[Bug 281765] llvm - ThinLTO never uses more than a single thread by default

From: <bugzilla-noreply_at_freebsd.org>
Date: Mon, 07 Oct 2024 09:00:58 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=281765

David Chisnall <theraven@FreeBSD.org> changed:

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--- Comment #3 from David Chisnall <theraven@FreeBSD.org> ---
(In reply to Dimitry Andric from comment #2)

> The reason for this was that lld was using way too many threads on many-core machines: nowadays just creating "hw.ncpu" threads is no longer a good default.

I don't believe this is true (unless RAM is not properly scaled with core
count).  The problem is build systems that try to parallelise link jobs. 
Building LLVM with PARALLEL_LINK_JOBS=1, the upstream default remains the right
one.  Building FreeBSD, it is not.  

The fix for this in the bmake system is probably to wrap lld in a shell script
that acquires a lock, invokes lld, and then releases the lock and exits with
lld's exit code.

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