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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Fri, 18 Dec 2020 04:31:36 +0100
Message-ID: <CANiq72=rFzxMyxDNkobdnMZohT_qT0KfGCincYBteyoJbtr2Gw@mail.gmail.com>
Subject: Re: Linux kernel in-tree Rust support
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Josh Triplett <josh@joshtriplett.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Geoffrey Thomas <geofft@ldpreload.com>, jbaublitz@redhat.com,
        Masahiro Yamada <masahiroy@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kees Cook <keescook@chromium.org>
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On Thu, Dec 17, 2020 at 10:45 PM Pavel Machek <pavel@ucw.cz> wrote:
>
> Well.. not everyone has 32 cores in their notebook.

It is true that complex Rust, like complex C++, does have high
compilation times. But it all depends on how much one relies on
certain language features. Straightforward Rust code is quick to
compile.

For reference, some quick stats :-)

On a given machine, building v5.10 with a minimal config under -j3
takes 3 minutes. With Rust support enabled and 4 trivial Rust modules,
it takes 50 seconds more. "A big increase!", you may indeed claim, but
those 50 seconds are basically all spent on the shared Rust support.
The actual Rust modules compile very quickly afterwards. For example,
touching either `drivers/char/mem.c` or one of the trivial Rust
modules takes the same time in that machine: 10 seconds.

This is for a minimal config -- when you start dealing with
`allmodconfig` builds, or when you start having a hundred Rust modules
instead of 4, the upfront cost becomes very small per Rust module.

> Okay. I did some refactoring recently and I really wished kernel was
> in Rust (and not in C)... so lets see what happens.

Indeed, I think it is definitely worth it.

Cheers,
Miguel