Update and rename test_simple_gla_for_mamba2.py to test_simple_gla.py

tests/ops/test_simple_gla.py

@@ -0,0 +1,71 @@
+# -*- coding: utf-8 -*-
+
+import pytest
+import torch
+
+from fla.ops.simple_gla import chunk_simple_gla
+
+
+@pytest.mark.parametrize("vary_A", [True, False])
+@pytest.mark.parametrize("dtype", [torch.float, torch.bfloat16])
+def test_simple_gla_to_mamba2(vary_A, dtype):
+    r"""
+    Map Mamba-2's `mamba_chunk_scan_combined` kernel to FLA's `simple_gla` kernel
+
+    Dependencies:
+    $ pip install mamba-ssm==2.2.2 triton==2.3.1
+
+    Reference: `ssd_minimal_discrete` and `test_correctness` in mamba repository:
+    https://github.com/state-spaces/mamba/blob/v2.2.2/mamba_ssm/modules/ssd_minimal.py#L82
+    """
+    from mamba_ssm.modules.ssd_minimal import ssd_minimal_discrete
+    from mamba_ssm.ops.triton.ssd_combined import mamba_chunk_scan_combined
+    torch.manual_seed(42)
+
+    # Dimensions, Denoted (B, T, Q, D, P) in Mamba2 paper
+    batch, seq_len, chunk_size, dim, headdim = 2, 512, 8, 64, 16
+    n_heads = dim // headdim  # (H) in the paper
+    ngroups = n_heads  # (G) in the paper; NOTE: do not use group-query here
+    dstate = 64  # (N) in the paper
+    device = "cuda"
+    atol = 5e-4 if dtype == torch.float else 1e-2
+
+    x = 0.1 * torch.randn(batch, seq_len, n_heads, headdim, dtype=dtype, device=device)
+    dt = torch.ones(batch, seq_len, n_heads, dtype=dtype, device=device)  # dt=1 can be ignored
+
+    if vary_A:
+        A = -0.1 * torch.rand(1, seq_len, n_heads, dtype=dtype, device=device)
+    else:  # constant A for all position
+        A = -0.1 * torch.rand(n_heads, dtype=dtype, device=device)
+
+    B = 0.1 * torch.randn(batch, seq_len, ngroups, dstate, dtype=dtype, device=device)
+    C = 0.1 * torch.randn(batch, seq_len, ngroups, dstate, dtype=dtype, device=device)
+
+    y_ssd, final_ssd = ssd_minimal_discrete(x * dt.unsqueeze(-1), A * dt, B, C, chunk_size)
+
+    if not vary_A:
+        # NOTE: fused kernel does not support varying A with time
+        y_fuse, final_fuse = mamba_chunk_scan_combined(x, dt, A, B, C, chunk_size, D=None, return_final_states=True)
+        assert y_ssd.allclose(y_fuse, 0, atol), f"y diff: {torch.abs(y_ssd - y_fuse).max()}"
+        # fused kernel upcasts state to float32
+        # https://github.com/state-spaces/mamba/blob/v2.2.2/mamba_ssm/ops/triton/ssd_combined.py#L650
+        final_fuse = final_fuse.to(dtype)
+        assert final_ssd.allclose(final_fuse, 0, atol), f"final diff: {torch.abs(final_ssd - final_fuse).max()}"
+
+    # mapping inputs Mamba2 -> FLA
+    # C, B, X: [batch, seq, head, hidden] -> [batch, head, seq, hidden]
+    # g: [batch, seq, head] -> [batch, head, seq]
+    q = C.transpose(1, 2)
+    k = B.transpose(1, 2)
+    v = x.transpose(1, 2)
+    g = (A * dt).transpose(1, 2)
+
+    # mapping outputs Mamba2 -> FLA
+    y_rearrange = y_ssd.transpose(1, 2)
+    final_rearrange = final_ssd.transpose(2, 3)
+
+    # comparing output results between FLA kernel and Mamba2 kernel
+    outputs_gla_fuse, final_gla_fuse = chunk_simple_gla(q, k, v, g, scale=1.0, output_final_state=True)
+    assert y_rearrange.allclose(outputs_gla_fuse, 0, atol), f"y diff: {torch.abs(y_rearrange - outputs_gla_fuse).max()}"
+    final_gla_fuse = final_gla_fuse.to(dtype)  # states hard-coded to float32 in FLA kernel
+    assert final_rearrange.allclose(final_gla_fuse, 0, atol), f"final diff: {torch.abs(final_ssd - final_gla_fuse).max()}"