[Refactor][Example] Update linear attention examples and add tests (tile-ai#1010)

* [Refactor][Example] Update linear attention examples and add tests

- Refactored the backward and forward linear attention kernels to use shared memory and atomic additions for improved performance.
- Introduced L2 normalization in the main functions of both examples.
- Added a new test suite for the linear attention examples to ensure correctness and performance.
- Updated argument parsing in the main functions for better usability.

* upd docstring for tma atomic add

* lint

* Add flash-linear-attention dependency to requirements.txt

* Rename main function to chunk_linear_attn_bwd

* Rename main function to chunk_linear_attn_fwd

* chore

---------

Co-authored-by: LeiWang1999 <leiwang1999@outlook.com>
Co-authored-by: Lei Wang <34334180+LeiWang1999@users.noreply.github.com>

Author: Rachmanino

examples/linear_attention/example_linear_attn_bwd.py

@@ -1,19 +1,20 @@
 import torch
-import tilelang as tl
+import tilelang
 import tilelang.language as T
 from tilelang.profiler import do_bench
-
 import argparse
 from fla.ops.linear_attn import fused_chunk_linear_attn  # We compare with FLA
+from fla.modules.l2norm import l2norm_fwd
+from einops import rearrange
+from typing import Optional, Tuple
 
 
-@tl.jit(
-    out_idx=[4, 5, 6],
+@tilelang.jit(
     pass_configs={
-        "tl.disable_tma_lower": True,
-        "tl.disable_warp_specialized": True
+        tilelang.PassConfigKey.TL_DISABLE_TMA_LOWER: True,
+        tilelang.PassConfigKey.TL_DISABLE_WARP_SPECIALIZED: True,
     })
-def chunk_linear_attn_bwd_kernel(
+def tl_fused_chunk_bwd_kernel(
     B,
     S,
     H,
@@ -30,19 +31,19 @@ def chunk_linear_attn_bwd_kernel(
     chunk_size = 64
     BK = BV = 64  # Set to 128 can be faster, but has some numerical differences with FLA
     assert S % chunk_size == 0 and DK % BK == 0 and DV % BV == 0
-    NK = tl.cdiv(DK, BK)
-    NV = tl.cdiv(DV, BV)
-    NT = tl.cdiv(S, chunk_size)
+    NK = tilelang.cdiv(DK, BK)
+    NV = tilelang.cdiv(DV, BV)
+    NT = tilelang.cdiv(S, chunk_size)
 
     @T.prim_func
-    def chunk_linear_attn_bwd(
+    def fused_chunk_linear_attn_bwd(
             Q: T.Tensor([B, S, H, DK], dtype),  # type: ignore
             K: T.Tensor([B, S, H, DK], dtype),  # type: ignore
             V: T.Tensor([B, S, H, DV], dtype),  # type: ignore
             dO: T.Tensor([B, S, H, DV], dtype),  # type: ignore
-            dQ: T.Tensor([NV, B, S, H, DK], dtype),  # type: ignore
-            dK: T.Tensor([NV, B, S, H, DK], dtype),  # type: ignore
-            dV: T.Tensor([NK, B, S, H, DV], dtype),  # type: ignore
+            dQ: T.Tensor([B, S, H, DK], accum_dtype),  # type: ignore
+            dK: T.Tensor([B, S, H, DK], accum_dtype),  # type: ignore
+            dV: T.Tensor([B, S, H, DV], accum_dtype),  # type: ignore
     ):
         with T.Kernel(NV, NK, B * H) as (i_v, i_k, i_bh):
             i_b = i_bh // H
@@ -51,8 +52,11 @@ def chunk_linear_attn_bwd(
             ds = T.alloc_fragment([chunk_size, chunk_size], accum_dtype)
             ds_shared = T.alloc_shared([chunk_size, chunk_size], dtype)
             dq = T.alloc_fragment([chunk_size, BK], accum_dtype)
+            dq_shared = T.alloc_shared([chunk_size, BK], accum_dtype)
             dk = T.alloc_fragment([chunk_size, BK], accum_dtype)
+            dk_shared = T.alloc_shared([chunk_size, BK], accum_dtype)
             dv = T.alloc_fragment([chunk_size, BV], accum_dtype)
+            dv_shared = T.alloc_shared([chunk_size, BV], accum_dtype)
             q = T.alloc_shared([chunk_size, BK], dtype)
             k = T.alloc_shared([chunk_size, BK], dtype)
             v = T.alloc_shared([chunk_size, BV], dtype)
@@ -61,22 +65,19 @@ def chunk_linear_attn_bwd(
             h_shared = T.alloc_shared([BV, BK], dtype)
             dh = T.alloc_fragment([BK, BV], accum_dtype)
             dh_shared = T.alloc_shared([BK, BV], dtype)
-            T.clear(h)
-            T.clear(dh)
 
             T.annotate_layout({
-                ds_shared: tl.layout.make_swizzled_layout(ds_shared),
-                q: tl.layout.make_swizzled_layout(q),
-                k: tl.layout.make_swizzled_layout(k),
-                v: tl.layout.make_swizzled_layout(v),
-                do: tl.layout.make_swizzled_layout(do),
-                h_shared: tl.layout.make_swizzled_layout(h_shared),
-                dh_shared: tl.layout.make_swizzled_layout(dh_shared)
+                dq_shared: tilelang.layout.make_swizzled_layout(dq_shared),
+                dk_shared: tilelang.layout.make_swizzled_layout(dk_shared),
+                dv_shared: tilelang.layout.make_swizzled_layout(dv_shared)
             })
             T.use_swizzle(10)
 
+            T.clear(h)
+            T.clear(dh)
+
             # Calculate dQ
-            for i in T.Pipelined(0, NT, num_stages=1):
+            for i in T.Pipelined(0, NT):
                 T.copy(K[i_b, i * chunk_size:(i + 1) * chunk_size, i_h, i_k * BK:(i_k + 1) * BK], k)
                 T.copy(V[i_b, i * chunk_size:(i + 1) * chunk_size, i_h, i_v * BV:(i_v + 1) * BV], v)
                 T.copy(dO[i_b, i * chunk_size:(i + 1) * chunk_size, i_h, i_v * BV:(i_v + 1) * BV],
@@ -92,12 +93,13 @@ def chunk_linear_attn_bwd(
                 T.gemm(v, k, h, transpose_A=True)
                 for row, col in T.Parallel(chunk_size, BK):
                     dq[row, col] *= scale
-                T.copy(
-                    dq, dQ[i_v, i_b, i * chunk_size:(i + 1) * chunk_size, i_h,
-                           i_k * BK:(i_k + 1) * BK])
+                T.copy(dq, dq_shared)
+                T.atomic_add(
+                    dQ[i_b, i * chunk_size:(i + 1) * chunk_size, i_h, i_k * BK:(i_k + 1) * BK],
+                    dq_shared)
 
             # Calculate dK, dV (reversely)
-            for i in T.Pipelined(1, NT + 1, num_stages=1):
+            for i in T.Pipelined(1, NT + 1):
                 start = NT - i
                 for row, col in T.Parallel(chunk_size, BK):
                     q[row, col] = Q[i_b, start * chunk_size + row, i_h, i_k * BK + col] * scale
@@ -131,53 +133,90 @@ def chunk_linear_attn_bwd(
                 # Update dh
                 T.gemm(q, do, dh, transpose_A=True)
 
-                T.copy(
-                    dk, dK[i_v, i_b, start * chunk_size:(start + 1) * chunk_size, i_h,
-                           i_k * BK:(i_k + 1) * BK])
-                T.copy(
-                    dv, dV[i_k, i_b, start * chunk_size:(start + 1) * chunk_size, i_h,
-                           i_v * BV:(i_v + 1) * BV])
-
-    return chunk_linear_attn_bwd
-
-
-def postprocess(dQ, dK, dV):
-    dQ = dQ[0] if dQ.size(0) == 1 else dQ.sum(0)
-    dK = dK[0] if dK.size(0) == 1 else dK.sum(0)
-    dV = dV[0] if dV.size(0) == 1 else dV.sum(0)
-    return dQ, dK, dV
-
-
-def main():
-    parser = argparse.ArgumentParser()
-    parser.add_argument('--B', type=int, default=8, help='Batch size')
-    parser.add_argument('--S', type=int, default=4096, help='Seq len')
-    parser.add_argument('--H', type=int, default=32, help='Num heads')
-    parser.add_argument('--D', type=int, default=256, help='Head dim')
-    args = parser.parse_args()
-    B, S, H, D = args.B, args.S, args.H, args.D
-
+                T.copy(dk, dk_shared)
+                T.atomic_add(
+                    dK[i_b, start * chunk_size:(start + 1) * chunk_size, i_h,
+                       i_k * BK:(i_k + 1) * BK], dk_shared)
+                T.copy(dv, dv_shared)
+                T.atomic_add(
+                    dV[i_b, start * chunk_size:(start + 1) * chunk_size, i_h,
+                       i_v * BV:(i_v + 1) * BV], dv_shared)
+
+    return fused_chunk_linear_attn_bwd
+
+
+def tl_fused_chunk_bwd(Q, K, V, dO):
+    B, S, H, D = Q.shape
+    kernel = tl_fused_chunk_bwd_kernel(B, S, H, D, D)
+    dQ = torch.zeros_like(Q, dtype=torch.float32)
+    dK = torch.zeros_like(K, dtype=torch.float32)
+    dV = torch.zeros_like(V, dtype=torch.float32)
+    kernel(Q, K, V, dO, dQ, dK, dV)
+    return dQ.to(torch.float16), dK.to(torch.float16), dV.to(torch.float16)
+
+
+def ref_program(q: torch.Tensor,
+                k: torch.Tensor,
+                v: torch.Tensor,
+                scale: Optional[float] = None) -> Tuple[torch.Tensor, torch.Tensor]:
+    q, k, v = q.float(), k.float(), v.float()
+    if scale is None:
+        scale = q.shape[-1]**-0.5
+    chunk_size = 64
+    q = rearrange(q, 'b (n c) h d -> b h n c d', c=chunk_size) * scale
+    k = rearrange(k, 'b (n c) h d -> b h n c d', c=chunk_size)
+    v = rearrange(v, 'b (n c) h d -> b h n c d', c=chunk_size)
+    kv = k.transpose(-1, -2) @ v
+    kv = kv.cumsum(2)
+    h = kv[:, :, -1, :, :]
+    kv = torch.cat([torch.zeros_like(kv[:, :, :1]), kv[:, :, :-1]], dim=2)
+    inter = q @ kv
+    intra = ((q @ k.transpose(-1, -2)).masked_fill_(
+        torch.triu(torch.ones(chunk_size, chunk_size, dtype=bool, device=q.device), diagonal=1),
+        0)) @ v
+    o = inter + intra
+    return rearrange(o, 'b h n c d -> b (n c) h d'), h
+
+
+def main(B=1, S=1024, H=16, D=128):
     q = torch.randn((B, S, H, D), device='cuda', dtype=torch.float16, requires_grad=True)
     k = torch.randn((B, S, H, D), device='cuda', dtype=torch.float16, requires_grad=True)
     v = torch.randn((B, S, H, D), device='cuda', dtype=torch.float16, requires_grad=True)
     do = torch.randn((B, S, H, D), device='cuda', dtype=torch.float16)
 
-    kernel = chunk_linear_attn_bwd_kernel(B, S, H, D, D)
-    dq, dk, dv = postprocess(*kernel(q, k, v, do))
-    o_ref, _ = fused_chunk_linear_attn(q, k, v, output_final_state=True, normalize=False)
+    # qk norm is necessary for linear attn
+    q = l2norm_fwd(q)[0].requires_grad_(True)
+    k = l2norm_fwd(k)[0].requires_grad_(True)
+
+    dq, dk, dv = tl_fused_chunk_bwd(q, k, v, do)
+    q.grad = k.grad = v.grad = None
+    o_ref, _ = ref_program(q, k, v)
     o_ref.backward(do, retain_graph=True)
-    if torch.allclose(dq, q.grad) and torch.allclose(dk, k.grad) and torch.allclose(dv, v.grad):
-        print('Passed all tests!✅')
-    else:
-        print('Failed some tests!❌')
-    t1 = do_bench(lambda: o_ref.backward(do, retain_graph=True), warmup=25, rep=100)
+
+    assert torch.allclose(
+        dq, q.grad, atol=1e-2, rtol=1e-2), f'dq max err: {(dq - q.grad).abs().max()}'
+    assert torch.allclose(
+        dk, k.grad, atol=1e-2, rtol=1e-2), f'dk max err: {(dk - k.grad).abs().max()}'
+    assert torch.allclose(
+        dv, v.grad, atol=1e-2, rtol=1e-2), f'dv max err: {(dv - v.grad).abs().max()}'
+    print('Passed all tests!✅')
+
+    # Benchmark
     q.grad = k.grad = v.grad = None
     o_ref, _ = fused_chunk_linear_attn(q, k, v, output_final_state=True, normalize=False)
-    t2 = do_bench(lambda: postprocess(*kernel(q, k, v, do)), warmup=25, rep=100)
+    t1 = do_bench(lambda: o_ref.backward(do, retain_graph=True), backend='cupti')
+    t2 = do_bench(lambda: tl_fused_chunk_bwd(q, k, v, do), backend='cupti')
     print(f'Triton latency: {t1:.3f} ms')
     print(f'TileLang latency: {t2:.3f} ms')
     print(f'Speedup: {t1/t2:.3f}x')
 
 
 if __name__ == '__main__':
-    main()
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--B', type=int, default=8, help='Batch size')
+    parser.add_argument('--S', type=int, default=1024, help='Seq len')
+    parser.add_argument('--H', type=int, default=32, help='Num heads')
+    parser.add_argument('--D', type=int, default=128, help='Head dim')
+    args = parser.parse_args()
+
+    main(args.B, args.S, args.H, args.D)