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AstrAI/csrc/tests/attn_decode_test.cu

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/*
Pure-C test:
nvcc -I csrc -arch=sm_89 -O3 \
--use_fast_math --ptxas-options=-O3 --extra-device-vectorization \
csrc/tests/attn_decode_test.cu -o test && ./test
*/
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <sys/time.h>
#include "../kernels/attn_decode_split_kv.cuh"
#ifndef ASTRAI_NO_MMA
#include "../kernels/attn_decode_split_kv_mma.cuh"
#endif
static double now_ms() {
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec * 1000.0 + tv.tv_usec / 1000.0;
}
// Split-K scratch (torch-free): the production launcher allocates these from
// torch; here we pass pre-allocated device buffers so the bench loop doesn't
// pay a cudaMalloc per iteration. Size for the maximum split count (32).
struct DecodeScratch {
float* o_part = nullptr;
float* ml_part = nullptr;
};
static int decode_num_splits(const AttentionParams& p, int tiles_total) {
int sm_count = 0;
cudaDeviceGetAttribute(&sm_count, cudaDevAttrMultiProcessorCount, 0);
int base_blocks = p.kv_head * p.batch;
int desired = 2 * (sm_count > 0 ? sm_count : 64);
int n = (desired + base_blocks - 1) / base_blocks;
int max_by_work = tiles_total / 8;
return max(1, min(min(min(n, tiles_total), 32), max_by_work));
}
// Launch the production decode path (tensor-core head-packing MMA on sm_80+,
// scalar fallback otherwise), mirroring dispatch_decode() in attn_decode.cu.
#ifndef ASTRAI_NO_MMA
static bool decode_use_mma(const AttentionParams& p) {
int G = p.q_head / p.kv_head;
return !p.use_mask && G > 1 && G <= 16;
}
template <int HEAD_DIM, int BC>
static void launch_mma_decode(AttentionParams& p, DecodeScratch& sc) {
int tiles_total = (p.kv_len + BC - 1) / BC;
p.num_splits = decode_num_splits(p, tiles_total);
p.o_part = sc.o_part;
p.ml_part = sc.ml_part;
attn_decode_split_kv_mma_kernel<HEAD_DIM, BC>
<<<dim3(p.kv_head, p.batch, p.num_splits), 32>>>(p);
attn_decode_combine_kernel<<<p.batch * p.q_head, p.head_dim>>>(p);
}
#endif
static void launch_scalar_decode(AttentionParams& p, DecodeScratch& sc) {
int gs = p.q_head / p.kv_head;
int chunks_total = (p.kv_len + DC_CHUNK - 1) / DC_CHUNK;
p.num_splits = decode_num_splits(p, chunks_total);
p.o_part = sc.o_part;
p.ml_part = sc.ml_part;
size_t smem = DC_CHUNK * p.head_dim * sizeof(bf16);
attn_decode_split_kv_kernel<<<dim3(p.batch * p.kv_head, 1, p.num_splits), dim3(32, gs), smem>>>(p);
attn_decode_combine_kernel<<<p.batch * p.q_head, p.head_dim>>>(p);
}
template <int HEAD_DIM>
static void dispatch_decode_t(AttentionParams& p, DecodeScratch& sc) {
#ifndef ASTRAI_NO_MMA
if (decode_use_mma(p)) { launch_mma_decode<HEAD_DIM, 32>(p, sc); return; }
#endif
launch_scalar_decode(p, sc);
}
static void dispatch_decode(AttentionParams& p, DecodeScratch& sc) {
switch (p.head_dim) {
case 32: dispatch_decode_t<32>(p, sc); break;
case 64: dispatch_decode_t<64>(p, sc); break;
case 128: dispatch_decode_t<128>(p, sc); break;
case 256: dispatch_decode_t<256>(p, sc); break;
default: printf("bench: unsupported D=%d\n", p.head_dim);
}
}
static void cpu_decode(const float* Q, const float* K, const float* V,
const bool* mask, float* O,
int B, int Hq, int Hk, int seq_len, int D) {
float scale = 1.0f / sqrtf((float)D);
int n_rep = Hq / Hk;
for (int b = 0; b < B; b++) {
for (int h = 0; h < Hq; h++) {
int kv_h = h / n_rep;
float mv = -INFINITY, sv = 0.0f;
float accum[256] = {0};
for (int s = 0; s < seq_len; s++) {
if (!mask[b * seq_len + s]) continue;
float dot = 0.0f;
for (int d = 0; d < D; d++)
dot += Q[((b * Hq + h) * 1 + 0) * D + d]
* K[((b * Hk + kv_h) * seq_len + s) * D + d];
dot *= scale;
float nm = fmaxf(mv, dot);
float al = expf(mv - nm);
float be = expf(dot - nm);
sv = sv * al + be;
for (int d = 0; d < D; d++)
accum[d] = accum[d] * al
+ V[((b * Hk + kv_h) * seq_len + s) * D + d] * be;
mv = nm;
}
float inv = 1.0f / sv;
for (int d = 0; d < D; d++)
O[((b * Hq + h) * 1 + 0) * D + d] = accum[d] * inv;
}
}
}
static bf16 f2bf(float x) { return __float2bfloat16(x); }
static float bf2f(bf16 x) { return __bfloat162float(x); }
static float randf() { return (float)rand() / (float)RAND_MAX - 0.5f; }
// Warmed-up, CUDA-event timed sweep over the production decode MMA path.
// Decode (q_len==1) is memory-bound: the two matmuls are GEMV-shaped, so we
// report both effective K/V read bandwidth and the (small) attention FLOP/s.
// FLOP/s = 2 matmuls (q@K^T, P@V), each 2*B*Hq*kv*D flops.
// Bytes = K + V read = 2 * B*Hk*kv*D * sizeof(bf16).
static void bench() {
const int cfgs[][5] = {
{1, 32, 4, 512, 128}, // B,Hq,Hk,seq,D
{1, 32, 4, 1024, 128},
{1, 32, 4, 2048, 128},
{1, 32, 4, 4096, 128},
{16, 32, 4, 2048, 128},
{32, 32, 4, 1024, 128},
};
int n = sizeof(cfgs)/sizeof(cfgs[0]);
const int WARMUP = 10, ITERS = 100;
printf("\n===== DECODE BENCH (warmup=%d iters=%d) =====\n", WARMUP, ITERS);
printf("%-46s | %10s | %10s | %10s\n",
"config", "latency", "bandwidth", "throughput");
printf("---------------------------------------------------------------"
"----------------------------\n");
for (int ci = 0; ci < n; ci++) {
int B=cfgs[ci][0], Hq=cfgs[ci][1], Hk=cfgs[ci][2];
int sl=cfgs[ci][3], D=cfgs[ci][4];
size_t nQ=(size_t)B*Hq*D, nKV=(size_t)B*Hk*sl*D;
bf16 *dQ,*dK,*dV,*dO,*tmp;
cudaMalloc(&dQ,nQ*2); cudaMalloc(&dK,nKV*2);
cudaMalloc(&dV,nKV*2); cudaMalloc(&dO,nQ*2);
size_t big = nQ>nKV?nQ:nKV; tmp=new bf16[big];
for (size_t i=0;i<nQ;i++) tmp[i]=f2bf(randf());
cudaMemcpy(dQ,tmp,nQ*2,cudaMemcpyHostToDevice);
for (size_t i=0;i<nKV;i++) tmp[i]=f2bf(randf());
cudaMemcpy(dK,tmp,nKV*2,cudaMemcpyHostToDevice);
for (size_t i=0;i<nKV;i++) tmp[i]=f2bf(randf());
cudaMemcpy(dV,tmp,nKV*2,cudaMemcpyHostToDevice);
AttentionParams p;
p.batch=B; p.q_head=Hq; p.kv_head=Hk; p.q_len=1; p.kv_len=sl; p.head_dim=D;
p.use_mask=0; p.is_causal=0; p.causal_offset=0;
p.scale=1.0f/sqrtf((float)D);
p.q=dQ; p.k=dK; p.v=dV; p.mask=nullptr; p.o=dO;
DecodeScratch sc;
cudaMalloc(&sc.o_part, (size_t)B*Hq*32*D*sizeof(float));
cudaMalloc(&sc.ml_part, (size_t)B*Hq*32*2*sizeof(float));
for (int i=0;i<WARMUP;i++) dispatch_decode(p, sc);
cudaDeviceSynchronize();
cudaError_t err=cudaGetLastError();
if (err!=cudaSuccess){printf("CUDA err: %s\n",cudaGetErrorString(err));return;}
cudaEvent_t s,e; cudaEventCreate(&s); cudaEventCreate(&e);
cudaEventRecord(s);
for (int i=0;i<ITERS;i++) dispatch_decode(p, sc);
cudaEventRecord(e); cudaEventSynchronize(e);
float ms=0; cudaEventElapsedTime(&ms,s,e); ms/=ITERS;
double flops = 4.0*B*Hq*(double)sl*D;
double tflops = flops/(ms*1e-3)/1e12;
// HBM traffic: K + V read (B*Hk*sl*D each), bf16; Q/O negligible.
double bytes = 2.0 * (2.0*nKV);
double gbps = bytes/(ms*1e-3)/1e9;
char cfg[64];
snprintf(cfg, sizeof(cfg),
"B=%2d Hq=%2d Hk=%d q=%4d kv=%4d D=%3d causal=%d",
B,Hq,Hk,1,sl,D,0);
printf("%-46s | %7.4f ms | %7.1f GB/s | %6.2f TFLOP/s\n",
cfg, ms, gbps, tflops);
cudaFree(dQ);cudaFree(dK);cudaFree(dV);cudaFree(dO);
cudaFree(sc.o_part);cudaFree(sc.ml_part);
delete[]tmp; cudaEventDestroy(s); cudaEventDestroy(e);
}
}
int main() {
const int configs[][5] = {
{1, 2, 1, 64, 32}, // B,Hq,Hk,seq_len,D
{1, 32, 4, 512, 128},
{1, 32, 4, 1024, 128},
};
int n_cfgs = sizeof(configs) / sizeof(configs[0]);
for (int ci = 0; ci < n_cfgs; ci++) {
int B = configs[ci][0], Hq = configs[ci][1], Hk = configs[ci][2];
int sl = configs[ci][3], D = configs[ci][4], gs = Hq / Hk;
printf("=== B=%d Hq=%d Hk=%d seq=%d D=%d gs=%d ===\n", B,Hq,Hk,sl,D,gs);
size_t nQ = B*Hq*1*D, nKV = B*Hk*sl*D;
float *hQ=new float[nQ], *hK=new float[nKV], *hV=new float[nKV];
for (size_t i=0;i<nQ;i++) hQ[i]=randf();
for (size_t i=0;i<nKV;i++){hK[i]=randf();hV[i]=randf();}
bool* hMask=new bool[B*sl];
for (int i=0;i<B*sl;i++) hMask[i]=true;
bf16 *dQ,*dK,*dV,*dO,*tmp;
bool* dMask;
cudaMalloc(&dQ,nQ*2); cudaMalloc(&dK,nKV*2);
cudaMalloc(&dV,nKV*2); cudaMalloc(&dO,nQ*2);
cudaMalloc(&dMask,B*sl);
tmp=new bf16[max(nQ,nKV)];
for (size_t i=0;i<nQ;i++) tmp[i]=f2bf(hQ[i]);
cudaMemcpy(dQ,tmp,nQ*2,cudaMemcpyHostToDevice);
for (size_t i=0;i<nKV;i++) tmp[i]=f2bf(hK[i]);
cudaMemcpy(dK,tmp,nKV*2,cudaMemcpyHostToDevice);
for (size_t i=0;i<nKV;i++) tmp[i]=f2bf(hV[i]);
cudaMemcpy(dV,tmp,nKV*2,cudaMemcpyHostToDevice);
cudaMemcpy(dMask,hMask,B*sl,cudaMemcpyHostToDevice);
AttentionParams p;
p.batch=B; p.q_head=Hq; p.kv_head=Hk; p.q_len=1; p.kv_len=sl; p.head_dim=D;
p.use_mask=0; p.is_causal=0; p.causal_offset=0;
p.scale=1.0f/sqrtf((float)D);
p.q=dQ; p.k=dK; p.v=dV; p.mask=nullptr; p.o=dO;
// Split-K scratch (max 32 splits), sized for the production MMA path.
DecodeScratch sc;
cudaMalloc(&sc.o_part, (size_t)B*Hq*32*D*sizeof(float));
cudaMalloc(&sc.ml_part, (size_t)B*Hq*32*2*sizeof(float));
double t0=now_ms();
dispatch_decode(p, sc);
cudaDeviceSynchronize();
double kms=now_ms()-t0;
cudaError_t err=cudaGetLastError();
if (err!=cudaSuccess){printf("CUDA err: %s\n",cudaGetErrorString(err));return 1;}
bf16* hOut=new bf16[nQ];
cudaMemcpy(hOut,dO,nQ*2,cudaMemcpyDeviceToHost);
float* ref=new float[nQ];
cpu_decode(hQ,hK,hV,hMask,ref,B,Hq,Hk,sl,D);
float max_err=0;
for (size_t i=0;i<nQ;i++){
float d=fabsf(bf2f(hOut[i])-ref[i]);
if(d>max_err) max_err=d;
}
printf("kernel: %.3f ms max_err: %.6e\n\n",kms,max_err);
cudaFree(dQ);cudaFree(dK);cudaFree(dV);cudaFree(dO);cudaFree(dMask);
cudaFree(sc.o_part);cudaFree(sc.ml_part);
delete[]hQ;delete[]hK;delete[]hV;delete[]hMask;delete[]hOut;delete[]ref;delete[]tmp;
}
printf("All tests passed!\n");
bench();
return 0;
}
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