[torch.compile] rework compile control with piecewise cudagraph (#9715)

Signed-off-by: youkaichao <youkaichao@gmail.com>

tests/compile/piecewise/test_simple.py

@@ -0,0 +1,96 @@
+"""
+Test the piecewise compilation with a simple model so that we
+can exactly calculate the expected output and side effects.
+"""
+import os
+
+import torch
+from torch import nn
+
+from vllm.compilation.compile_context import set_compile_context
+from vllm.compilation.counter import compilation_counter
+from vllm.compilation.decorators import support_torch_compile
+from vllm.compilation.levels import CompilationLevel
+
+os.environ["VLLM_TORCH_COMPILE_LEVEL"] = str(CompilationLevel.PIECEWISE)
+
+global_counter = 0
+
+
+@torch.library.custom_op("silly::attention", mutates_args=["out"])
+def silly_attention(q: torch.Tensor, k: torch.Tensor, v: torch.Tensor,
+                    out: torch.Tensor) -> None:
+    global global_counter
+    global_counter += 1
+    print(f"{global_counter=}")
+    out.copy_(q)
+    out[0] += 1
+
+
+@silly_attention.register_fake
+def _(q: torch.Tensor, k: torch.Tensor, v: torch.Tensor,
+      out: torch.Tensor) -> None:
+    return
+
+
+@support_torch_compile
+class SillyModel(nn.Module):
+
+    def __init__(self) -> None:
+        super().__init__()
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        """
+        Overall effect:
+        x += 1
+        x[0] += 2
+        global_counter += 2
+        """
+        x = x + 1
+        x = x + 2
+        out = torch.empty_like(x)
+        torch.ops.silly.attention(x, x, x, out)
+        x = out
+        x = x - 2
+        x = x - 1
+        out = torch.empty_like(x)
+        torch.ops.silly.attention(x, x, x, out)
+        x = out
+        x = x + 1
+        return x
+
+
+def test_simple_piecewise_compile():
+
+    model = SillyModel()
+
+    directory = os.path.dirname(__file__)
+    config = os.path.join(directory, "piecewise_compilation_config.json")
+    os.environ["VLLM_TORCH_COMPILE_CONFIG"] = config
+
+    input_buffer = torch.randn(100).cuda()
+
+    with compilation_counter.expect(
+            num_graphs_seen=1,  # one graph for the model
+            num_piecewise_graphs_seen=5,  # 2 * num_layers + 1
+            num_piecewise_capturable_graphs_seen=3,  # 1 + num_layers
+            num_inductor_compilations=3,  # num_piecewise_capturable_graphs_seen
+            num_cudagraph_caputured=
+            6,  # num_cudagraph_sizes * num_piecewise_capturable_graphs_seen
+    ):
+
+        with set_compile_context([1, 2]):
+            model(input_buffer)
+
+            model(input_buffer[:2])
+            model(input_buffer[:1])
+
+        input_buffer[:2].zero_()
+        global global_counter
+        global_counter = 0
+        output = model(input_buffer[:2])
+        assert global_counter == 2
+        assert torch.allclose(output.cpu(), torch.tensor([3., 1.]))
+
+    # clean up to avoid side effects for other tests
+    del os.environ["VLLM_TORCH_COMPILE_CONFIG"]