wasmtime / issue #7732 Performance issue related to acces... · git-wasmtime

Wasmtime GitHub notifications bot (Dec 28 2023 at 14:40):

ShuyaoJiang opened issue #7732:

Summary

Hi, I ran the attached case (C program, compiled to Wasm by Emscripten) in different Wasm runtimes, and found abnormal performance in Wasmtime compared with other runtimes. The execution time of this case (time interval from the start to the end of the execution of Wasm bytecode running command) on different runtimes is as follows:

Wasmtime: 136ms
WasmEdge (AOT): 16ms
WAMR (AOT): 11ms

We found that in most other test cases, Wasmtime can achieve similar performance (1-2x) with the other two runtimes. However, in this case, Wasmtime is about 10x slower than the other two runtimes.

Emscripten

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.49 (04a0cad4d4c9f5d62876821274d78cd0a52427af)
clang version 18.0.0 (https://github.com/llvm/llvm-project 269685545e439ad050b67740533c59f965cae955)
Target: wasm32-unknown-emscripten
Thread model: posix

Wasm Runtime Version

Wasmtime: cli 15.0.0
WasmEdge: 0.13.5
WAMR: 1.2.3

Hardware & OS

CPU: Intel(R) Xeon(R) E5-2686 v4 CPU @ 2.30GHz
Memory: 16GB
OS: Ubuntu 20.04.6 LTS

Additional details

The attached source program is synthesized by a Csmith seed and a code snippet from another program. The inserted code snippet is on lines 2370-2375 of the source program, which is a loop accessing a pointer to a constant (the code snippet is attached below). So, we think that this abnormal performance may be caused by some improper handling when accessing such pointers to constant. Could you please check this situation? Thank you!

for (print_hash_value = 0; (print_hash_value > 16); ++print_hash_value)
{ /* block id: 394 */
    if ((*g_1123))
        break;
}

1702378284212.zip

Wasmtime GitHub notifications bot (Jan 02 2024 at 19:55):

Thanks for the bug report.

Similar to the other issue you filed, can you separate timing of the compilation and execution phases and let us know whether execution is still 10x slower than others?

Thanks!

Wasmtime GitHub notifications bot (Jan 25 2024 at 00:12):

I've taken a look at this locally (thanks for the report!) and I've used this script

import { readFile } from 'node:fs/promises';
import { WASI } from 'wasi';
import { argv } from 'node:process';

const wasi = new WASI({
  version: 'preview1',
  args: argv.slice(2),
});

const m = process.argv[2];
const wasm = await WebAssembly.compile(await readFile(m));
const obj = wasi.getImportObject();
obj.env = {
  memory: new WebAssembly.Memory({shared: true, initial: 8000, maximum: 16000}),
};
obj.wasi = {
  'thread-spawn': function() {
    throw new Error('wasi thread spawn');
  },
};
const instance = await WebAssembly.instantiate(wasm, obj);

const initial = performance.now();
wasi.start(instance);
console.log(performance.now() - initial);

</details>

to compare Wasmtime and node (as those were the easiest comparisons I could get on hand).

I added a little instrumentation to wasmtime run and I got Node executing this function in 1.2ms and Wasmtime was in 400us. Given that I don't think that this is related to runtime, so I would instead also be interested in what @fitzgen of seeing if the timing for Wasmtime included the compilation to native for the Wasm module.

Now that being said if Cranelift takes 100ms to compile something that LLVM compiles in 10ms that's also a bug, so still interested in this!

Last updated: Dec 23 2024 at 12:05 UTC

Stream: git-wasmtime

Topic: wasmtime / issue #7732 Performance issue related to acces...