maxCoresPercentageToUseForBackgroundIndexing is too high by default

[MahdiBM]

Swift version

Swift 6.0.2 release

Platform

Editor

VS Code

Description

maxCoresPercentageToUseForBackgroundIndexing is set to 100% by default. I think that's too much.
I'd say let's lower it to 80/70% and anyone who wants maximum performance can increase it.
It's quite rare that something makes my M1 Macbook's fans spin ... and background indexing did achieve that.

Steps to Reproduce

Enabled background indexing on a big enough project.

Logging

No response

[ahoppen]

Synced to Apple’s issue tracker as rdar://140186846

[ahoppen]

maxCoresPercentageToUseForBackgroundIndexing is a little misleading and maybe we should remove the setting altogether. Even when setting it to 0.8, it might use all your CPU cores because background preparation invokes swift build --experimental-prepare-for-indexing and we don’t know how many cores that takes and we assume that it’s a single one.

All background activity happens with a lower priority on the OS level (high nice value, set here) unless it’s required for functionality in the current file. This should ensure that other higher priority tasks take precedence. And I think using system functionality like this is the better than trying to do process scheduling ourselves by limiting the number of cores we use.