Split & remove extension_parallel (#8983)

As per plan in #8932, we want to be able to include thread_parallel.h to build
libraries that are capable of parallelization, but don't require it. So, we
move the header to ExecuTorch core and add a fallback implementation (with
tests!) of parallel_for that just does a regular for loop. Then, targets
that link extension_threadpool will get parallelization automagically.

This PR doesn't add any optionally-parallelized code; that will be in the next
PR.

Author: swolchok

.lintrunner.toml

@@ -218,6 +218,8 @@ exclude_patterns = [
     'examples/**',
     'extension/**',
     'kernels/optimized/**',
+    # Justified <functional> include.
+    'runtime/kernel/thread_parallel_interface.h',
     'scripts/**',
     'third-party/**',
     'util/**',

CMakeLists.txt

@@ -751,7 +751,6 @@ if(EXECUTORCH_BUILD_PTHREADPOOL
    AND EXECUTORCH_BUILD_CPUINFO
 )
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/extension/threadpool)
-  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/extension/parallel)
 endif()
 
 if(EXECUTORCH_BUILD_PYBIND)

Test.cmake

@@ -13,7 +13,6 @@ if(BUILD_TESTING)
   add_subdirectory(extension/evalue_util/test)
   add_subdirectory(extension/kernel_util/test)
   add_subdirectory(extension/memory_allocator/test)
-  add_subdirectory(extension/parallel/test)
   add_subdirectory(extension/pytree/test)
   add_subdirectory(kernels/portable/cpu/util/test)
   add_subdirectory(kernels/prim_ops/test)

build/cmake_deps.toml

@@ -88,7 +88,6 @@ excludes = [
 deps = [
   "executorch",
   "executorch_core",
-  "extension_parallel",
   "extension_threadpool",
   "portable_kernels",
 ]
@@ -131,7 +130,7 @@ excludes = [
 deps = [
   "executorch_core",
   "executorch",
-  "extension_parallel",
+  "extension_threadpool",
 ]
 
 [targets.optimized_native_cpu_ops]
@@ -146,7 +145,6 @@ excludes = [
 deps = [
   "executorch_core",
   "executorch",
-  "extension_parallel",
   "extension_threadpool",
   "portable_kernels",
 ]
@@ -227,19 +225,6 @@ deps = [
   "extension_runner_util",
 ]
 
-[targets.extension_parallel]
-buck_targets = [
-  "//extension/parallel:thread_parallel",
-]
-filters = [
-  ".cpp$",
-]
-deps = [
-  "executorch",
-  "executorch_core",
-  "extension_threadpool",
-]
-
 [targets.extension_tensor]
 buck_targets = [
   "//extension/tensor:tensor",
@@ -379,6 +364,7 @@ excludes = [
 deps = [
   "executorch",
   "executorch_core",
+  "extension_threadpool",
   "xnnpack_backend",
   "portable_kernels",
 ]
@@ -393,6 +379,7 @@ filters = [
 deps = [
   "executorch",
   "executorch_core",
+  "extension_threadpool",
 ]
 
 [targets.xnnpack_schema]
@@ -427,7 +414,6 @@ deps = [
   "executorch",
   "executorch_core",
   "optimized_kernels",
-  "extension_parallel",
   "extension_threadpool",
   "reduce_util",
   "xnnpack_backend",
@@ -465,7 +451,7 @@ deps = [
   "executorch_core",
   "extension_data_loader",
   "extension_module",
-  "extension_parallel",
+  "extension_threadpool",
   "portable_kernels",
   "quantized_kernels",
   "xnnpack_backend",

build/executorch-config.cmake

@@ -75,7 +75,6 @@ set(lib_list
     custom_ops
     extension_module
     extension_module_static
-    extension_parallel
     extension_runner_util
     extension_tensor
     extension_threadpool
@@ -131,14 +130,9 @@ endforeach()
 
 # TODO: investigate use of install(EXPORT) to cleanly handle
 # target_compile_options/target_compile_definitions for everything.
-if(TARGET extension_parallel)
-  set_target_properties(
-    extension_parallel PROPERTIES INTERFACE_LINK_LIBRARIES extension_threadpool
-  )
-endif()
 if(TARGET cpublas)
   set_target_properties(
-    cpublas PROPERTIES INTERFACE_LINK_LIBRARIES extension_parallel
+    cpublas PROPERTIES INTERFACE_LINK_LIBRARIES extension_threadpool
   )
 endif()
 if(TARGET extension_threadpool)

extension/llm/custom_ops/op_sdpa.cpp

@@ -19,8 +19,8 @@
 #include <vector>
 
 #ifdef ET_USE_THREADPOOL
-#include <executorch/extension/parallel/thread_parallel.h>
 #include <executorch/extension/threadpool/threadpool.h>
+#include <executorch/runtime/kernel/thread_parallel_interface.h>
 #endif
 #include <executorch/extension/kernel_util/make_boxed_from_unboxed_functor.h>
 

extension/llm/custom_ops/targets.bzl

@@ -37,7 +37,6 @@ def define_common_targets():
                 "//executorch/kernels/optimized:libblas{}".format(mkl_dep),
                 "//executorch/kernels/optimized:libvec",
                 "//executorch/extension/kernel_util:kernel_util",
-                "//executorch/extension/parallel:thread_parallel",
                 "//executorch/extension/threadpool:threadpool",
             ],
             deps = [