Graph Compiler

Intel® oneAPI Deep Neural Network Developer Guide and Reference

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ID 768875

Date 7/13/2023

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Graph Compiler

oneDNN Graph Compiler is an experimental backend for oneDNN Graph API. It can generate optimized implementations for complex computational graphs including multi-head attention (MHA), multi-layer perceptron (MLP), and convolution residual blocks over typical data types for both inference and training. It also brings improved performance by providing more flexible operator fusion.

Use of oneDNN Graph Compiler is transparent for applications, as it does not involve API or programming model changes.

Build-Time Controls

The following build time options only work when ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_BACKEND is ON.

CMake Option	Supported values (defaults in bold)	Description
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT	llvm, c, builtin	Selects the CPU codegen and JIT to be built by graph compiler backend. Multiple codegen approaches can be used simultaneously. See the example for setting multiple codegen methods.
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_LLVM_CONFIG	AUTO , path to llvm-config binary	Defines the method for detecting and configuring LLVM.

Codegen and JIT Options

Graph compiler backend supports several different codegen and JIT options including C, LLVM, and builtin (xbyak). Users can choose to build a subset of available options by setting the ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT option.

cmake .. -DONEDNN_BUILD_GRAPH=ON -DONEDNN_EXPERIMENTAL_GRAPH_COMPILER_BACKEND=ON -DONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT="c;builtin"

This will only build c and builtin codegen options.

cmake .. -DONEDNN_BUILD_GRAPH=ON -DONEDNN_EXPERIMENTAL_GRAPH_COMPILER_BACKEND=ON -DONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT="llvm;c;builtin"

This will build all three codegen options.

C codegen generates temporary cpp files and adopts g++ to compile them into the executable. It can be used for debugging purposes as the generated code is more friendly and readable to developers.

LLVM

LLVM codegen generates LLVM-IR in memory. It provides the best performance among all supported codegen methods. When LLVM codegen is chosen, extra LLVM dependency is required. If LLVM does not exist in this case, a CMake error will occur.

Users can set ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_LLVM_CONFIG to specify the LLVM to be integrated. By default, ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_LLVM_CONFIG is set to AUTO, which auto-detects existing LLVM in the environment. If auto-detection fails or user wants to explicitly specify the version of LLVM, a specific path to llvm-config binary shall be set.

Users can follow the guidelines to build and install LLVM from source, or download and install the pre-built binary from here.

NOTE:

LLVM 10.0 or above is required to enable LLVM codegen.

Builtin

Builtin codegen and JIT method is implemented with xbyak technology inside. Compared with C or LLVM codegen, it has no extra dependency.

Environment Variables

The following environment variables are introduced by the graph compiler backend.

Environment Variable	Value	Description
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT	llvm builtin c	Uses LLVM as codegen and JIT method Uses builtin as codegen and JIT method Uses C as codegen and JIT method
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_OPT_LEVEL	0 1,2, 3	Turns off optimization passes and sets the compilation optimization level to be 0 in C and LLVM JIT Sets the compilation optimization level of C and LLVM JIT
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_KERNEL_TRACE	0 1, stderr or filename.json	No kernel execution trace output Generates kernel execution trace to the file specified by the given filename with chrome tracing format
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_PRINT_PASS_RESULT	0	No IR output after each graph or tensor IR pass
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_PRINT_PASS_RESULT	1	Prints the output IR of each graph and tensor IR passes
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_VERBOSE	0 1 2	No verbose output Prints warning messages during compilation Prints warning messages and info logs (e.g. fusion-related information) during compilation
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_DUMP_GENCODE	path_to_dump	Dumps the generated kernel in C
ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_C_INCLUDE	path_to_c_codegen_header	Specifies the C codegen header for JIT compilation

Enable Tracing

ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_KERNEL_TRACE=1 ./application

This will produce a kernel execution trace in JSON format that will be stored to the default destination: ./sctrace.json.

ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_KERNEL_TRACE=1,stderr ./application

This will dump a kernel execution trace to the stderr stream.

ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_KERNEL_TRACE=1,/tmp/filename.json ./application

This will produce a kernel execution trace in JSON format that will be stored to the user specified path /tmp/filename.json.

Switch Between Different Codegen Methods

By default, codegen methods have priorities ranked from higher to lower as llvm, c, builtin. When multiple codegen and JIT methods are enabled at build stage, the method with the highest priority is adopted at runtime by default.

Users can switch to a different codegen method at runtime by setting ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT.

ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT=builtin ./application

This will switch the CPU codegen and JIT method to builtin (xbyak).

ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_CPU_JIT=c ./application

This will switch the CPU codegen and JIT method to c.

When using C codegen option, the generated C code will rely on existing runtime function declarations in cpu_include.hpp. ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_C_INCLUDE environment variable is used to specify the corresponding include path. Normally, the include path is automatically set at CMake build stage. But if the following error message occurs environment variable ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_C_INCLUDE is not set, users shall manually set ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_C_INCLUDE to /path_to_onednn_repo/src/graph/backend/graph_compiler/core/src.

WARNING:

The specified codegen method must be built. Otherwise, the default codegen method would be used.

Enable Code Dumping

Users can use ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_DUMP_GENCODE variable to generate offline C kernels.

ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_DUMP_GENCODE="./dump_code" ./application

This will dump the generated C kernels to dump_code folder.

WARNING:

ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_DUMP_GENCODE works under both LLVM and C codegen.

WARNING:

The user specified ONEDNN_EXPERIMENTAL_GRAPH_COMPILER_DUMP_GENCODE path shall be an existing folder. Otherwise the code dumping will not be in effect.

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Build-Time Controls

Environment Variables