Cargo installing multiple bin crates doesn't build them in parallel

[the8472]

Describe the problem you are trying to solve

When installing multiple bin crates, such as suggested by the rustc-dev-guide build instructions they are built sequentially. This doesn't fully utilize available parallelism on many-core systems and thus leads to longer build times than necessary.

Describe the solution you'd like

It would be nice if the binaries could be built in parallel under a shared jobserver to reduce wall-time for the install command.

[nipunn1313]

@rustbot claim

[nipunn1313]

I put up #9793 as a step in the right direction, however I was unable to figure out how to actually parallelize the install command.

I tried naively using rayon to parallelize, but the Package struct was not Sized and I was unable to proceed with that strategy. It seemed that potentially cargo was not built to have multiple cargo commands running in parallel - and some more work might be necessary to make things work - to share job pool across multiple cargo compile commands issued by cargo itself.

[nipunn1313]

@rustbot release-assignment

[skull-squadron]

Please make this happen. I have 90+ cores sitting idle during tool install builds and it takes forever. 🙏

[weihanglo]

Just got an idea as a workaround.

Since Cargo honors GNU make jobserver, We can do tricks with the combos of parallel and make:

# Makefile
all:
        +parallel cargo install ::: cli1 cli2 cli3 cli4 cli5 cli6 cli7 cli8...

Then run make -j$(getconf _NPROCESSORS_ONLN).

By doing so, the number of rustc invocations can be controlled by jobserver. OTOH, GNU parallel works as a scheduler to coordinate which binary to install next. You might also tweak -j for parallel to control the parallelism.