Very slow performance when using Remote - WSL

[ahmedkrmn]

Type: LanguageService

Describe the bug

• OS and Version: Windows_NT 10.0.18363
• VS Code Version: 1.45.1
• C/C++ Extension Version: 0.28.1
  I tried downgrading to previous versions but the issue still persists.
• Does this issue involve using SSH remote to run the extension on a remote machine?: Yes

Description:
Code intellisense as well as auto formatting are very slow for very simple C++ files when using the Remote - WSL extension for C++ development on WSL.

uname -r output:
4.4.0-18362-Microsoft

This issue isn't there when developing on Windows.

Steps to reproduce

Create a hello world C++ file and allow formatting on save from VScode.

[Colengms]

Hi @ahmedkrmn . When remoting, the extension runs on the target machine. Are you remoting into a slow system, such as an embedded device?

Regarding the performance of formatting; The C/C++ Extension currently uses clang-format for formatting. A copy of clang-format is bundled with the extension, but a version installed on the (remote) device will be used instead if newer. You might try running clang-format directly, on the device, to see if that time is being spent by it. If so, perhaps there is a version of clang-format available that is optimized for your system. If clang-format actually completes very quickly when run directly, let us know. That might point to another issue.

[ahmedkrmn]

Hi @Colengms,
The target machine is an Ubuntu WSL version 4.4.0-18362-Microsoft.
I tried directly using clang-format as suggested and it formatted without any delays.

I did some further inspections and it appears that the issue is only preset when the workspace is the home directory of the WSL. When I created a new directory and used the VS remote extension to use it as the workspace, the issue disappears and formatting as well as linting is working well.

[sean-mcmanus]

I'm not reproing the issue. Is this with the "/home/" directory? It sounds like something is blocking our main input thread.

[MitchTalmadge]

I am having the same issues although my workspace is not the home directory. Autoformatting is very slow. How can I help provide info for debugging?

• OS and Version:
  • Host: Windows 10 v2004
  • WSL: Debian 9 stretch
• VS Code Version: 1.46.1
• C/C++ Extension Version: 0.28.3

[sean-mcmanus]

@MitchTalmadge Are your files under /mnt? I think /mnt access can be slow with WSL2.

If you can wait for CPU usage to drop to 0 before doing a format, that would help isolate if the formatting is slow or just being blocked by previous processing (formatting is not expected to be slow, so probably other operations are blocking the formatting).

[MitchTalmadge]

@MitchTalmadge Are your files under /mnt? I think /mnt access can be slow with WSL2.

If you can wait for CPU usage to drop to 0 before doing a format, that would help isolate if the formatting is slow or just being blocked by previous processing (formatting is not expected to be slow, so probably other operations are blocking the formatting).

They may be, I will have to double check and let you know. Thanks for the follow-up, really appreciate it

[ZijunHui]

I have a similar experience on WSL2 as well. My files are stored in /mnt/ and Intellisense is extremely slow, requiring more than 3 seconds for the results to pop up. After moving the files to ~, there is no longer a delay (or a very small one). I suspect this is due to WSL2, which has suprisingly slow access speed for /mnt/

I have a similar experience on WSL1. There's a CPU usage surge on cpptools:

I also checked debug level log, it stayed at Formatting Engine: clangFormat for a while.

I tried to use clang-format directly from a terminal, it's fast.

The intellisnese updating and file analyzing speed is also slow.

[corneliusroemer]

Same issue here. All my files are under /home, I'm using WSL:Ubuntu-20.04. Intellisense is extremely slow - not usable. I'm using it for Python.

[pierce-martin]

Same issue for me. Files are under the home directory. Versions are:

• vscode: 1.50.1
• WSL: Ubuntu 18.04
• C/C++ extension: 1.0.1 (both local and remote)

Main issue I see is tab completion is slow and go to declaration/definition doesn't work. I see cpptools CPU usage spike as well.