[RFC] Implement caching for user defined triton kernels (pytorch#140326)

This PR adds caching for user defined triton kernels by putting the transitive closure of source code in node.meta along with constant arguments.

One HUGE hack we do here is a node looks like
```
triton_kernel_wrapper_functional_proxy = torch.ops.higher_order.triton_kernel_wrapper_functional(kernel_idx = 0, constant_args_idx = 1, grid = [(1, 1, 1)], tma_descriptor_
metadata = {}, kwargs = {'in_ptr0': arg0_1, 'in_ptr1': arg1_1, 'out_ptr': arg0_1}, tensors_to_clone = ['out_ptr']);
```
so we use regex to remove `kernel_idx = 0, constant_args_idx = 1` parts as they are not relevant to cache hash. This is horrible and I'd like to eventually not use pickle as a hashing alternative but this is a longer project.

Differential Revision: [D65895744](https://our.internmc.facebook.com/intern/diff/D65895744)
Pull Request resolved: pytorch#140326
Approved by: https://github.com/zou3519

Author: oulgen

test/inductor/test_codecache.py

@@ -49,7 +49,7 @@
 if HAS_TRITON:
     import triton  # @manual
 
-    from torch.testing._internal.triton_utils import add_kernel
+    from torch.testing._internal.triton_utils import add_kernel, sub_kernel
 
 torch._dynamo.config.fake_tensor_cache_enabled = True
 torch._dynamo.config.fake_tensor_cache_crosscheck_enabled = True
@@ -494,13 +494,41 @@ def fn2(q, k, v):
     @config.patch({"fx_graph_cache": True})
     @config.patch({"fx_graph_remote_cache": False})
     @parametrize("bundle_triton", (False, True))
-    @parametrize("grad", (False, True))
-    def test_triton_higher_order_op_bypass(self, bundle_triton, grad):
+    def test_higher_order_op_bypass(self, bundle_triton):
         """
-        Verify that we bypass the cache when we have a triton higher order ops
+        Verify that we bypass the cache when we have a higher order ops
         and that bundler start/end works with a cache bypass.
         """
 
+        def fn(x):
+            def true_fn(x: torch.Tensor):
+                return x.cos()
+
+            def false_fn(x: torch.Tensor):
+                return x.sin()
+
+            return torch.cond(x.shape[0], true_fn, false_fn, (x,))
+
+        with config.patch(bundle_triton_into_fx_graph_cache=bundle_triton):
+            compiled_fn = torch.compile(fn, dynamic=True, fullgraph=True)
+
+            x = torch.randn(4, 4, device=GPU_TYPE)
+            result = compiled_fn(x)
+
+            self.assertEqual(counters["inductor"]["fxgraph_cache_miss"], 0)
+            self.assertEqual(counters["inductor"]["fxgraph_cache_hit"], 0)
+            self.assertGreater(counters["inductor"]["fxgraph_cache_bypass"], 0)
+
+    @requires_gpu()
+    @requires_triton()
+    @config.patch({"fx_graph_cache": True})
+    @config.patch({"fx_graph_remote_cache": False})
+    @parametrize("bundle_triton", (False, True))
+    def test_triton_higher_order_op(self, bundle_triton):
+        """
+        Verify that we can cache user defined triton kernel higher order op
+        """
+
         def fn(x, y):
             n_elements = x.numel()
             grid = lambda meta: (  # noqa: E731
@@ -509,18 +537,54 @@ def fn(x, y):
             add_kernel[grid](x, y, x, n_elements, BLOCK_SIZE=4)
             return x
 
+        def fn2(x, y):
+            n_elements = x.numel()
+            grid = lambda meta: (  # noqa: E731
+                triton.cdiv(n_elements, meta["BLOCK_SIZE"]),
+            )
+            sub_kernel[grid](x, y, x, n_elements, BLOCK_SIZE=4)
+            return x
+
         with config.patch(bundle_triton_into_fx_graph_cache=bundle_triton):
             compiled_fn = torch.compile(fn, fullgraph=True)
+            compiled_fn2 = torch.compile(fn2, fullgraph=True)
+
+            x = torch.randn(4, device=GPU_TYPE)
+            y = torch.randn(4, device=GPU_TYPE)
 
-            x = torch.randn(4, device=GPU_TYPE, requires_grad=grad)
-            y = torch.randn(4, device=GPU_TYPE, requires_grad=grad)
             result = compiled_fn(x, y)
-            if grad:
-                result.sum().backward()
 
-            self.assertEqual(counters["inductor"]["fxgraph_cache_miss"], 0)
+            self.assertEqual(counters["inductor"]["fxgraph_cache_miss"], 1)
             self.assertEqual(counters["inductor"]["fxgraph_cache_hit"], 0)
-            self.assertGreater(counters["inductor"]["fxgraph_cache_bypass"], 0)
+            self.assertEqual(counters["inductor"]["fxgraph_cache_bypass"], 0)
+
+            # A second call should hit. (First reset so in-memory guards
+            # don't prevent compilation).
+            self.reset()
+
+            # Clean PyCodeCache and triton kernels
+            PyCodeCache.cache_clear()
+            shutil.rmtree(os.path.join(cache_dir(), "triton"), ignore_errors=True)
+
+            result = compiled_fn(x, y)
+
+            self.assertEqual(counters["inductor"]["fxgraph_cache_miss"], 1)
+            self.assertEqual(counters["inductor"]["fxgraph_cache_hit"], 1)
+            self.assertEqual(counters["inductor"]["fxgraph_cache_bypass"], 0)
+
+            # A second call should hit. (First reset so in-memory guards
+            # don't prevent compilation).
+            self.reset()
+
+            # Clean PyCodeCache and triton kernels
+            PyCodeCache.cache_clear()
+            shutil.rmtree(os.path.join(cache_dir(), "triton"), ignore_errors=True)
+
+            result = compiled_fn2(x, y)
+
+            self.assertEqual(counters["inductor"]["fxgraph_cache_miss"], 2)
+            self.assertEqual(counters["inductor"]["fxgraph_cache_hit"], 1)
+            self.assertEqual(counters["inductor"]["fxgraph_cache_bypass"], 0)
 
     @config.patch({"fx_graph_cache": True})
     @config.patch({"fx_graph_remote_cache": False})
@@ -808,15 +872,16 @@ def test_tensor_constants(self):
         self.assertFalse(GraphLowering.can_inline_constant(large))
 
         # By default, we hash the metadata and values independent of the size.
-        pickler = FxGraphCachePickler()
+        gm = torch.fx.GraphModule({}, torch.fx.Graph())
+        pickler = FxGraphCachePickler(gm)
 
         data = pickler.dumps(small)
         self.assertIsInstance(pickle.loads(data), TensorMetadataAndValues)
         data = pickler.dumps(large)
         self.assertIsInstance(pickle.loads(data), TensorMetadataAndValues)
 
         # If include_non_inlined=False, we only hash the values of small tensors.
-        pickler = FxGraphCachePickler(False)
+        pickler = FxGraphCachePickler(gm, False)
 
         data = pickler.dumps(small)
         self.assertIsInstance(pickle.loads(data), TensorMetadataAndValues)
@@ -827,7 +892,8 @@ def test_hash_fake_tensors(self):
         """
         Test hashing (pickling) FakeTensors with various characteristics.
         """
-        pickler = FxGraphCachePickler()
+        gm = torch.fx.GraphModule({}, torch.fx.Graph())
+        pickler = FxGraphCachePickler(gm)
         with torch._subclasses.FakeTensorMode():
             # Verify that FakeTensors get pickled into a TensorMetadata:
             data = pickler.dumps(torch.randn(1))
@@ -933,7 +999,8 @@ def test_hash_kwargs(self):
         Test the special handling of the kwargs when hashing, i.e.,
         ordering of the kwargs dict and any set arguments.
         """
-        pickler = FxGraphCachePickler()
+        gm = torch.fx.GraphModule({}, torch.fx.Graph())
+        pickler = FxGraphCachePickler(gm)
 
         # Dict order of the kwargs should not affect hashes.
         details1 = FxGraphHashDetails(None, [], {"a": 0, "z": 1}, [])
@@ -981,7 +1048,8 @@ def test_hash_config_changes(self):
         with config.patch({"max_autotune": True}):
             details3 = FxGraphHashDetails(None, [], {}, [])
 
-        pickler = FxGraphCachePickler()
+        gm = torch.fx.GraphModule({}, torch.fx.Graph())
+        pickler = FxGraphCachePickler(gm)
 
         self.assertEqual(
             pickler.dumps(details1),
@@ -1016,7 +1084,8 @@ def uuid(self) -> Optional[Union[bytes, str]]:
             custom_pass._uuid = "2"
             details3 = FxGraphHashDetails(None, [], {}, [])
 
-            pickler = FxGraphCachePickler()
+            gm = torch.fx.GraphModule({}, torch.fx.Graph())
+            pickler = FxGraphCachePickler(gm)
 
             self.assertEqual(
                 pickler.dumps(details1),
@@ -1031,8 +1100,9 @@ def test_bypass_unsupported(self):
         """
         Test _reduce_unsupported
         """
+        gm = torch.fx.GraphModule({}, torch.fx.Graph())
         with self.assertRaises(BypassFxGraphCache):
-            FxGraphCachePickler().dumps(
+            FxGraphCachePickler(gm).dumps(
                 torch.fx.experimental._backward_state.BackwardState()
             )
 
@@ -1047,7 +1117,8 @@ def test_stable_strings(self):
 
         self.assertNotEqual(id(s1), id(s2))
 
-        pickler = FxGraphCachePickler()
+        gm = torch.fx.GraphModule({}, torch.fx.Graph())
+        pickler = FxGraphCachePickler(gm)
         self.assertEqual(
             pickler.dumps([s1, s1]),
             pickler.dumps([s1, s2]),

torch/_functorch/_aot_autograd/autograd_cache.py

@@ -227,8 +227,8 @@ def __init__(
 
 
 class AOTAutogradCachePickler(FxGraphCachePickler):
-    def __init__(self):
-        super().__init__()
+    def __init__(self, gm: torch.fx.GraphModule):
+        super().__init__(gm)
         self.dispatch_table: Dict
         self.dispatch_table.update(
             {
@@ -275,7 +275,7 @@ def autograd_cache_key(
     """
     check_cacheable(gm)
     details = AOTAutogradCacheDetails(gm, example_inputs, config, fx_config)
-    pickler = AOTAutogradCachePickler()
+    pickler = AOTAutogradCachePickler(gm)
     # The prefix distinguishes among the other kinds of objects we cache
     key = "a" + pickler.get_hash(details)
     debug_lines = pickler.debug_lines(details)

torch/_higher_order_ops/triton_kernel_wrap.py

@@ -613,7 +613,7 @@ def identify_mutated_tensors(
 # Used for wrapping a Triton Kernel
 class TritonKernelWrapperMutation(HigherOrderOperator):
     def __init__(self) -> None:
-        super().__init__("triton_kernel_wrapper_mutation", cacheable=False)
+        super().__init__("triton_kernel_wrapper_mutation", cacheable=True)
 
     def __call__(
         self,
@@ -638,7 +638,7 @@ def __call__(
 # Used for wrapping a Triton Kernel in a functional manner
 class TritonKernelWrapperFunctional(HigherOrderOperator):
     def __init__(self) -> None:
-        super().__init__("triton_kernel_wrapper_functional", cacheable=False)
+        super().__init__("triton_kernel_wrapper_functional", cacheable=True)
 
     def __call__(
         self,
@@ -774,6 +774,26 @@ def trace_triton_kernel_wrapper(
         proxy_args,
         name=func_overload.__name__ + "_proxy",
     )
+
+    from triton.runtime.autotuner import Autotuner
+
+    from torch._inductor.codegen.wrapper import (
+        user_defined_triton_kernel_transitive_closure_source_code,
+    )
+
+    kernel = kernel_side_table.get_kernel(proxy_args["kernel_idx"])
+    if isinstance(kernel, Autotuner):
+        kernel = kernel.fn
+
+    kernel_source = user_defined_triton_kernel_transitive_closure_source_code(kernel)
+    constant_args = kernel_side_table.get_constant_args(proxy_args["constant_args_idx"])
+    # we add to node here so that it gets included in the inductor cache key
+    # when the graph is pickled
+    out_proxy.node.meta["user_defined_triton_kernel_source_and_constant_args"] = (
+        kernel_source,
+        constant_args,
+    )
+
     ret = track_tensor_tree(out, out_proxy, constant=None, tracer=proxy_mode.tracer)
     return ret
 

torch/_inductor/codecache.py

@@ -7,6 +7,7 @@
 import hashlib
 import importlib
 import io
+import itertools
 import json
 import logging
 import os
@@ -525,7 +526,12 @@ class FxGraphCachePickler(pickle.Pickler):
     data that allow us to compute a stable, but safe hash.
     """
 
-    def __init__(self, include_non_inlined: bool = True) -> None:
+    def __init__(
+        self,
+        gm: torch.fx.GraphModule,
+        include_non_inlined: bool = True,
+        has_user_defined_triton_kernels: bool = False,
+    ) -> None:
         """
         Create an FX graph pickler. If include_non_inlined=True, then pickling will
         include the _values_ for all Tensors. (Note that any tensors are constants
@@ -548,6 +554,11 @@ def __init__(self, include_non_inlined: bool = True) -> None:
                 ),
             }
         )
+        if has_user_defined_triton_kernels:
+            # Need to use runtime type as GraphModule generates a singleton in __new__ function
+            self.dispatch_table[gm.__class__] = functools.partial(
+                self._reduce_graph_module
+            )
 
         # Run with pickler.fast so it doesn't intern strings, making the hash result more predictable
         # TODO: pickler.fast is technically deprecated. Will this work on new python versions?
@@ -614,6 +625,25 @@ def _reduce_unsupported(self, s: Any) -> NoReturn:
         """
         raise BypassFxGraphCache("Reduce unsupported")
 
+    def _reduce_graph_module(
+        self, gm: torch.fx.GraphModule
+    ) -> Tuple[Any, Tuple[Dict[str, Any], str]]:
+        """
+        Custom reducer for graph module to handle irrelevant data for user
+        defined triton kernels
+        Essentially what we are doing here is a huge hack where user defined
+        triton kernel contain a dynamo time side table and the arguments to the
+        call_function are indicies into this side table. These arguments are not
+        for hashing purposes since we included the source code into the cache
+        key and the numbers are prone to give false negatives due to ordering.
+        """
+        fn, (data, imports) = gm.__reduce__()
+        code = data["_code"]
+        code = re.sub(r"kernel_idx = \d+", "", code)
+        code = re.sub(r"constant_args_idx = \d+", "", code)
+        data["_code"] = code
+        return fn, (data, imports)
+
     def dumps(self, obj: Any) -> bytes:
         """
         Pickle an object and return a byte string.
@@ -775,6 +805,35 @@ def __init__(
                 else:
                     self.fx_kwargs[k] = v
 
+        from torch._higher_order_ops.triton_kernel_wrap import (
+            triton_kernel_wrapper_functional,
+            triton_kernel_wrapper_mutation,
+        )
+
+        # Node meta will not be part of gm's reduce function, so lets remember
+        # the kernel source code separately
+        self.user_defined_triton_source: List[Any] = []
+        if gm is not None:
+            for module in gm.modules():
+                if not isinstance(module, torch.fx.GraphModule):
+                    continue
+                for node in itertools.chain(
+                    module.graph.find_nodes(
+                        op="call_function", target=triton_kernel_wrapper_functional
+                    ),
+                    module.graph.find_nodes(
+                        op="call_function", target=triton_kernel_wrapper_mutation
+                    ),
+                ):
+                    data = node.meta.get(
+                        "user_defined_triton_kernel_source_and_constant_args", None
+                    )
+                    if data is None:
+                        raise AssertionError(
+                            "TritonKernelWrapper does not contain source code meta"
+                        )
+                    self.user_defined_triton_source.append(data)
+
         # Alignment checks
         self.inputs_to_check = inputs_to_check
 
@@ -833,7 +892,10 @@ def compiled_fx_graph_hash(
     include_non_inlined = not has_frozen_params(gm)
 
     details = FxGraphHashDetails(gm, example_inputs, fx_kwargs, inputs_to_check)
-    pickler = FxGraphCachePickler(include_non_inlined)
+    has_user_defined_triton_kernels = len(details.user_defined_triton_source) != 0
+    pickler = FxGraphCachePickler(
+        gm, include_non_inlined, has_user_defined_triton_kernels
+    )
     # The prefix distinguishes among the other kinds of objects we
     # cache in this module.
     key = "f" + pickler.get_hash(details)

torch/_inductor/codegen/wrapper.py

@@ -241,7 +241,7 @@ def writeline(line: str, example_grid: Optional[str] = None):
 def user_defined_triton_kernel_transitive_closure_source_code(kernel) -> str:
     """
     Given a triton kernel function pointer collect the transitive closure of
-    its dependancies
+    its dependencies
     """
     compile_wrapper = IndentedBuffer()
     compile_wrapper.splice(kernel.src, strip=True)