valid when
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// block_row + RowsTile <= rows, k_base + K <= contract and
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// (operand base | ld | k_base) is 16B-aligned — the kernel's fast_cta peel
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// guarantees all three. With n = a thread's first chunk a multiple of kCpt,
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// (n+j)^swz == (n^swz)^j, so the swizzled destination of chunk j is the
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// base pointer XOR (j << 4): the whole address math folds into one
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// immediate XOR per chunk (~3 inst/chunk vs ~9 predicated).
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template <typename T8, int K, int RowsTile, int kThreads>
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__device__ __forceinline__ void
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load_operand_tile_interior(T8* tile, const T8* __restrict__ operand,
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int64_t ld, int tid, int64_t k_base,
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int64_t block_row) {
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constexpr int kChunks = K / 16;
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static_assert(RowsTile * kChunks % kThreads == 0,
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"tile chunks must divide evenly across threads");
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constexpr int kCpt = RowsTile * kChunks / kThreads;
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constexpr int kCpr = kChunks / kCpt;
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const int r = tid / kCpr;
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const int c0 = (tid % kCpr) * kCpt * 16;
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const char* src = reinterpret_cast<const char*>(
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operand + (block_row + r) * ld + k_base + c0);
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const uintptr_t dst = reinterpret_cast<uintptr_t>(tile_at<K>(tile, r, c0));
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#pragma unroll
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for (int j = 0; j < kCpt; ++j)
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astrai::cp_async_16(reinterpret_cast<T8*>(dst ^ (j << 4)),
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src + j * 16, true);
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}
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// ---------------------------------------------------------------------------
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// Pre-quantized GEMM kernel: FP8 A/B read straight into shared memory, FP32
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// accumulation, BF16 or FP8 output. The input format follows Traits; the
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// tile is compact (row = kK bytes) so MMA fragments read directly — no
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// in-kernel transpose of the operands (the binding handles transposes).
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// ---------------------------------------------------------------------------
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// Direct (synchronous) crosswise load into a canonical rotating stage:
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// LDG.128 x4 (4 consecutive contract bytes x 16 rows) + in-register PRMT
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// transpose + 16 STS.32. Crosswise operands cannot cp.async into the
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// canonical [rows][contract] tile (a 16B global run holds one contract byte
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// for each of 16 rows), so they take this path. A staged variant
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// (cp.async into K-major staging + per-tile smem->smem transpose) measured
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// 15-20% SLOWER than this direct load across every probed shape, including
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// DRAM-streaming B operands — see git history (5745c2f) if it ever needs
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// revisiting for other SKUs.
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template <typename T8, int K, int RowsTile, int kThreads>
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__device__ __forceinline__ void
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load_crosswise_direct(T8* tile, const T8* __restrict__ operand, int64_t rows,
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int64_t contract, int64_t ld, int tid, int64_t k_base,
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int64_t block_row) {
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constexpr int kQuads = K / 4; // 4-byte contract quads per tile
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constexpr int kGroups = RowsTile / 16;
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constexpr int kTChunks = kQuads * kGroups; // 64B chunks per tile
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// r0 is always a multiple of 16 (block_row is a multiple of RowsTile and
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// each group covers 16 rows), and p*ld keeps the base 16B-aligned
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// whenever ld is, so every run of a chunk shares one alignment verdict.
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const bool run_aligned =
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((reinterpret_cast<uintptr_t>(operand) | ld) & 15) == 0;
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for (int chunk = tid; chunk < kTChunks; chunk += kThreads) {
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const int quad = chunk / kGroups;
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const int rg = chunk % kGroups;
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const int64_t r0 = block_row + rg * 16;
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const bool rows_full = r0 + 15 < rows;
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if (rows_full && run_aligned) {
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const int64_t p0 = k_base + quad * 4;
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uint4 v[4];
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#pragma unroll
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for (int s = 0; s < 4; ++s) {
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// Contract tail: a run past k carries zero bytes; they flow
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// through the PRMT transpose like any other value.
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if (p0 + s < contract)
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v[s] = *reinterpret_cast<const uint4*>(
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operand + (p0 + s) * ld + r0);
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else
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v[s] = make_uint4(0u, 0u, 0u, 0u);
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}
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const unsigned* bytes = reinterpret_cast<const unsigned*>(v);
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#pragma unroll
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for (int i = 0; i < 16; ++i) {
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// word i = row r0+i's quad: byte i of each of the four runs
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// [v0.b(i), v1.b(i), v2.b(i), v3.b(i)]. Byte i of a uint4
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// lives in its (i>>2)-th 32-bit register.
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const unsigned nib = i & 3;
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const unsigned sel = nib | ((nib + 4) << 4);
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const unsigned w01 =
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__byte_perm(bytes[0 + (i >> 2)], bytes[4 + (i >> 2)], sel);
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const unsigned w23 =
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__byte_perm(bytes[8 + (i >> 2)], bytes[12 + (i >> 2)], sel);
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*reinterpret_cast<unsigned*>(tile_at<K>(tile, rg * 16 + i,
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quad * 4)) =
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__byte_perm(w01, w23, 0x5410u);
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}
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} else {
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// Row-tail or misaligned chunk: byte-granular gather with
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// per-row predication; contract-tail columns zero-fill.
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#pragma unroll
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for (int s = 0; s < 4; ++s) {
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const int col = quad * 4 + s;
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if (k_base + col >= contract) {
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#pragma unroll
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for (int i = 0; i < 16; ++i)
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*tile_at<K>(tile, rg * 16 + i, col) = T8(0.0f);
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continue;
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}
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#pragma unroll
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for (int i = 0; i < 16; ++i) {
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const int64_t r_idx = r0 + i;
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*tile_at<K>(tile, rg * 16 + i, col) =
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r_idx < rows
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? operand[(k_base + col) * ld + r_idx]
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: T8(0.0f);
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}
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}
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}
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}
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}
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// Layout-aware shared-memory budget and occupancy hint. Canonic rings hold
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// kStages+1 buffers (LeanRing=false): the load for tile i+kStages targets
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// slot (i-1)%(kStages+1) — already consumed — so the pure-congruous path
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// needs no post-compute barrier (one __syncthreads per k-tile). LeanRing
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// keeps the ring at kStages buffers for small CTAs whose occupancy comes
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// from more resident CTAs (less smem) rather than a deeper rotation; it
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// brings back barrier 4.
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// The 48KB static-smem watermark picks the resident-CTA hint for
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// __launch_bounds__ (sm_89: 100KB smem per SM, so two CTAs fit while each
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// stays within the static budget).
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template <typename Traits, typename LayoutA, typename LayoutB,
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bool LeanRing = false>
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struct Fp8GemmSmem {
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// Crosswise (direct-load) operands: A ColMajor storage, B RowMajor
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// storage (B's tag is relative to the canonical [K][N]).
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static constexpr bool kDirectA = std::is_same_v<LayoutA, ColMajor>;
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static constexpr bool kDirectB = std::is_same_v<LayoutB, RowMajor>;
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// LeanRing shrinks only the congruous (async) operand rings; a direct
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// operand's ring stays kStages+1 deep (see the kernel's ring note).
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static constexpr int kARing = kDirectA ? Traits::kStages + 1
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: Traits::kStages + !LeanRing;
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static constexpr int kBRing = kDirectB ? Traits::kStages + 1
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: Traits::kStages + !LeanRing;
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static constexpr int kBytes =
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kARing * Traits::kBlockM * Traits::kK +
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kBRing * Traits::kBlockN * Traits::kK;
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static constexpr int kMinCtas = kBytes <= 48 * 1024 ? 2 : 1;
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};
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// LayoutA / LayoutB tag the operands' storage (CUTLASS-style, see common.h):
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// A RowMajor = [M][K] / ColMajor = [K][M]; B RowMajor = [K][N] /
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// ColMajor = [N][K]. The kernel always computes
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// out[m][n] = sum_p tileA[m][p] * tileB[n][p]
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// with the tiles materialized in the canonical [M][kK] / [N][kK] layout, so the
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// MMA fragments are read identically regardless of layout. The tags only
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// change how the stage-load gathers the operand from global memory:
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// A ColMajor: tileA[m][p] = a[p*a_ld + m]; A RowMajor: a[m*a_ld + p]
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// B RowMajor: tileB[n][p] = b[p*b_ld + n]; B ColMajor: b[n*b_ld + p]
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// BlockM x BlockN CTA as (BlockM/64) x (BlockN/32) warps of 64x32 warp tiles
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// (mt x nt = 4x4 MMA each). The 64x128 variant runs 4 warps / 128 threads and
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// exists for small-M calls: m <= 64 wastes half of every 128-row CTA, so the
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// launcher dispatches to it there (see launch_fp8_gemm).
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template <typename Traits, typename LayoutA = RowMajor, typename LayoutB = RowMajor, int kRasterGroup = 0,
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bool kLeanRing = false, bool kStreamOut = false,
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bool kFastLoop = false>
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__global__ void __launch_bounds__(Traits::kCtaThreads,
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Fp8GemmSmem<Traits, LayoutA, LayoutB,
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kLeanRing>::kMinCtas)
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fp8_gemm_kernel(FP8Params p) {
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using T8 = std::conditional_t<Traits::kIsE5M2, __nv_fp8_e5m2, __nv_fp8_e4m3>;
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constexpr int kBlockM = Traits::kBlockM;
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constexpr int kBlockN = Traits::kBlockN;
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constexpr int kK = Traits::kK;
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constexpr int kStages = Traits::kStages;
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constexpr int kCtaThreads = Traits::kCtaThreads;
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constexpr bool kDirectA =
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Fp8GemmSmem<Traits, LayoutA, LayoutB, kLeanRing>::kDirectA;
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constexpr bool kDirectB =
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Fp8GemmSmem<Traits, LayoutA, LayoutB, kLeanRing>::kDirectB;
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static_assert(kStages >= 1 && kStages <= 8,
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"FP8 GEMM stages must be in [1, 8]");
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// Tiles are flat [rows * kK] with a 16B-chunk XOR swizzle (tile_at):
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// ldmatrix reads whole 16B chunks through the same mapping the staging
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// writes, and the swizzle removes the bank conflict the unswizzled
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// 8-word row stride caused (see tile_at). The stages live in dynamic
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// shared memory so deep pipelines (kStages * (kBlockM + kBlockN) * kK >
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// 48KB static limit) opt in via cudaFuncSetAttribute in the launcher.
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extern __shared__ __align__(16) char fp8_gemm_smem[];
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// Per operand: congruous = kStages+1 rotating canonical buffers — the
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// load for tile i+kStages targets slot (i-1)%(kStages+1), which compute
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// finished reading before this iteration's barrier 1, so NO post-compute
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// barrier is needed on the pure-congruous path (one __syncthreads per
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// k-tile, the classic multistage rotation); direct-crosswise rotates the
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// same kStages+1 ring for the same reason.
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constexpr int kAStageBytes = kBlockM * kK;
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constexpr int kBStageBytes = kBlockN * kK;
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// Direct-crosswise operands always rotate kStages+1 buffers: their
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// prefetch issues right after barrier 1 (targeting the slot compute(i-1)
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// released), so a kStages-deep lean ring would race the in-flight MMA
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// reads. The lean ring applies only to congruous operands, whose cp.async
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// prefetch sits behind the restored barrier 4.
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constexpr int kARing = kDirectA ? kStages + 1 : kStages + !kLeanRing;
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constexpr int kBRing = kDirectB ? kStages + 1 : kStages + !kLeanRing;
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T8* const a_base = reinterpret_cast<T8*>(fp8_gemm_smem);
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T8* const b_base =
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reinterpret_cast<T8*>(fp8_gemm_smem + kARing * kAStageBytes);
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// Batch slice (grid.z): broadcast operands carry a 0 stride, so the
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// same pointer serves every batch.
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const auto* a = reinterpret_cast<const T8*>(p.a_ptr) +
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(int64_t)blockIdx.z * p.a_batch_stride;
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const auto* b = reinterpret_cast<const T8*>(p.b_ptr) +
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(int64_t)blockIdx.z * p.b_batch_stride;
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auto* out_bf16 = reinterpret_cast<__nv_bfloat16*>(p.out_ptr) +
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(int64_t)blockIdx.z * p.out_batch_stride;
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const int64_t m = p.m, n = p.n, k = p.k;
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const int64_t a_ld = p.a_ld, b_ld = p.b_ld;
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const int tid = threadIdx.x;
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const int warp = tid >> 5;
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const int lane = tid & 31;
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const int group = lane >> 2;
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const int thread_in_group = lane & 3;
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// Tile scheduler: the linear CTA id maps to (block_m, block_n) in
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// grouped (L2-friendly, CUTLASS-style) or plain raster order — the
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// grouped order makes consecutive CTAs cover a group of kRasterGroup
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// M-tiles before advancing along N, so all CTAs of one group share the
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// same B column stripe and B tiles stay hot in L2 across the wave (the
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// plain N-fastest order makes each wave touch every B tile instead;
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// kRasterGroup=0 selects plain, the measured best for dX's crosswise-B
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// layouts where grouping measured neutral).
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// Persistent schedules (static round-robin and an atomic ticket
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// dispenser, grid capped at the resident CTAs) were both measured and
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// rejected on L20: the stride desynchronizes the in-flight window
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// (-4..-8%), and the ticket variant recovers the L2 locality but lands
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// within noise of plain waves (its loop-head barrier costs what the
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// CTA-restart overlap saves). Keep the classic retiring-wave launch.
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int block_m, block_n;
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if constexpr (kRasterGroup > 0) {
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constexpr int kGroupM = kRasterGroup;
|
|
const int blocks_m = gridDim.y;
|
|
const int bid = blockIdx.y * gridDim.x + blockIdx.x;
|
|
const int group_first_m = (bid / (kGroupM * gridDim.x)) * kGroupM;
|
|
const int group_rows =
|
|
min(blocks_m - group_first_m, kGroupM); // M-tail group is short
|
|
block_m = group_first_m + bid % group_rows;
|
|
block_n = (bid % (kGroupM * gridDim.x)) / group_rows;
|
|
} else {
|
|
block_m = blockIdx.y;
|
|
block_n = blockIdx.x;
|
|
}
|
|
// CTA = (BlockM/WarpM) x (BlockN/WarpN) warps of WarpM x WarpN tiles,
|
|
// each warp computing (WarpM/16) x (WarpN/8) m16n8k32 MMAs (mt x nt).
|
|
// The default 128x128 CTA runs 8 warps of 64x32 (mt x nt = 4x4); the
|
|
// small-shape path uses 64x64 CTAs of 32x32 warps (cuBLAS-style) so more
|
|
// CTAs fit per SM (see launch_fp8_gemm).
|
|
constexpr int kMt = Traits::kWarpM / 16; // 16-row MMA tiles per warp
|
|
constexpr int kNt = Traits::kWarpN / 8; // 8-col MMA tiles per warp
|
|
constexpr int kSegs = kK / kMmaK; // mma-sized k segments per tile
|
|
const int warp_m = warp / Traits::kWarpsN;
|
|
const int warp_n = warp % Traits::kWarpsN;
|
|
const int a_row0 = warp_m * Traits::kWarpM; // + mt * 16 in the loop
|
|
const int b_row0 = warp_n * Traits::kWarpN; // + nt * 8
|
|
const float scale = *p.scale;
|
|
float acc[kNt][kMt][4] = {}; // [nt][mt][acc]
|
|
|
|
// Both operands end up in the canonical [M][kK] / [N][kK] shared tiles
|
|
// the MMA fragments read, regardless of their global layout. A's tag
|
|
// already names the operand view ([M][K] = [rows][contract]); B's tag is
|
|
// relative to the canonical [K][N], so the stage-load sees its transpose
|
|
// (transpose_layout_t, see common.h). Congruous operands cp.async
|
|
// straight into their rotating canonical buffers; crosswise operands
|
|
// take load_direct's LDG+PRMT path below.
|
|
// Asynchronous loads for tile `tile`: congruous operands cp.async into
|
|
// their canonical rings. Called after the post-compute barrier, alongside
|
|
// the commit.
|
|
auto load_async = [&](int64_t tile) {
|
|
const int64_t k_base = tile * kK;
|
|
if constexpr (!kDirectA)
|
|
load_operand_tile<T8, kK, kBlockM, kCtaThreads>(
|
|
a_base + (tile % kARing) * kAStageBytes, a, m, k, a_ld, tid,
|
|
k_base, (int64_t)block_m * kBlockM);
|
|
if constexpr (!kDirectB)
|
|
load_operand_tile<T8, kK, kBlockN, kCtaThreads>(
|
|
b_base + (tile % kBRing) * kBStageBytes, b, n, k, b_ld, tid,
|
|
k_base, (int64_t)block_n * kBlockN);
|
|
};
|
|
// Predication-free interior variant of load_async: congruous operands
|
|
// with full CTA rows, aligned (base | ld), k_base + kK <= k. fast_cta
|
|
// admits only congruous operands, so no crosswise fallback is needed.
|
|
auto load_async_fast = [&](int64_t tile) {
|
|
const int64_t k_base = tile * kK;
|
|
if constexpr (!kDirectA)
|
|
load_operand_tile_interior<T8, kK, kBlockM, kCtaThreads>(
|
|
a_base + (tile % kARing) * kAStageBytes, a, a_ld, tid, k_base,
|
|
(int64_t)block_m * kBlockM);
|
|
if constexpr (!kDirectB)
|
|
load_operand_tile_interior<T8, kK, kBlockN, kCtaThreads>(
|
|
b_base + (tile % kBRing) * kBStageBytes, b, b_ld, tid, k_base,
|
|
(int64_t)block_n * kBlockN);
|
|
};
|
|
// Synchronous direct-crosswise loads for tile `tile` into the operand's
|
|
// (kStages+1)-deep canonical ring. In the steady state this runs right
|
|
// after barrier 1, so the LDG latency and the PRMT transpose overlap the
|
|
// MMA phase of the current tile instead of stalling the inter-barrier
|
|
// window (which dominated the dX/dW stall profile: barrier 3.7-4.1 +
|
|
// long-scoreboard 1.6-1.8 stalls per issue on the production shapes).
|
|
// Ring safety: the write targets buffer (i+kStages)%(kStages+1) =
|
|
// (i-1)%(kStages+1), which compute(i-1) finished reading before the
|
|
// previous barrier and compute(i+kStages) does not touch until several
|
|
// barriers later.
|
|
auto load_direct = [&](int64_t tile) {
|
|
const int64_t k_base = tile * kK;
|
|
if constexpr (kDirectA)
|
|
load_crosswise_direct<T8, kK, kBlockM, kCtaThreads>(
|
|
a_base + (tile % kARing) * kAStageBytes, a, m, k, a_ld, tid,
|
|
k_base, (int64_t)block_m * kBlockM);
|
|
if constexpr (kDirectB)
|
|
load_crosswise_direct<T8, kK, kBlockN, kCtaThreads>(
|
|
b_base + (tile % kBRing) * kBStageBytes, b, n, k, b_ld, tid,
|
|
k_base, (int64_t)block_n * kBlockN);
|
|
};
|
|
|
|
const int64_t tile_count = (k + kK - 1) / kK;
|
|
// Interior-CTA peel (kFastLoop instantiations only): when both operands
|
|
// are congruous, whole-CTA, 16B-aligned and K has no tail, the mainloop
|
|
// runs a compile-time-specialized copy whose loads carry no predication
|
|
// — the per-chunk guards cost ~6 of ~100 instructions per warp per
|
|
// k-tile, and the small-CTA path is issue-bound there (measured
|
|
// +4.5..10% on 256³..1024³; the 128x128 kernel regressed ~3% with the
|
|
// same change, so only the small CTA opts in). All verdicts are uniform
|
|
// per CTA: one branch picks the loop copy.
|
|
const bool fast_cta =
|
|
kFastLoop && !kDirectA && !kDirectB &&
|
|
((int64_t)block_m * kBlockM + kBlockM <= m) &&
|
|
((int64_t)block_n * kBlockN + kBlockN <= n) &&
|
|
((reinterpret_cast<uintptr_t>(a) | (uint64_t)a_ld) & 15) == 0 &&
|
|
((reinterpret_cast<uintptr_t>(b) | (uint64_t)b_ld) & 15) == 0 &&
|
|
(k % kK) == 0;
|
|
|
|
// Per-lane ldmatrix fragment addressing (base-pair scheme, mirrored from
|
|
// the cuBLAS SASS: one base register per operand per k_seg, every
|
|
// fragment offset an LDSM immediate — zero address arithmetic inside the
|
|
// MMA phase). The closure works because the XOR swizzle's source bits
|
|
// come only from the lane's row-within-matrix (r7): the 8- and 16-row
|
|
// fragment steps (nt*8, mt*16) never reach them, so
|
|
// addr(s, mt) = lane_base + mt*(16*kK) ^ (s<<5) [A, x4 fragment]
|
|
// addr(s, nt) = lane_base + nt*(8*kK) ^ (s<<5) [B, x2 fragment]
|
|
// where the ^ (s<<5) lands inside the 16B-chunk swizzle field (each k_seg
|
|
// advances the chunk index by 2 = 32B) and the step lands outside it.
|
|
// kChunks=4 (K=64): swizzle bits = row[2:1] = r7[2:1]
|
|
// kChunks=8 (K=128): swizzle bits = row[2:0] = r7[2:0]
|
|
// kChunks=2 (K=32): swizzle bit = row[2] = r7[2] (single k_seg)
|
|
// Replaces the former a_off[kSegs][kMt]/b_off[kSegs][kNt] runtime tables
|
|
// (16 registers + one IADD per LDSM): at 131 regs the tables spilled and
|
|
// ptxas rematerialized every address each k-tile (~55 of 146 hot-loop
|
|
// instructions were LOP3/IMAD address math; cuBLAS's inner loop has ~0).
|
|
const int r7 = lane & 7; // row within the 8-row matrix
|
|
const int rh8 = (lane >> 3) & 1; // +8 rows (A: lanes 8-15, 24-31)
|
|
const int rh16 = lane >> 4; // +1 chunk (A: lanes 16-31; B uses rh8)
|
|
constexpr int kChunks = kK / 16;
|
|
constexpr int kShift = 3 - log2_const<kChunks>::value; // tile_at's shift
|
|
const unsigned lswz =
|
|
static_cast<unsigned>((r7 >> kShift) & (kChunks - 1));
|
|
constexpr unsigned kMtStep = 16 * kK; // bytes per m-tile row step
|
|
constexpr unsigned kNtStep = 8 * kK; // bytes per n-tile row step
|
|
constexpr unsigned kSegXor = 32; // chunk-index +2 per k_seg
|
|
// Stage-relative, loop-invariant per-lane bases (added to each ring
|
|
// slot's converted base once per k-tile). A's fragment row carries the
|
|
// +8-row half (rh8) and the +1-chunk half (rh16); B's carries rh8 as its
|
|
// chunk half — matching the m16n8k32 operand layouts above.
|
|
const unsigned a_lane_off = static_cast<unsigned>(
|
|
(a_row0 + rh8 * 8 + r7) * kK + ((rh16 ^ lswz) << 4));
|
|
const unsigned b_lane_off =
|
|
static_cast<unsigned>((b_row0 + r7) * kK + ((rh8 ^ lswz) << 4));
|
|
// x4-paired B loads (cuBLAS/CUTLASS loop shape): one ldmatrix.x4 feeds
|
|
// the two adjacent nt fragments — 2 x4 instead of 4 x2 per k_seg (12
|
|
// LDSM per k-tile instead of 16). Lane contract: lanes 0-7 address
|
|
// rows n0..n7 chunk c, lanes 8-15 rows n0..n7 chunk c+1, lanes 16-23
|
|
// rows n8..n15 chunk c, lanes 24-31 rows n8..n15 chunk c+1; regs
|
|
// {r0,r1} are the even nt's k-halves, {r2,r3} the odd nt's. The +8-row
|
|
// step never reaches the swizzle source bits for kK <= 64 (kChunks<=4:
|
|
// bits row[2:1]), so lanes 16-31 reuse the same lswz and each pair
|
|
// address is the even-nt base + p*(16*kK). kK=128 swizzles on row[2:0]
|
|
// where +8 flips bits — that config keeps the x2 loads.
|
|
constexpr bool kPairB = kK / 16 <= 4;
|
|
static_assert(!kPairB || kNt % 2 == 0, "B pairing needs even kNt");
|
|
constexpr unsigned kPairStep = 16 * kK; // bytes per nt-pair row step
|
|
const unsigned b4_lane_off = b_lane_off + rh16 * kPairStep / 2;
|
|
|
|
// Prime the pipeline. Each committed group occupies one circular shared
|
|
// memory stage; the loop also handles K dimensions smaller than kStages.
|
|
// Direct loads run synchronously here (back to back with their commit);
|
|
// the steady state below overlaps them with the compute phase.
|
|
#pragma unroll
|
|
for (int stage = 0; stage < kStages; ++stage) {
|
|
if (stage < tile_count) {
|
|
if (fast_cta)
|
|
load_async_fast(stage);
|
|
else
|
|
load_async(stage);
|
|
load_direct(stage);
|
|
astrai::cp_async_commit_group();
|
|
}
|
|
}
|
|
|
|
// Mainloop, compile-time specialized on fast_cta: the fast copy runs
|
|
// predication-free loads; the generic copy keeps full predication.
|
|
// kFastLoop=false instantiates only the generic copy — codegen identical
|
|
// to the pre-peel kernel.
|
|
auto mainloop = [&](auto fastc) {
|
|
constexpr bool kFast = decltype(fastc)::value;
|
|
for (int64_t tile_index = 0; tile_index < tile_count; ++tile_index) {
|
|
const int64_t remaining = tile_count - tile_index - 1;
|
|
|
|
// Keep up to kStages - 1 younger groups in flight while making the
|
|
// oldest group (the current stage) ready for consumption.
|
|
const int keep_groups =
|
|
remaining < kStages - 1 ? static_cast<int>(remaining) : kStages - 1;
|
|
astrai::cp_async_wait_group_dispatch<kStages - 1>(keep_groups);
|
|
// Barrier 1: every thread's cp.async for this stage is complete
|
|
// before any thread reads tiles written by other threads.
|
|
__syncthreads();
|
|
|
|
// Direct chunks for tile i+kStages: issue LDG+PRMT+STS now so the
|
|
// global-load latency hides behind the MMA phase below.
|
|
if (tile_index + kStages < tile_count)
|
|
load_direct(tile_index + kStages);
|
|
|
|
const T8* a_tile = a_base + (size_t)(tile_index % kARing) * kAStageBytes;
|
|
const T8* b_tile = b_base + (size_t)(tile_index % kBRing) * kBStageBytes;
|
|
const unsigned a_addr = __cvta_generic_to_shared(a_tile) + a_lane_off;
|
|
const unsigned b_addr = __cvta_generic_to_shared(b_tile) +
|
|
(kPairB ? b4_lane_off : b_lane_off);
|
|
// Per-k_seg base pair (cuBLAS's scheme): seg s lives at the seg-0
|
|
// base XOR (s<<5) — one LOP3 per extra seg per k-tile, never per
|
|
// fragment. Every LDSM below addresses [base + immediate].
|
|
unsigned a_seg[kSegs], b_seg[kSegs];
|
|
#pragma unroll
|
|
for (int s = 0; s < kSegs; ++s) {
|
|
a_seg[s] = a_addr ^ (unsigned)(s * kSegXor);
|
|
b_seg[s] = b_addr ^ (unsigned)(s * kSegXor);
|
|
}
|
|
|
|
// kNt ldmatrix.x2 (B) + kMt ldmatrix.x4 (A) feed kMt*kNt*2 mma.sync
|
|
// per k_seg — 0.5 load instructions per MMA, versus 4.5 scalar LDS
|
|
// per MMA in the 128x64-tile version (the kernel was LSU-issue-bound
|
|
// there). B fragments double-buffer across k_segs. kPairB folds the
|
|
// two adjacent nt fragments of one pair into a single x4 (see
|
|
// b4_lane_off above): kNt/2 x4 loads, regs {r0,r1}/{r2,r3} feeding
|
|
// the even/odd nt MMAs respectively.
|
|
unsigned b_frag[2][kNt][2];
|
|
unsigned b_frag4[2][kNt / 2][4];
|
|
#pragma unroll
|
|
for (int p = 0; p < kNt / 2; ++p)
|
|
if constexpr (kPairB)
|
|
astrai::ldmatrix_x4_lane(b_frag4[0][p],
|
|
b_seg[0] + p * kPairStep);
|
|
else {
|
|
astrai::ldmatrix_x2_lane(b_frag[0][p * 2],
|
|
b_seg[0] + p * 2 * kNtStep);
|
|
astrai::ldmatrix_x2_lane(b_frag[0][p * 2 + 1],
|
|
b_seg[0] + (p * 2 + 1) * kNtStep);
|
|
}
|
|
#pragma unroll
|
|
for (int k_seg = 0; k_seg < kSegs; ++k_seg) {
|
|
const int bcur = k_seg & 1, bnext = bcur ^ 1;
|
|
if (k_seg + 1 < kSegs) {
|
|
#pragma unroll
|
|
for (int p = 0; p < kNt / 2; ++p)
|
|
if constexpr (kPairB)
|
|
astrai::ldmatrix_x4_lane(
|
|
b_frag4[bnext][p],
|
|
b_seg[k_seg + 1] + p * kPairStep);
|
|
else {
|
|
astrai::ldmatrix_x2_lane(
|
|
b_frag[bnext][p * 2],
|
|
b_seg[k_seg + 1] + p * 2 * kNtStep);
|
|
astrai::ldmatrix_x2_lane(
|
|
b_frag[bnext][p * 2 + 1],
|
|
b_seg[k_seg + 1] + (p * 2 + 1) * kNtStep);
|
|
}
|
|
}
|
|
// Software-pipelined A fragments: the ldmatrix.x4 for row mt+1
|
|
// is issued before the MMAs consuming row mt, so the LDS fixed
|
|
// latency hides behind tensor-pipe work (cuts the `wait` stall,
|
|
// ~2.3 cycles/issue before this). Costs 4 extra registers.
|
|
// (Cross-k_seg prefetch of row 0 was tried and reverted: the
|
|
// register handoff broke ptxas's software pipelining — 171T → 95T
|
|
// at 2048³; the tensor pipe is issue-bound and the seg-start LDS
|
|
// already hides behind the b-fragment issue order.)
|
|
unsigned a_frag[kMt + 1][4];
|
|
astrai::ldmatrix_x4_lane(a_frag[0], a_seg[k_seg]);
|
|
#pragma unroll
|
|
for (int mt = 0; mt < kMt; ++mt) {
|
|
if (mt + 1 < kMt)
|
|
astrai::ldmatrix_x4_lane(a_frag[mt + 1],
|
|
a_seg[k_seg] + (mt + 1) * kMtStep);
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt) {
|
|
const unsigned* bops =
|
|
kPairB ? (b_frag4[bcur][nt >> 1] + (nt & 1) * 2)
|
|
: b_frag[bcur][nt];
|
|
astrai::mma_sync<T8>(acc[nt][mt], a_frag[mt], bops,
|
|
acc[nt][mt]);
|
|
}
|
|
}
|
|
}
|
|
// Barrier 4 (lean-ring only): every thread finished reading this
|
|
// stage's tiles before the prefetch for the (i+kStages)-th tile
|
|
// overwrites them. With the kStages+1 canonic rotation the prefetch
|
|
// targets the slot compute(i-1) released before barrier 1, so the
|
|
// full-ring path skips this barrier entirely — one __syncthreads per
|
|
// k-tile.
|
|
if constexpr (kLeanRing) __syncthreads();
|
|
if (tile_index + kStages < tile_count) {
|
|
if constexpr (kFast)
|
|
load_async_fast(tile_index + kStages);
|
|
else
|
|
load_async(tile_index + kStages);
|
|
astrai::cp_async_commit_group();
|
|
}
|
|
}
|
|
}; // mainloop
|
|
// NOTE: a cross-k-tile fragment pipeline (kAheadFrag — head-load the
|
|
// current tile's tail-seg fragments, tail-preload the next tile's
|
|
// seg-0 behind a tightened wait(kStages-2), mirroring cuBLAS's third
|
|
// SASS mechanism) was implemented and measured here: correct, but
|
|
// neutral-to-negative on L20 (-7% at 512³'s sub-wave grid, noise
|
|
// elsewhere). The shallower effective pipeline (kStages-1 groups in
|
|
// flight) costs what the LDSM spreading saves at these tile counts,
|
|
// and ptxas loses its within-iteration software pipelining across the
|
|
// iteration-boundary register handoff. Removed; see
|
|
// perf/fp8_gemm_optimization.md's reverted-experiments table.
|
|
if constexpr (kFastLoop) {
|
|
if (fast_cta)
|
|
mainloop(std::true_type{});
|
|
else
|
|
mainloop(std::false_type{});
|
|
} else {
|
|
mainloop(std::false_type{});
|
|
}
|
|
|
|
// Direct bf16 epilogue through the operand shared memory: the A/B rings
|
|
// are dead once the mainloop ends, so their space stages the output tile
|
|
// (kBlockM x kBlockN bf16, always <= the ring budget). Threads first
|
|
// scatter their accumulators into the tile (STS.32 of bf16x2 pairs), a
|
|
// barrier makes the tile coherent, then the whole CTA copies it out in
|
|
// fully-coalesced 16B chunks. The direct per-thread stores this replaces
|
|
// hit 8 disjoint 16B segments per warp (rows are n*2 bytes apart), ~50%
|
|
// write efficiency — measurable at 2048+ where the epilogue is ~8% of
|
|
// runtime. The 16B-chunk XOR swizzle (chunk index ^ row) keeps both the
|
|
// scatter and the gather conflict-free: a lane quad's chunk and the 8
|
|
// rows of one gather phase map to distinct 4-bank groups.
|
|
const float output_scale = scale;
|
|
// Fused bias (idea B): added to the fp32 accumulator before the single
|
|
// bf16 rounding — one fewer rounding than the out + bias elementwise
|
|
// pass this replaces, and no extra kernel launch / m*n round-trip. The
|
|
// per-lane loads (2 per nt, kMt-times re-read) are L1 broadcasts; rows
|
|
// past the N edge skip the load (their smem slots never copy out).
|
|
const __nv_bfloat16* bias =
|
|
reinterpret_cast<const __nv_bfloat16*>(p.bias_ptr);
|
|
__nv_bfloat16* tile_out = reinterpret_cast<__nv_bfloat16*>(fp8_gemm_smem);
|
|
constexpr int kRowChunks = kBlockN / 8; // 16B chunks per tile row
|
|
static_assert(kBlockM * kBlockN * 2 <=
|
|
kARing * kBlockM * kK + kBRing * kBlockN * kK,
|
|
"output tile must fit the reclaimed operand smem");
|
|
// Swizzled address of one 16B chunk (row r, chunk c) of the tile.
|
|
auto out_chunk = [&](int r, int c) -> __nv_bfloat16* {
|
|
return tile_out + (size_t)r * kBlockN +
|
|
((c ^ (r & (kRowChunks - 1))) * 8);
|
|
};
|
|
const int local_col0 = warp_n * Traits::kWarpN + thread_in_group * 2;
|
|
const int64_t bias_col0 = (int64_t)block_n * kBlockN;
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt) {
|
|
const int col = local_col0 + nt * 8;
|
|
const int64_t gcol = bias_col0 + col;
|
|
const float b0 =
|
|
bias && gcol < n ? __bfloat162float(bias[gcol]) : 0.0f;
|
|
const float b1 =
|
|
bias && gcol + 1 < n ? __bfloat162float(bias[gcol + 1]) : 0.0f;
|
|
#pragma unroll
|
|
for (int mt = 0; mt < kMt; ++mt) {
|
|
const int r0 = warp_m * Traits::kWarpM + group + mt * 16;
|
|
const float* tile_acc = acc[nt][mt];
|
|
// Two bf16x2 stores per accumulator tile: rows g and g+8 of the
|
|
// m16n8 output, columns tig*2 and tig*2+1 inside one 16B chunk.
|
|
const int off = col & 7; // element offset within the chunk
|
|
*reinterpret_cast<__nv_bfloat162*>(out_chunk(r0, col >> 3) + off) =
|
|
__floats2bfloat162_rn(tile_acc[0] * output_scale + b0,
|
|
tile_acc[1] * output_scale + b1);
|
|
*reinterpret_cast<__nv_bfloat162*>(out_chunk(r0 + 8, col >> 3) +
|
|
off) =
|
|
__floats2bfloat162_rn(tile_acc[2] * output_scale + b0,
|
|
tile_acc[3] * output_scale + b1);
|
|
}
|
|
}
|
|
__syncthreads();
|
|
// Coalesced copy-out: thread -> one 16B chunk; consecutive threads walk
|
|
// a row so each global transaction covers a full 128B line.
|
|
const int64_t row0_global = (int64_t)block_m * kBlockM;
|
|
const int64_t col0_global = (int64_t)block_n * kBlockN;
|
|
constexpr int kTotalChunks = kBlockM * kRowChunks;
|
|
for (int idx = tid; idx < kTotalChunks; idx += kCtaThreads) {
|
|
const int r = idx / kRowChunks;
|
|
const int c = idx % kRowChunks;
|
|
const int64_t row = row0_global + r;
|
|
if (row >= m) break; // rows are consecutive: nothing left in range
|
|
const int64_t col = col0_global + (int64_t)c * 8;
|
|
const uint4 v = *reinterpret_cast<const uint4*>(out_chunk(r, c));
|
|
auto* dst = out_bf16 + row * n + col;
|
|
if (col + 8 <= n && (reinterpret_cast<uintptr_t>(dst) & 15) == 0) {
|
|
if constexpr (kStreamOut) {
|
|
// Evict-first streaming store knob. Measured neutral on
|
|
// L20 squares and -3..4% on rects (the evict-first policy
|
|
// hurts more than the L2 B-tile protection helps at these
|
|
// sizes); kept as a template knob for other SKUs. Default
|
|
// off.
|
|
__stcs(reinterpret_cast<uint4*>(dst), v);
|
|
} else {
|
|
*reinterpret_cast<uint4*>(dst) = v;
|
|
}
|
|
} else {
|
|
// N-tail chunk or an odd-n row base: spill the elements that
|
|
// survive the row edge (and stay aligned).
|
|
const __nv_bfloat16* elems =
|
|
reinterpret_cast<const __nv_bfloat16*>(&v);
|
|
for (int e = 0; e < 8 && col + e < n; ++e) dst[e] = elems[e];
|
|
}
|
|
}
|
|
}
|
|
|
|
// ---------------------------------------------------------------------------
|
|
// Launchers — pure CUDA (no torch), usable from the binding and pure C tests.
|
|
// ---------------------------------------------------------------------------
|
|
|
|
// SM count of the current device (cached per device; benign init race —
|
|
// every writer stores the same value). Host-side only: feeds the
|
|
// device-adaptive dispatch thresholds.
|
|
inline int device_sm_count() {
|
|
static int cached[64] = {};
|
|
int dev = 0;
|
|
cudaGetDevice(&dev);
|
|
if (dev < 0 || dev >= 64) {
|
|
int sms = 0;
|
|
cudaDeviceGetAttribute(&sms, cudaDevAttrMultiProcessorCount, dev);
|
|
return sms > 0 ? sms : 1;
|
|
}
|
|
if (!cached[dev]) {
|
|
int sms = 0;
|
|
cudaDeviceGetAttribute(&sms, cudaDevAttrMultiProcessorCount, dev);
|
|
cached[dev] = sms > 0 ? sms : 1;
|
|
}
|
|
return cached[dev];
|
|
}
|
|
|
|
|
|
// Launch one kernel instantiation with its shared-memory budget: stages live
|
|
// in dynamic smem, so budgets beyond the 48KB static limit opt in once per
|
|
// instantiation via cudaFuncSetAttribute (see AGENTS.md "dynamic shared
|
|
// memory"). Templated on the kernel *value* (auto NTTP) so every
|
|
// instantiation owns its own armed flag — same-signature kernels must not
|
|
// share it (the attribute is per-function).
|
|
template <auto Kernel, typename... Args>
|
|
void launch_with_smem(int smem_bytes, dim3 grid, dim3 block,
|
|
cudaStream_t stream, Args... args) {
|
|
if (smem_bytes > 48 * 1024) {
|
|
static bool armed = false; // per instantiation
|
|
if (!armed) {
|
|
cudaFuncSetAttribute(Kernel,
|
|
cudaFuncAttributeMaxDynamicSharedMemorySize,
|
|
smem_bytes);
|
|
armed = true;
|
|
}
|
|
}
|
|
Kernel<<<grid, block, smem_bytes, stream>>>(args...);
|
|
}
|
|
|
|
// Pre-quantized GEMM tile config: 128x128 CTA (8 warps x 64x32 warp tiles).
|
|
// kK selects the K tile (32 / 64 / 128; larger kK halves the __syncthreads
|
|
// count per K and doubles the MMA work per stage at more smem per stage).
|
|
// Stages is the cp.async pipeline depth (smem = Stages * (BM + BN) * kK
|
|
// bytes for congruous layouts; deep pipelines are dynamic-smem backed, 1
|
|
// CTA/SM past 48KB). GroupRaster defaults to the historically-measured best
|
|
// per LayoutA (grouped for A-crosswise, plain for A-congruous).
|
|
// Crosswise operands always take load_crosswise_direct — the alternative
|
|
// staging+transpose pipeline measured 15-20% slower everywhere probed
|
|
// (contract k 2048..32768, DRAM-streaming B included) and was removed.
|
|
|
|
// Shape-based tile dispatch (grid-searched on the production shapes, see
|
|
// perf/fp8_sweep.cu): small outputs take 64x64 CTAs of 32x32 warps
|
|
// with a lean (kStages-deep) ring: 24KB of smem keeps 4 CTAs resident, and
|
|
// the extra blocks fill the wave quantization gap (512^3: 64 vs 16 CTAs).
|
|
// The large-output path takes the 128x128 CTA (8 warps x 64x32) with the
|
|
// kStages+1 ring — one __syncthreads per k-tile and ~200 TF at scale.
|
|
// The threshold applies to the TOTAL tile count (batch x per-matrix tiles):
|
|
// batched runs keep full per-matrix CTA efficiency once the aggregate grid
|
|
// saturates the device (measured 64x512^3: big 160 vs small 123 TF — a
|
|
// per-matrix-only threshold lost 30%). m <= 64 always takes the small CTA:
|
|
// a 128-row CTA would waste half its MMA work on predicated-off rows.
|
|
//
|
|
// Wave-quantization makes the crossover non-monotonic (92-SM L20, cubes,
|
|
// congruous NT): the 128x128 CTA wins inside one full wave (81 tiles: big
|
|
// +24%) and from ~1.5 waves up (144: +23%, 256: +39%, 2048^3 123->171 TF),
|
|
// but loses inside the quantization dip just past one wave (100 tiles =
|
|
// 1.09 waves: big -8%) where the finer 64x64 grid fills the tail. With the
|
|
// interior fast loop on the big CTA the sub-wave boundary moved down: 63-64
|
|
// tiles already favor it (63-tile rect +8%, 1024^3 +2%) while 49 tiles
|
|
// stays small-CTA territory, so the big band opens at 5/8 wave instead of
|
|
// 3/4.
|
|
inline bool prefer_small_cta(int64_t tiles_128, int64_t m) {
|
|
if (m <= 64) return true;
|
|
const int64_t waves = device_sm_count();
|
|
if (tiles_128 >= waves * 5 / 8 && tiles_128 <= waves) return false;
|
|
return tiles_128 < waves + waves * 2 / 5;
|
|
}
|
|
|
|
template <FP8Format Fmt, typename LayoutA = RowMajor,
|
|
typename LayoutB = RowMajor, int kK = 64, int Stages = 2,
|
|
int GroupRaster = (std::is_same_v<LayoutA, ColMajor> ||
|
|
std::is_same_v<LayoutB, ColMajor>)
|
|
? 8
|
|
: 0>
|
|
void launch_fp8_gemm(const FP8Params& p, cudaStream_t stream) {
|
|
// m <= 64 and small total outputs share the 64x64 small CTA (with the
|
|
// predication-free interior loop); the predicate counts batch x
|
|
// per-matrix tiles (see prefer_small_cta).
|
|
const int64_t tiles_128 =
|
|
(int64_t)p.batch * ((p.m + 127) / 128) * ((p.n + 127) / 128);
|
|
if (prefer_small_cta(tiles_128, p.m)) {
|
|
dim3 grid((p.n + 63) / 64, (p.m + 63) / 64, p.batch);
|
|
// Full-ring small CTAs — ONE __syncthreads per k-tile, cuBLAS's
|
|
// barrier structure (the lean ring traded a second barrier for a
|
|
// 4th resident CTA and measured slower: the barrier costs more
|
|
// than the residency buys, e.g. 1280³ +5..9%). Two depths by grid
|
|
// shape: the 24KB 3-slot s2 variant keeps 4 CTAs/SM while the
|
|
// whole grid stays resident (<= one 3-CTA wave); past that the
|
|
// 32KB s3 variant's deeper cp.async pipeline wins on multi-wave
|
|
// grids (measured 1280³: 107T vs 98T; sub-wave grids tie within
|
|
// +-1%). kFastLoop stays on: the predication-free interior load
|
|
// is where the small CTA's issue budget goes.
|
|
const int64_t tiles_64 =
|
|
(int64_t)p.batch * ((p.m + 63) / 64) * ((p.n + 63) / 64);
|
|
if (tiles_64 <= (int64_t)device_sm_count() * 3) {
|
|
using Traits = Fp8GemmTraits<Fmt, 64, 64, kK, 2, 32, 32>;
|
|
launch_with_smem<
|
|
fp8_gemm_kernel<Traits, LayoutA, LayoutB, GroupRaster, false,
|
|
false, true>>(
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, false>::kBytes, grid,
|
|
dim3(Traits::kCtaThreads), stream, p);
|
|
} else {
|
|
using Traits = Fp8GemmTraits<Fmt, 64, 64, kK, 3, 32, 32>;
|
|
launch_with_smem<
|
|
fp8_gemm_kernel<Traits, LayoutA, LayoutB, GroupRaster, false,
|
|
false, true>>(
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, false>::kBytes, grid,
|
|
dim3(Traits::kCtaThreads), stream, p);
|
|
}
|
|
return;
|
|
}
|
|
using Traits = Fp8GemmTraits<Fmt, 128, 128, kK, Stages>;
|
|
dim3 grid((p.n + 127) / 128, (p.m + 127) / 128, p.batch);
|
|
// Interior-loop specialization on the big CTA as well: with the base-pair
|
|
// fragment addressing the doubled mainloop no longer spills, and the
|
|
// predication-free loads win across the band (measured, L20: 1024^3
|
|
// 98->103T, 2048^3 172->177T, 8192^3 201->205T, 896x1280 124->135T; the
|
|
// pre-base-pair attempt regressed ~3% at 131 regs). Only congruous
|
|
// layouts can enter fast_cta, so crosswise (TN) instantiations keep the
|
|
// single generic body — no dead second loop in their I-cache.
|
|
constexpr bool kBigFast = !std::is_same_v<LayoutA, ColMajor> &&
|
|
!std::is_same_v<LayoutB, RowMajor>;
|
|
// Single-wave grids (tiles <= SM count) take one stage deeper: with no
|
|
// second wave to overlap the drain, latency hiding comes only from the
|
|
// pipeline (measured, L20, in-wave band: 1024^3 +1.5%, 1152^3 +1.2%,
|
|
// K=4096 rects +2%); multi-wave grids flip back — the shorter prologue
|
|
// wins once retiring CTAs overlap (4096^3: s2 196T vs s3 175T).
|
|
if (tiles_128 <= (int64_t)device_sm_count()) {
|
|
using TraitsS3 = Fp8GemmTraits<Fmt, 128, 128, kK, Stages + 1>;
|
|
launch_with_smem<
|
|
fp8_gemm_kernel<TraitsS3, LayoutA, LayoutB, GroupRaster, false,
|
|
false, kBigFast>>(
|
|
Fp8GemmSmem<TraitsS3, LayoutA, LayoutB, false>::kBytes, grid,
|
|
dim3(TraitsS3::kCtaThreads), stream, p);
|
|
return;
|
|
}
|
|
launch_with_smem<
|
|
fp8_gemm_kernel<Traits, LayoutA, LayoutB, GroupRaster, false, false,
|
|
kBigFast>>(
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, false>::kBytes, grid,
|
|
dim3(Traits::kCtaThreads), stream, p);
|
|
}
|
|
|
|
} // namespace fp8
|
|
} // namespace astrai
|