D2: add initial multi-head test file

tests/unit/test_d2_multihead.py

@@ -0,0 +1,118 @@
+"""
+FMHA D2: Multi-Query Grid with Head Packing.
+
+Start with n_h=1 (regression), then n_h=2, n_h=8, etc.
+Uses s_k=128 (1 KV tile, no O rescale needed).
+
+Strategy B: Head as grid dimension.
+Grid: (ceil_div(T, 128), num_query_heads, batch)
+Each CTA handles one query head.
+"""
+import torch, math
+import cutlass.cute as cute
+import cutlass.torch as ct
+import cuda.bindings.driver as cuda
+from dsv4.kernels.attention.fmha import FmhaKernel
+
+
+def test_multihead(hd=64, n_h=1, batch=1, T=128, s_k=128):
+    torch.manual_seed(42)
+
+    # Q: (batch, n_h, T, hd)
+    q = torch.randn(batch, n_h, T, hd, dtype=torch.bfloat16, device='cuda')
+    # K/V: (batch, 1, s_k, hd) — MQA: shared KV
+    k = torch.randn(batch, 1, s_k, hd, dtype=torch.bfloat16, device='cuda')
+    v = torch.randn(batch, 1, s_k, hd, dtype=torch.bfloat16, device='cuda')
+    # O: (batch, n_h, T, hd)
+    o = torch.zeros(batch, n_h, T, hd, dtype=torch.bfloat16, device='cuda')
+    # LSE: (batch, n_h, T)
+    lse = torch.zeros(batch, n_h, T, dtype=torch.float32, device='cuda')
+
+    # FP32 reference
+    qf = q.float()  # (batch, n_h, T, hd)
+    kf = k[:, 0].float()  # (batch, s_k, hd) — shared KV
+    vf = v[:, 0].float()  # (batch, s_k, hd)
+    scale = 1.0 / math.sqrt(hd)
+
+    ref_o = torch.zeros(batch, n_h, T, hd, dtype=torch.float32, device='cuda')
+    for b in range(batch):
+        for h in range(n_h):
+            attn = qf[b, h] @ kf[b].T * scale  # (T, s_k)
+            attn_max = attn.max(dim=-1, keepdim=True)[0]
+            attn_exp = torch.exp(attn - attn_max)
+            attn_sum = attn_exp.sum(dim=-1, keepdim=True)
+            ref_o[b, h] = (attn_exp / attn_sum) @ vf[b]
+
+    # For now, test with n_h=1 to verify the kernel works.
+    # D2 multi-head requires kernel changes (grid, TMA, etc.)
+    # This test will FAIL until D2 is implemented in the kernel.
+    
+    # Current kernel expects Q: (T, hd, 1), K: (s_k, hd, 1), V: (s_k, hd)
+    # For n_h=1, this is just a reshape.
+    if n_h == 1 and batch == 1:
+        q_kernel = q[0, 0].unsqueeze(-1)  # (T, hd, 1)
+        k_kernel = k[0, 0].unsqueeze(-1)  # (s_k, hd, 1)
+        v_kernel = v[0, 0]  # (s_k, hd)
+
+        kernel = FmhaKernel(head_dim=hd, s_k=s_k, use_smem_p=False, normalize=False)
+        pv_n_tile = kernel.pv_n_tile
+        stream = cuda.CUstream(torch.cuda.current_stream().cuda_stream)
+
+        # For hd=64, n_pv_tiles=1, but we handle general case
+        n_pv_tiles = hd // pv_n_tile
+        o_kernel = torch.zeros(T, hd, dtype=torch.float32, device='cuda')
+
+        # Compile
+        v_tile = v_kernel[:, 0:pv_n_tile].contiguous()
+        v_k = v_tile.unsqueeze(-1)
+        c_tile = torch.zeros(T, pv_n_tile, 1, dtype=torch.bfloat16, device='cuda')
+        lse_t = torch.zeros(T, dtype=torch.float32, device='cuda')
+
+        mQ = ct.from_dlpack(q_kernel).mark_layout_dynamic(leading_dim=ct.get_leading_dim(q_kernel))
+        mK = ct.from_dlpack(k_kernel).mark_layout_dynamic(leading_dim=ct.get_leading_dim(k_kernel))
+        mV = ct.from_dlpack(v_k).mark_layout_dynamic(leading_dim=ct.get_leading_dim(v_k))
+        mC = ct.from_dlpack(c_tile).mark_layout_dynamic(leading_dim=ct.get_leading_dim(c_tile))
+        mLSE = ct.from_dlpack(lse_t).mark_layout_dynamic(leading_dim=ct.get_leading_dim(lse_t))
+
+        print(f'  Compiling (hd={hd}, n_h={n_h}, T={T}, s_k={s_k})...', flush=True)
+        compiled = cute.compile(kernel, mQ, mK, mV, mC, stream, mLSE)
+
+        for nt in range(n_pv_tiles):
+            v_start = nt * pv_n_tile
+            v_end = v_start + pv_n_tile
+            v_tile = v_kernel[:, v_start:v_end].contiguous()
+            v_k = v_tile.unsqueeze(-1)
+            c_tile = torch.zeros(T, pv_n_tile, 1, dtype=torch.bfloat16, device='cuda')
+            lse_t.zero_()
+
+            mQ = ct.from_dlpack(q_kernel).mark_layout_dynamic(leading_dim=ct.get_leading_dim(q_kernel))
+            mK = ct.from_dlpack(k_kernel).mark_layout_dynamic(leading_dim=ct.get_leading_dim(k_kernel))
+            mV = ct.from_dlpack(v_k).mark_layout_dynamic(leading_dim=ct.get_leading_dim(v_k))
+            mC = ct.from_dlpack(c_tile).mark_layout_dynamic(leading_dim=ct.get_leading_dim(c_tile))
+            mLSE = ct.from_dlpack(lse_t).mark_layout_dynamic(leading_dim=ct.get_leading_dim(lse_t))
+
+            compiled(mQ, mK, mV, mC, stream, mLSE)
+            torch.cuda.synchronize()
+
+            o_kernel[:, v_start:v_end] = c_tile[:, :, 0].float()
+
+        cos = torch.nn.functional.cosine_similarity(
+            o_kernel.flatten().unsqueeze(0), ref_o[0, 0].flatten().unsqueeze(0)
+        ).item()
+        print(f'  hd={hd}, n_h={n_h}, T={T}, s_k={s_k}: cos {cos:.6f}  {"PASS" if cos >= 0.99 else "FAIL"}')
+    else:
+        print(f'  n_h={n_h}, batch={batch}: SKIPPED (D2 multi-head not yet implemented)')
+
+
+def test():
+    print("=== D2: Multi-Query Grid ===\n")
+
+    # Regression: n_h=1 (same as existing tests)
+    test_multihead(64, 1, 1, 128, 128)
+
+    # n_h=2 (first multi-head test, will need kernel changes)
+    test_multihead(64, 2, 1, 128, 128)
+
+
+if __name__ == '__main__':
+    test()