How to record extension host performance in code-server?

[chouzz]

In the desktop version of VSCode, you can record the extension host process to analyze performance issues via the context menu. This is really useful for identifying low-performance extensions or functions based on the results. However, in code-server, there isn't a similar command, and even when trying to record performance in Chrome DevTools, it seems that it doesn't capture useful information like the desktop version does.

• context menu to record extension host performance in vscode desktop version.
  

• You can found performance issue related to spawnSync or execSync.
  

• But if you tried record performance in code-server, it's very different compared to the command. In fact, you can't find any useful information in the extension host workers; there are no functions that come from extensions.
  

[code-asher]

The web version of VS Code has an extension host that runs on the server and an extension host that runs in a web worker. Only the web worker extension host would show up in Chrome's profiler, and only web extensions can run there (and most extensions are not web extensions, I believe).

As for why that context menu option is not available, you might have better luck asking upstream in https://github.com/microsoft/vscode about this feature for the web version. I can only vaguely guess that this is something that worked in Electron that they have not been able to port to Node or web yet.

[chouzz]

So, in code-server, the extension host actually running in Linux, it's why Chrome Devtools can't record it. BTW, do you know of any other ways to analyze performance issues in extension host processes? @code-asher

[code-asher]

Yup exactly right.

I think it would be possible to use the Node profiler. For example I just tried:

$ node --prof /path/to/code-server --auth none

Then you can check the processes and find the pid of the extension host. In my case, 71247.

$ ps -eFjH | grep node
coder      69704    4075   69704    4075  0 200059 69424  9 20:42 pts/0    00:00:02       node --prof /home/coder/.local/lib/code-server-4.22.1 --port 3000
coder      69757   69704   69704    4075  0 289566 126844 2 20:42 pts/0    00:00:26         /nix/store/zsdfz83ilpz26gm44r0fh7h5bqabc4cf-nodejs-18.20.2/bin/node --prof /home/coder/.local/lib/code-server-4.22.1/out/node/entry
coder      71050   69757   69704    4075  0 231682 59456 20 20:43 pts/0    00:00:06           /nix/store/zsdfz83ilpz26gm44r0fh7h5bqabc4cf-nodejs-18.20.2/bin/node --prof /home/coder/.local/lib/code-server-4.22.1/lib/vscode/out/bootstrap-fork --type=fileWatcher
coder      71247   69757   69704    4075  0 2891821 143640 19 20:43 pts/0  00:00:17           /nix/store/zsdfz83ilpz26gm44r0fh7h5bqabc4cf-nodejs-18.20.2/bin/node --dns-result-order=ipv4first --prof /home/coder/.local/lib/code-server-4.22.1/lib/vscode/out/bootstrap-fork --type=extensionHost --transformURIs --useHostProxy=false
coder      75121   69757   69704    4075  0 181567 57876  1 20:45 pts/0    00:00:01           /nix/store/zsdfz83ilpz26gm44r0fh7h5bqabc4cf-nodejs-18.20.2/bin/node --prof /home/coder/.local/lib/code-server-4.22.1/lib/vscode/out/bootstrap-fork --type=ptyHost --logsPath /home/coder/.local/share/code-server/logs/20240606T204302

And then process the isolate file:

node --prof-process isolate-*-71247-v8.log

I am not sure how easy it is to use the results though.