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Debug: skip QK, write P directly to SMEM, 1 PV K-tile

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biondizzle
2026-05-28 14:26:36 +00:00
parent 11da4daa01
commit 9e13096bf8
1 changed files with 12 additions and 36 deletions
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48
tests/unit/test_fmha_smem_p.cu
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@@ -69,7 +69,8 @@ test_fmha_smem_p(const bf16_t* __restrict__ q, const bf16_t* __restrict__ k,
__syncthreads();
uint32_t tb = *sTmemBase;
// ===== STEP 1: QK GEMM =====
// ===== STEP 1: QK GEMM — SKIPPED =====
/*
{
uint64_t dq = make_umma_desc_kmajor_none(__cvta_generic_to_shared(sQ0), BLOCK_MN);
uint64_t dk = make_umma_desc_kmajor_none(__cvta_generic_to_shared(sK0), BLOCK_MN);
@@ -80,44 +81,19 @@ test_fmha_smem_p(const bf16_t* __restrict__ q, const bf16_t* __restrict__ k,
__syncthreads();
}
}
*/
// ===== STEP 2: Softmax — read S from TMEM, write P to SMEM =====
if (wid == 0) {
float s_vals[SK], row_max = -INFINITY;
for (int n = 0; n < SK / 8; n++) {
float tmp[8];
asm volatile("tcgen05.ld.sync.aligned.32x32b.x8.b32 {%0,%1,%2,%3,%4,%5,%6,%7},[%8];"
: "=f"(tmp[0]),"=f"(tmp[1]),"=f"(tmp[2]),"=f"(tmp[3]),
"=f"(tmp[4]),"=f"(tmp[5]),"=f"(tmp[6]),"=f"(tmp[7])
: "r"(tb + n*8));
asm volatile("tcgen05.wait::ld.sync.aligned;");
if (lane == 0) for (int c=0;c<8;c++) {
s_vals[n*8+c] = tmp[c] * scale;
row_max = fmaxf(row_max, tmp[c] * scale);
}
}
row_max = wmax(row_max);
float row_sum = 0.0f;
if (lane == 0) for (int j=0;j<SK;j++) {
s_vals[j] = expf(s_vals[j] - row_max);
row_sum += s_vals[j];
}
row_sum = wsum(row_sum);
if (lane == 0) for (int j=0;j<SK;j++) s_vals[j] /= row_sum;
// Write P to SMEM in canonical (128, 128) layout
// (128, 128): CORES_MN=16, CORES_K=16
// Only row 0 has data. Zero all, then write row 0.
for (int i = lane; i < 128 * SK; i += 32) sP[i] = 0;
if (lane == 0) {
for (int j = 0; j < SK; j++) {
int core_k = j / 8, lc = j % 8;
int dst_idx = core_k * 16 * 64 + 0 * 64 + 0 * 8 + lc;
sP[dst_idx] = f32_to_bf16(s_vals[j]);
}
// ===== STEP 2: Write P directly to SMEM (debug) =====
{
for (int i = tid; i < 128 * SK; i += 128) sP[i] = 0;
__syncthreads();
for (int j = tid; j < SK; j += 128) {
int core_k = j / 8, lc = j % 8;
int dst_idx = core_k * 16 * 64 + 0 * 64 + 0 * 8 + lc;
sP[dst_idx] = f32_to_bf16(0.1f);
}
__syncthreads();
}
__syncthreads();
// ===== STEP 3: PV GEMM (SS) =====
// P(128,128) × V(128,16) → O(128,16) via 8 SS MMA K-tiles