Default to the libc backend?

[sunfishcode]

On Linux, rustix currently defaults to the linux_raw backend. Should it switch to defaulting to the libc backend?

linux_raw seemed to make sense at a time when I imagined that something in the direction of mustang/eyra/origin/origin-studio/std-ported-to-rustix/etc. would eventually become important. Or that the *-linux-none targets would want to use rustix for I/O. Or that something else would come along. But that doesn't seem to have happened.

I don't have anything immediate plans here; I'm just looking for input right now.

[notgull]

I'm aware that the linux_raw backend is, at least in theory, more performant than the libc backend. So I'd worry that if this change were to be made, a lot of downstream users would wake up to surprising performance degradations in their code.

[sunfishcode]

On a computer I happen to have handy, the getpid benchmark in the tree is about 2.5% faster with the linux_raw backend than with libc. clock_gettime is a vDSO call instead of a syscall, but here also linux_raw is about 2.5% faster on this computer.

The command to run these bencmarks is RUSTFLAGS=--cfg=criterion cargo bench --features=fs,time,process,stdio in the rustix tree.

[notgull]

Exactly; I think that this will be noticeable to downstream consumers of rustix. So my vote is "no".