Support cargo build --load-average / -l like GNU make

[devurandom]

Describe the problem you are trying to solve

I am trying to limit the load on my system while building Rust software.

Describe the solution you'd like

GNU make supports a make -l4 / make --load-average=4 parameter, that allows me to limit the target system load to 4 (e.g.). It would be nice, if Cargo would support the same.

[guanqun]

I did some quick googling and found this answer: https://stackoverflow.com/a/13355071 . It seems the author prefers using a -j option, and in cargo, the -j option is implemented, do you think you can use that instead to limit the load?

[devurandom]

-j does not care about the load on the system. Keep in mind that many processes can create load, not just make or cargo. Spawning many compilation tasks, where each uses -j N (or worse, unbounded -j), can bring a system to halt. -l M prevents that reasonably well.

I think the author of that answer also makes the mistake of passing an unbounded -j in combination with -l. If one passes a limit as in -j 6 -l 4, then make will spawn up to 6 processes, but only when the load does not exceed 4.

[jaccc]

it would be useful

[weihanglo]

Not aware of this issue until today! Seems like it is #8556 with a specific solution in mind

[epage]

Closing in favor of #12912 so we keep the conversation in one place.