ViperEkura
4d6a244093
- mm_fp8 accepts 3D operands through the same signature: grid.z slices by batch strides, size-1 batches broadcast (stride 0), inner .t() views fold into the layout tag at zero copy - fix _LinearFp8 backward crash on 3D [B,L,d] training inputs (flatten before mm_fp8, reduce grad_b over leading dims) - expose kRasterGroup/kStreamOut as template knobs; drop the 64x128 mid CTA and staged crosswise-B path from dispatch (direct wins everywhere re-measured, including DRAM-streamed B) - dispatch thresholds grounded in fresh sweeps: m<=64 -> 64x64 CTA (+27% at 64x8192x2048), small-CTA crossover at SM*14/3 total tiles (+13% at 96 tiles), threshold counts batch x per-matrix tiles (+31% at 64x512^3 bmm, +25% at 8x1024x2048) - remove scripts/tools/bench_fp8_gemm.py (superseded by csrc/tests/fp8_sweep.cu for kernel-level tuning) Benchmark: NVIDIA L20, E4M3, NT pre-quantized, median of 100-200 iters - 64x8192x2048: 29.1 -> 22.8 us (94 TF/s) - 1024x1536x2048: 67.4 -> 59.6 us (108 TF/s) - bmm 64x512^3: 139.8 -> 106.7 us; bmm 8x1024x2048: 186 TF/s - regression-free: 4096^3 192 TF/s, 8192^3 200 TF/s, 512^3 unchanged
895 lines
46 KiB
Plaintext
895 lines
46 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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constexpr int kWarps = 8; // 128x128 CTA = 8 warps
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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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// Map the FP8Format enum to the CUDA fp8 element type consumed by mma_sync.
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template <FP8Format Fmt>
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struct fp8_input {
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using type = __nv_fp8_e4m3;
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};
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template <>
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struct fp8_input<FP8Format::E5M2> {
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using type = __nv_fp8_e5m2;
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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 fp8_input<Fmt>::type. Accumulates in-place: callers
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// pass the same accumulator array as both `d` and `c`.
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// warp_reduce_sum / group_reduce_sum (GEMM) live in common/reduce.cuh; the
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// cp.async pipeline primitives (predicated 16-byte copy, commit_group,
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// wait_group + runtime dispatch) 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 stage_crosswise_tile + transpose_crosswise_tile 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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// ---------------------------------------------------------------------------
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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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// Swizzled 16B-chunk address (tile_at's layout) as a raw shared-memory
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// pointer for ldmatrix. Valid for kK in {32, 64, 128} (the swizzle itself
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// lives only in tile_at; this wrapper just converts the element address).
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template <typename T8, int kK>
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__device__ __forceinline__ unsigned frag_addr(const T8* tile, int row, int chunk) {
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static_assert(kK == 32 || kK == 64 || kK == 128,
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"fragment swizzle offsets assume kK in {32, 64, 128}");
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return __cvta_generic_to_shared(tile_at<kK>(tile, row, chunk << 4));
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}
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// Crosswise operands (stored [contract][rows], rows-contiguous) cannot be
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// cp.async'd into the canonical [rows][contract] tile — a 16B global run
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// holds one contract byte for each of 16 rows. They stage K-major instead
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// (byte (p, r) at p*RowsTile + r), where the very same runs land contiguously
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// and cp.async applies unchanged; a per-tile smem->smem transpose (below)
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// then produces the canonical swizzled tile the MMA fragments read. This
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// keeps the whole global→shared path asynchronous — the synchronous
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// LDG+byte-scatter staging this replaces left the kernel long-scoreboard
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// bound (ncu: 4.6 stalled loads per issue vs 0.4 on the congruous path).
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template <typename T8, int K, int RowsTile, int kThreads>
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__device__ __forceinline__ void
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stage_crosswise_tile(T8* staging, 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 kRuns = K * RowsTile / 16; // 16B runs per tile
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// r0 is a multiple of 16 and p*ld keeps 16B alignment whenever ld has it,
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// so one uniform verdict covers every run.
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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 run = tid; run < kRuns; run += kThreads) {
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const int pl = run % K; // local contract byte (column of the run)
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const int rg = run / K; // 16-row group
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const int64_t r0 = block_row + (int64_t)rg * 16;
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T8* dst = staging + pl * RowsTile + rg * 16;
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if (run_aligned && r0 + 15 < rows && k_base + pl < contract)
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astrai::cp_async_16(dst, operand + (k_base + pl) * ld + r0, true);
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else {
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// Row tail, contract tail or misaligned base: predicated fill.
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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 = r0 + i;
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dst[i] = r < rows && k_base + pl < contract
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? operand[(k_base + pl) * ld + r]
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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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// 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. Used for crosswise operands whose global data is
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// typically L2-resident (the A side of dW): the staging detour's extra
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// shared-memory round trip costs more than the latency it hides there,
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// while crosswise B operands (DRAM-streamed weights of dX) take the
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// asynchronous stage_crosswise_tile path 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_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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// K-major staging -> canonical [rows][kK] swizzled tile, one chunk at a time.
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// Each chunk (indexed within a k_seg region of `quads_per_seg` quads) covers
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// 4 consecutive contract bytes x 16 rows: four LDS.128 grab the staging runs,
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// PRMT byte selects transpose them in registers, and sixteen STS.32 land the
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// row quads through tile_at's swizzle — 4x fewer store instructions than a
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// byte-granular scatter. Chunk-at-a-time lets the caller pool work across
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// operands; the region restriction lets the main loop overlap one region's
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// transpose with another region's MMAs (a whole-tile serial transpose put
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// the crosswise GEMMs at 25% tensor utilization).
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template <typename T8, int K, int RowsTile>
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__device__ __forceinline__ void
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transpose_crosswise_region(T8* tile, const T8* staging, int idx, int quad0) {
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constexpr int kGroups = RowsTile / 16;
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const int quad = quad0 + idx / kGroups;
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const int rg = idx % kGroups;
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// The four runs sit RowsTile bytes apart (one per contract byte of the
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// quad); each run is 16 contiguous staging bytes = 16 rows.
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const char* run0 = reinterpret_cast<const char*>(
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staging + quad * 4 * RowsTile + rg * 16);
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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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v[s] = *reinterpret_cast<const uint4*>(run0 + s * RowsTile);
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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 lives in
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// 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, quad * 4)) =
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__byte_perm(w01, w23, 0x5410u);
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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. A staged-crosswise B always costs kStages K-major
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// staging buffers + one canonical buffer.
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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, bool StagedB,
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bool LeanRing = false>
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struct Fp8GemmSmem {
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// Crosswise = the stage-load's view: A's tag directly, B's transposed.
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// A-crosswise always loads direct (L2-typical activations); B-crosswise
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// stages only when its contract dim is long enough to stream DRAM.
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static constexpr bool kCrossA = std::is_same_v<LayoutA, ColMajor>;
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static constexpr bool kCrossB = std::is_same_v<LayoutB, RowMajor>;
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static constexpr bool kBStagePath = kCrossB && StagedB;
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static constexpr bool kDirectA = kCrossA;
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static constexpr bool kDirectB = kCrossB && !kBStagePath;
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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 =
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kBStagePath ? Traits::kStages + 1
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: (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 kBStaged = true, bool kLeanRing = false, bool kStreamOut = false>
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__global__ void __launch_bounds__(Traits::kCtaThreads,
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Fp8GemmSmem<Traits, LayoutA, LayoutB,
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kBStaged, 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;
|
|
constexpr int kCtaThreads = Traits::kCtaThreads;
|
|
constexpr bool kCrossA = Fp8GemmSmem<Traits, LayoutA, LayoutB, kBStaged>::kCrossA;
|
|
constexpr bool kCrossB = Fp8GemmSmem<Traits, LayoutA, LayoutB, kBStaged>::kCrossB;
|
|
constexpr bool kBStagePath =
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, kBStaged>::kBStagePath;
|
|
constexpr bool kDirectA = Fp8GemmSmem<Traits, LayoutA, LayoutB, kBStaged>::kDirectA;
|
|
constexpr bool kDirectB = Fp8GemmSmem<Traits, LayoutA, LayoutB, kBStaged>::kDirectB;
|
|
static_assert(kStages >= 1 && kStages <= 8,
|
|
"FP8 GEMM stages must be in [1, 8]");
|
|
// Tiles are flat [rows * kK] with a 16B-chunk XOR swizzle (tile_at):
|
|
// ldmatrix reads whole 16B chunks through the same mapping the staging
|
|
// writes, and the swizzle removes the bank conflict the unswizzled
|
|
// 8-word row stride caused (see tile_at). The stages live in dynamic
|
|
// shared memory so deep pipelines (kStages * (kBlockM + kBlockN) * kK >
|
|
// 48KB static limit) opt in via cudaFuncSetAttribute in the launcher.
|
|
extern __shared__ __align__(16) char fp8_gemm_smem[];
|
|
// Per operand: congruous = kStages+1 rotating canonical buffers — the
|
|
// load for tile i+kStages targets slot (i-1)%(kStages+1), which compute
|
|
// finished reading before this iteration's barrier 1, so NO post-compute
|
|
// barrier is needed on the pure-congruous path (one __syncthreads per
|
|
// k-tile, the classic multistage rotation); direct-crosswise rotates the
|
|
// same kStages+1 ring for the same reason; staged-crosswise (B) keeps
|
|
// kStages K-major staging buffers (filled by cp.async) plus ONE canonical
|
|
// buffer the per-tile transpose rewrites (its barrier structure keeps
|
|
// barrier 4).
|
|
constexpr int kAStageBytes = kBlockM * kK;
|
|
constexpr int kBStageBytes = kBlockN * kK;
|
|
// Direct-crosswise operands always rotate kStages+1 buffers: their
|
|
// prefetch issues right after barrier 1 (targeting the slot compute(i-1)
|
|
// released), so a kStages-deep lean ring would race the in-flight MMA
|
|
// reads. The lean ring applies only to congruous operands, whose cp.async
|
|
// prefetch sits behind the restored barrier 4.
|
|
constexpr int kARing = kDirectA ? kStages + 1 : kStages + !kLeanRing;
|
|
constexpr int kBRing = kDirectB ? kStages + 1 : kStages + !kLeanRing;
|
|
constexpr int kStB = kStages; // B staging ring size
|
|
T8* const a_base = reinterpret_cast<T8*>(fp8_gemm_smem);
|
|
T8* const b_base =
|
|
reinterpret_cast<T8*>(fp8_gemm_smem + kARing * kAStageBytes);
|
|
T8* const b_canon = b_base + kStB * kBStageBytes; // staged B only
|
|
|
|
// Batch slice (grid.z): broadcast operands carry a 0 stride, so the
|
|
// same pointer serves every batch.
|
|
const auto* a = reinterpret_cast<const T8*>(p.a_ptr) +
|
|
(int64_t)blockIdx.z * p.a_batch_stride;
|
|
const auto* b = reinterpret_cast<const T8*>(p.b_ptr) +
|
|
(int64_t)blockIdx.z * p.b_batch_stride;
|
|
auto* out_bf16 = reinterpret_cast<__nv_bfloat16*>(p.out_ptr) +
|
|
(int64_t)blockIdx.z * p.out_batch_stride;
|
|
const int64_t m = p.m, n = p.n, k = p.k;
|
|
const int64_t a_ld = p.a_ld, b_ld = p.b_ld;
|
|
|
|
const int tid = threadIdx.x;
|
|
const int warp = tid >> 5;
|
|
const int lane = tid & 31;
|
|
const int group = lane >> 2;
|
|
const int thread_in_group = lane & 3;
|
|
// Tile scheduler: the linear CTA id maps to (block_m, block_n) in
|
|
// grouped (L2-friendly, CUTLASS-style) or plain raster order — the
|
|
// grouped order makes consecutive CTAs cover a group of kRasterGroup
|
|
// M-tiles before advancing along N, so all CTAs of one group share the
|
|
// same B column stripe and B tiles stay hot in L2 across the wave (the
|
|
// plain N-fastest order makes each wave touch every B tile instead;
|
|
// kRasterGroup=0 selects plain, the measured best for dX's crosswise-B
|
|
// layouts where grouping measured neutral).
|
|
// Persistent schedules (static round-robin and an atomic ticket
|
|
// dispenser, grid capped at the resident CTAs) were both measured and
|
|
// rejected on L20: the stride desynchronizes the in-flight window
|
|
// (-4..-8%), and the ticket variant recovers the L2 locality but lands
|
|
// within noise of plain waves (its loop-head barrier costs what the
|
|
// CTA-restart overlap saves). Keep the classic retiring-wave launch.
|
|
int block_m, block_n;
|
|
if constexpr (kRasterGroup > 0) {
|
|
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
|
|
const int warp_m = warp / Traits::kWarpsN;
|
|
const int warp_n = warp % Traits::kWarpsN;
|
|
const int64_t row_base =
|
|
(int64_t)block_m * kBlockM + warp_m * Traits::kWarpM + group;
|
|
const int64_t output_col = (int64_t)block_n * kBlockN +
|
|
warp_n * Traits::kWarpN +
|
|
thread_in_group * 2;
|
|
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
|
|
// cp.async into K-major staging (zero transformation) and get a per-tile
|
|
// smem->smem transpose below.
|
|
// Asynchronous loads for tile `tile`: congruous operands cp.async into
|
|
// their canonical rings, a staged B cp.asyncs into its K-major staging
|
|
// ring. 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 (kBStagePath)
|
|
stage_crosswise_tile<T8, kK, kBlockN, kCtaThreads>(
|
|
b_base + (tile % kStB) * kBStageBytes, b, n, k, b_ld, tid,
|
|
k_base, (int64_t)block_n * kBlockN);
|
|
if constexpr (!kDirectB && !kBStagePath)
|
|
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);
|
|
};
|
|
// 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);
|
|
};
|
|
// smem->smem transpose of one k_seg region (kSegQuads contract quads) of
|
|
// this tile's staged-crosswise B into its single canonical buffer.
|
|
auto transpose_tile = [&](int tile, int seg) {
|
|
if constexpr (!kBStagePath) return;
|
|
constexpr int kSegQuads = kK / 4 / (kK / kMmaK); // quads per k_seg
|
|
constexpr int kBRegion = kSegQuads * (kBlockN / 16);
|
|
const T8* b_stg = b_base + (tile % kStB) * kBStageBytes;
|
|
for (int idx = tid; idx < kBRegion; idx += kCtaThreads)
|
|
transpose_crosswise_region<T8, kK, kBlockN>(b_canon, b_stg, idx,
|
|
seg * kSegQuads);
|
|
};
|
|
|
|
const int64_t tile_count = (k + kK - 1) / kK;
|
|
|
|
// Per-lane ldmatrix row/chunk selectors for common/mma.cuh's
|
|
// ldmatrix_*_lane (the fragment tiles are XOR-swizzled per 16B chunk, so
|
|
// each lane computes its own row/chunk address). Layout contract for fp8
|
|
// m16n8k32 (values packed two-per-b16 slot, K-contiguous rows):
|
|
// x4 (A fragment): lane i points at tile row (i>>3 & 1)*8 + (i&7) of
|
|
// chunk (k_seg*2 + (i>>4)); reg j = matrix j = [row g][tig*4..+3] in
|
|
// the order (rows 0-7 c, rows 8-15 c, rows 0-7 c+1, rows 8-15 c+1) —
|
|
// exactly the mma.sync A operand layout.
|
|
// x2 (B fragment): lane i points at tile row (i&7) of chunk
|
|
// (k_seg*2 + ((i>>3) & 1)); reg j = [row(n) g][tig*4..+3] chunk c/c+1
|
|
// — exactly the mma.sync B operand layout (col operand, K-contiguous).
|
|
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)
|
|
|
|
// Precomputed per-lane fragment offsets (stage-relative): the XOR
|
|
// swizzle inside tile_at depends only on (row, chunk) — never on the
|
|
// ring slot or tile_index — so every lane's ldmatrix address is its
|
|
// stage base plus one of these fixed offsets. Building the table once,
|
|
// outside the mainloop, removes the per-k_seg swizzle arithmetic
|
|
// (IMAD/LOP3 chains) from the innermost loop; the SASS compute window
|
|
// was ~36% integer address math before this.
|
|
constexpr int kSegs = kK / kMmaK;
|
|
unsigned a_off[kSegs][kMt]; // stage-relative byte offsets
|
|
unsigned b_off[kSegs][kNt];
|
|
{
|
|
// The probe addresses are converted and immediately rebased to the
|
|
// stage origin, so the table holds pure offsets to add to any ring
|
|
// slot's converted base (double-adding the base was the bug here).
|
|
const unsigned a0 = __cvta_generic_to_shared(a_base);
|
|
#pragma unroll
|
|
for (int s = 0; s < kSegs; ++s) {
|
|
#pragma unroll
|
|
for (int mt = 0; mt < kMt; ++mt)
|
|
a_off[s][mt] =
|
|
__cvta_generic_to_shared(
|
|
tile_at<kK>(a_base, a_row0 + mt * 16 + rh8 * 8 + r7,
|
|
(s * 2 + rh16) * 16)) -
|
|
a0;
|
|
}
|
|
const T8* b_probe = kBStagePath ? b_canon : b_base;
|
|
const unsigned b0 = __cvta_generic_to_shared(b_probe);
|
|
#pragma unroll
|
|
for (int s = 0; s < kSegs; ++s) {
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt)
|
|
b_off[s][nt] =
|
|
__cvta_generic_to_shared(
|
|
tile_at<kK>(b_probe, b_row0 + nt * 8 + r7,
|
|
(s * 2 + rh8) * 16)) -
|
|
b0;
|
|
}
|
|
}
|
|
|
|
// 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) {
|
|
load_async(stage);
|
|
load_direct(stage);
|
|
astrai::cp_async_commit_group();
|
|
}
|
|
}
|
|
|
|
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);
|
|
|
|
// Staged-crosswise B: produce the canonical tile one k_seg region at
|
|
// a time so each region's transpose overlaps the previous region's
|
|
// MMA sequence (the transposes are pure shared-memory traffic — B's
|
|
// global path stayed fully asynchronous above).
|
|
if constexpr (kBStagePath) {
|
|
transpose_tile(tile_index, 0);
|
|
// Barrier 2: region 0 visible to every thread before its
|
|
// fragment loads. (Compiled out for congruous/direct layouts.)
|
|
__syncthreads();
|
|
}
|
|
|
|
const T8* a_tile = a_base + (size_t)(tile_index % kARing) * kAStageBytes;
|
|
const T8* b_tile = kBStagePath
|
|
? b_canon
|
|
: b_base + (size_t)(tile_index % kBRing) * kBStageBytes;
|
|
const unsigned a_base_addr = __cvta_generic_to_shared(a_tile);
|
|
const unsigned b_base_addr = __cvta_generic_to_shared(b_tile);
|
|
|
|
// 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 while B is
|
|
// congruous (no region writes in flight); a crosswise B reloads per
|
|
// k_seg after the region's transpose became visible.
|
|
unsigned b_frag[2][kNt][2];
|
|
if constexpr (!kBStagePath) {
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt)
|
|
astrai::ldmatrix_x2_lane(b_frag[0][nt],
|
|
b_base_addr + b_off[0][nt]);
|
|
}
|
|
#pragma unroll
|
|
for (int k_seg = 0; k_seg < kSegs; ++k_seg) {
|
|
const int bcur = k_seg & 1, bnext = bcur ^ 1;
|
|
if constexpr (kBStagePath) {
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt)
|
|
astrai::ldmatrix_x2_lane(
|
|
b_frag[bcur][nt], b_base_addr + b_off[k_seg][nt]);
|
|
} else if (k_seg + 1 < kSegs) {
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt)
|
|
astrai::ldmatrix_x2_lane(
|
|
b_frag[bnext][nt], b_base_addr + b_off[k_seg + 1][nt]);
|
|
}
|
|
// Region k_seg+1's transpose overlaps this region's MMA work
|
|
// (disjoint canonical regions, no race).
|
|
if constexpr (kBStagePath) {
|
|
if (k_seg + 1 < kSegs)
|
|
transpose_tile(tile_index, k_seg + 1);
|
|
}
|
|
// 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_base_addr + a_off[k_seg][0]);
|
|
#pragma unroll
|
|
for (int mt = 0; mt < kMt; ++mt) {
|
|
if (mt + 1 < kMt)
|
|
astrai::ldmatrix_x4_lane(
|
|
a_frag[mt + 1], a_base_addr + a_off[k_seg][mt + 1]);
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt)
|
|
astrai::mma_sync<T8>(acc[nt][mt], a_frag[mt],
|
|
b_frag[bcur][nt], acc[nt][mt]);
|
|
}
|
|
// Barrier 3: region k_seg+1's transposes complete and become
|
|
// visible before the next k_seg reads them.
|
|
if constexpr (kBStagePath) {
|
|
if (k_seg + 1 < kSegs) __syncthreads();
|
|
}
|
|
}
|
|
// Barrier 4 (staged-B / lean-ring only): every thread finished
|
|
// reading this stage's tiles before the prefetch for the
|
|
// (i+kStages)-th tile overwrites them (and the next iteration's
|
|
// transposes rewrite the canonical buffer). With the kStages+1
|
|
// canonic rotation the prefetch targets the slot compute(i-1)
|
|
// released before barrier 1, so the pure-congruous path skips this
|
|
// barrier entirely — one __syncthreads per k-tile.
|
|
if constexpr (kBStagePath || kLeanRing) __syncthreads();
|
|
if (tile_index + kStages < tile_count) {
|
|
load_async(tile_index + kStages);
|
|
astrai::cp_async_commit_group();
|
|
}
|
|
}
|
|
|
|
// 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;
|
|
__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;
|
|
#pragma unroll
|
|
for (int nt = 0; nt < kNt; ++nt) {
|
|
const int col = local_col0 + nt * 8;
|
|
#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,
|
|
tile_acc[1] * output_scale);
|
|
*reinterpret_cast<__nv_bfloat162*>(out_chunk(r0 + 8, col >> 3) +
|
|
off) =
|
|
__floats2bfloat162_rn(tile_acc[2] * output_scale,
|
|
tile_acc[3] * output_scale);
|
|
}
|
|
}
|
|
__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). m <= 64
|
|
// dispatches to the 64x128 CTA — a 128-row CTA would waste half its MMA work
|
|
// on predicated-off rows.
|
|
// Crosswise-B staging+transpose vs the synchronous direct load: measured on
|
|
// the current kernel generation, direct wins everywhere probed — contract k
|
|
// 2048..32768 including B operands (128/256MB) that stream from DRAM past L2
|
|
// (direct 171-181 TF vs staged 140-163 TF; the staging round trip costs more
|
|
// shared-memory traffic than the latency it hides). The old "stage past k=
|
|
// 8192" rule reflected a pre-direct-path kernel; staging is now disabled.
|
|
// The staged kernel template remains for csrc/tests/fp8_sweep.cu A/B runs.
|
|
constexpr int64_t kCrossStageMinK = (int64_t)1 << 62; // unreachable: never stage
|
|
|
|
// Shape-based tile dispatch (grid-searched on the production shapes, see
|
|
// csrc/tests/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.
|
|
// Crossover (congruous NT, k=2048): 96 tiles small +14%, 112 tie, 135 big
|
|
// +16% — threshold at ~2.3 waves of the resident (2/SM) 128x128 CTAs.
|
|
// 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.
|
|
inline int64_t small_shape_max_tiles() {
|
|
return (int64_t)device_sm_count() * 14 / 3; // 112 tiles on a 24-SM part
|
|
}
|
|
|
|
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) {
|
|
// Staging is disabled (see kCrossStageMinK); the flag stays so the
|
|
// staged template instantiations below keep compiling for the sweep.
|
|
const bool b_staged = false;
|
|
// m <= 64 and small total outputs share the 64x64 small CTA; the
|
|
// threshold counts batch x per-matrix tiles (see small_shape_max_tiles).
|
|
const int64_t tiles_128 =
|
|
(int64_t)p.batch * ((p.m + 127) / 128) * ((p.n + 127) / 128);
|
|
if (p.m <= 64 || tiles_128 < small_shape_max_tiles()) {
|
|
using Traits = Fp8GemmTraits<Fmt, 64, 64, kK, 3, 32, 32>;
|
|
dim3 grid((p.n + 63) / 64, (p.m + 63) / 64, p.batch);
|
|
if (b_staged)
|
|
launch_with_smem<fp8_gemm_kernel<Traits, LayoutA, LayoutB,
|
|
GroupRaster, true, true>>(
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, true, true>::kBytes,
|
|
grid, dim3(Traits::kCtaThreads), stream, p);
|
|
else
|
|
launch_with_smem<fp8_gemm_kernel<Traits, LayoutA, LayoutB,
|
|
GroupRaster, false, true>>(
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, false, true>::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);
|
|
if (b_staged)
|
|
launch_with_smem<fp8_gemm_kernel<Traits, LayoutA, LayoutB,
|
|
GroupRaster, true, false>>(
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, true, false>::kBytes, grid,
|
|
dim3(Traits::kCtaThreads), stream, p);
|
|
else
|
|
launch_with_smem<fp8_gemm_kernel<Traits, LayoutA, LayoutB,
|
|
GroupRaster, false, false>>(
|
|
Fp8GemmSmem<Traits, LayoutA, LayoutB, false, false>::kBytes, grid,
|
|
dim3(Traits::kCtaThreads), stream, p);
|
|
}
|
|
|
|
} // namespace fp8
|
|
} // namespace astrai
|