netdev - Re: [PATCH 0/5] Rust abstractions for network device drivers

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Date: Tue, 20 Jun 2023 20:09:58 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Emilio Cobos Álvarez <emilio@...sal.io>, 
	Andreas Hindborg <nmi@...aspace.dk>
Cc: Andrew Lunn <andrew@...n.ch>, FUJITA Tomonori <fujita.tomonori@...il.com>, kuba@...nel.org, 
	netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, aliceryhl@...gle.com
Subject: Re: [PATCH 0/5] Rust abstractions for network device drivers

On Mon, Jun 19, 2023 at 1:27 PM Emilio Cobos Álvarez <emilio@...sal.io> wrote:
>
> Hi Andrew, Miguel,
>
> On 6/16/23 16:43, Andrew Lunn wrote:
> > I said in another email, i don't want to suggest premature
> > optimisation, before profiling is done. But in C, these functions are
> > inline for a reason. We don't want the cost of a subroutine call. We
> > want the compiler to be able to inline the code, and the optimiser to
> > be able to see it and generate the best code it can.
> >
> > Can the rust compile inline the binding including the FFI call?
>
> This is possible, with cross-language LTO, see:
>
>    https://blog.llvm.org/2019/09/closing-gap-cross-language-lto-between.html
>
> There are some requirements that need to happen for that to work
> (mainly, I believe, that the LLVM version used by rustc and clang agree).
>
> But in general it is possible. We use it extensively on Firefox. Of
> course the requirements of Firefox and the kernel might be different.
>
> I think we rely heavily on PGO instrumentation to make the linker inline
> ffi functions, but there might be other ways of forcing the linker to
> inline particular calls that bindgen could generate or what not.

Thanks Emilio! It is nice to hear cross-language LTO is working well
for Firefox.

Andreas took a look at cross-language LTO some weeks ago, if I
remember correctly (Cc'd).

I am not sure about the latest status on kernel PGO, though.

Cheers,
Miguel