Why the target is x86_64-unknown-linux-musl?

[ghost]

Looks like the target is x86_64 archtecture. Could you explain on why the target is x86_64 archtecture?

Thanks!

[davidbarsky]

(Moved this to discussions instead of an issue).

Assuming that you're asking why we're using x86_64-unknown-linux-musl instead of x86_64-unknown-linux-gnu, it's because the provided environment had a glibc that's too old for Rust. Statically linking the musl libc is a good way to get around that.

With the launch of the provided.al2 environment, the glibc is recent enough for Rust, which means that if folks are targeting provided.al2, then they can use x86_64-unknown-linux-gnu as a target instead.

[davidbarsky]

I can use x86_64-unknown-linux-gnu as a target instead, if set the runtime to provide.al2. Right?

That's correct.

[seanpianka]

Is there any major differences in performance, behavior, or something else between musl and gnu?

[davidbarsky]

Before taking my advice, please run your own benchmarks. It's possible that my advice is out-of-date!

---

For some time, (and this still might be the case) musl's default allocator didn't perform well with idiomatic Rust code that made many small allocations across several threads. I strongly suspect that's why customers found the cold-start times of this runtime to be slow. To mitigate this issue, I suggest that that customers should use an allocator like jemalloc or mimalloc when writing any server-side (Lambda or otherwise) Rust code that uses the x86_64-unknown-linux-musl target.

With the x86_64-unknown-linux-gnu target, I believe that the allocation issue that afflicts musl-using Rust code is significantly less pronounced (see mimalloc's benchmark suite https://github.com/microsoft/mimalloc#benchmark-results-on-a-16-core-amd-5950x-zen3). However, I still think it's worthwhile trying out alternative allocators if you have any qualms.

In terms of the build/packing experience, I think that the two are largely the same.

[goshoo]

I found this blog post.

https://andygrove.io/2020/05/why-musl-extremely-slow/

[nk9]

Lots of info in this blog post about the default musl allocator w.r.t. Rust.