# Tune the performance of running wasm/aot file

Normally there are some methods to tune the performance:

## 1. Use `wasm-opt` tool

Download the [binaryen release](https://github.com/WebAssembly/binaryen/releases), and use the `wasm-opt` tool in it to optimize the wasm file, for example:

```bash
wasm-opt -O4 -o test_opt.wasm test.wasm
```

## 2. Enable `simd128` option when compiling wasm source files

WebAssembly [128-bit SIMD](https://github.com/WebAssembly/simd) is supported by WAMR on x86-64 and aarch64 targets, enabling it when compiling wasm source files may greatly improve the performance. For [wasi-sdk](https://github.com/WebAssembly/wasi-sdk) and [emsdk](https://github.com/emscripten-core/emsdk), please add `-msimd128` flag for `clang` and `emcc/em++`:

```bash
/opt/wasi-sdk/bin/clang -msimd128 -O3 -o <wasm_file> <c/c++ source files>

emcc -msimd128 -O3 -o <wasm_file> <c/c++ source files>
```

## 3. Enable segue optimization for wamrc when generating the aot file

[Segue](https://plas2022.github.io/files/pdf/SegueColorGuard.pdf) is an optimization technology which uses x86 segment register to store the WebAssembly linear memory base address, so as to remove most of the cost of SFI (Software-based Fault Isolation) base addition and free up a general purpose register, by this way it may:

- Improve the performance of JIT/AOT
- Reduce the footprint of JIT/AOT, the JIT/AOT code generated is smaller
- Reduce the compilation time of JIT/AOT

Currently it is supported on linux x86-64, developer can use `--enable-segue=[<flags>]` for wamrc:

```bash
wamrc --enable-segue -o aot_file wasm_file
# or
wamrc --enable-segue=[<flags>] -o aot_file wasm_file
```

`flags` can be: i32.load, i64.load, f32.load, f64.load, v128.load, i32.store, i64.store, f32.store, f64.store and v128.store, use comma to separate them, e.g. `--enable-segue=i32.load,i64.store`, and `--enable-segue` means all flags are added.

> Note: Normally for most cases, using `--enable-segue` is enough, but for some cases, using `--enable-segue=<flags>` may be better, for example for CoreMark benchmark, `--enable-segue=i32.store` may lead to better performance than `--enable-segue`.

## 4. Enable segue optimization for iwasm when running wasm file

Similar to segue optimization for wamrc, run:

```bash
iwasm --enable-segue wasm_file      (iwasm is built with llvm-jit enabled)
# or
iwasm --enable-segue=[<flags>] wasm_file
```

## 5. Use the AOT static PGO method

LLVM PGO (Profile-Guided Optimization) allows the compiler to better optimize code for how it actually runs. WAMR supports AOT static PGO, currently it is tested on Linux x86-64 and x86-32. The basic steps are:

1. Use `wamrc --enable-llvm-pgo -o <aot_file_of_pgo> <wasm_file>` to generate an instrumented aot file.

2. Compile iwasm with `cmake -DWAMR_BUILD_STATIC_PGO=1` and run `iwasm --gen-prof-file=<raw_profile_file> <aot_file_of_pgo>` to generate the raw profile file.

> Note: Directly dumping raw profile data to file system may be unsupported in some environments, developer can dump the profile data into memory buffer instead and try outputting it through network (e.g. uart or socket):

```C
uint32_t
wasm_runtime_get_pgo_prof_data_size(wasm_module_inst_t module_inst);

uint32_t
wasm_runtime_dump_pgo_prof_data_to_buf(wasm_module_inst_t module_inst, char *buf, uint32_t len);
```

3. Install or compile `llvm-profdata` tool，refer to [here](../tests/benchmarks/README.md#install-llvm-profdata) for the details.

4. Run `llvm-profdata merge -output=<profile_file> <raw_profile_file>` to merge the raw profile file into the profile file.

5. Run `wamrc --use-prof-file=<profile_file> -o <aot_file> <wasm_file>` to generate the optimized aot file.

6. Run the optimized aot_file: `iwasm <aot_file>`.

Developer can refer to the `test_pgo.sh` files under each benchmark folder for more details, e.g. [test_pgo.sh](../tests/benchmarks/coremark/test_pgo.sh) of CoreMark benchmark.

## 6. Disable the memory boundary check

Please notice that this method is not a general solution since it may lead to security issues. And only boost the performance for some platforms in AOT mode and don't support hardware trap for memory boundary check.

1. Build WAMR with `-DWAMR_CONFIGUABLE_BOUNDS_CHECKS=1` option.

2. Compile AOT module by wamrc with `--bounds-check=0` option.

3. Run the AOT module by iwasm with `--disable-bounds-checks` option.

> Note: The size of AOT file will be much smaller than the default, and some tricks are possible such as let the wasm application access the memory of host os directly.
> Please notice that if this option is enabled, the wasm spec test will fail since it requires the memory boundary check. For example, the runtime will crash when accessing the memory out of the boundary in some cases instead of throwing an exception as the spec requires.

You should only use this method for well tested wasm applications and make sure the memory access is safe.

## 7. Use linux-perf

Linux perf is a powerful tool to analyze the performance of a program, developer can use it to find the hot functions and optimize them. It is one profiler supported by WAMR. In order to use it, you need to add `--perf-profile` while running _iwasm_. By default, it is disabled.

> [!CAUTION]
> For now, only llvm-jit mode supports linux-perf.

Here is a basic example, if there is a Wasm application _foo.wasm_, you'll execute.

```
$ perf record --output=perf.data.raw -- iwasm --perf-profile foo.wasm
```

This will create a _perf.data_ and a _jit-xxx.dump_ under _~/.debug.jit/_ folder. This extra file is WAMR generated at runtime, and it contains the mapping between the JIT code and the original Wasm function names.

The next thing need to do is to merge _jit-xxx.dump_ file into the _perf.data_.

```
$ perf inject --jit --input=perf.data.raw --output=perf.data
```

This step will create a lot of _jitted-xxxx-N.so_ which are ELF images for all JIT functions created at runtime.

> [!TIP]
> add `-v` and check if there is output likes _write ELF image ..._. If yes, it means above merge is successful.

Finally, you can use _perf report_ to analyze the performance.

```
$ perf report --input=perf.data
```

> [!CAUTION]
> Using release build of llvm and iwasm will produce "[unknown]" functions in the call graph. It is not only because
> of the missing debug information, but also because of removing frame pointers. To get the complete result, please
> use debug build of llvm and iwasm.
>
> Wasm functions will not be affected.

### 7.1 Flamegraph

[Flamegraph](https://www.brendangregg.com/flamegraphs.html) is a powerful tool to visualize stack traces of profiled software so that the most frequent code-paths can be identified quickly and accurately. In order to use it, you need to record call graphs when running `perf record`

```
$ perf record -k mono --call-graph=fp --output=perf.data.raw -- iwasm --perf-profile foo.wasm
```


merge the _jit-xxx.dump_ file into the _perf.data.raw_.

```
$ perf inject --jit --input=perf.data.raw --output=perf.data
```

generate the stack trace file.

```
$ perf script > out.perf
```

[fold stacks](https://github.com/brendangregg/FlameGraph#2-fold-stacks).

```
$ ./FlameGraph/stackcollapse-perf.pl out.perf > out.folded
```

[render a flamegraph](https://github.com/brendangregg/FlameGraph#3-flamegraphpl)

```
$ ./FlameGraph/flamegraph.pl out.folded > perf.foo.wasm.svg
```