linux-kernel - Re: [PATCH v2 1/2] rust: Add cpu

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Message-ID: <CALC8CXfKPBc=axfyre8UTwO1uV=-P-u_atR5FVYG0UXszE41Xg@mail.gmail.com>
Date: Thu, 2 Oct 2025 12:33:42 -0400
From: ChaosEsque Team <chaosesqueteam@...il.com>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: a.hindborg@...nel.org, alex.gaynor@...il.com, ojeda@...nel.org, 
	aliceryhl@...gle.com, anna-maria@...utronix.de, bjorn3_gh@...tonmail.com, 
	boqun.feng@...il.com, dakr@...nel.org, frederic@...nel.org, gary@...yguo.net, 
	jstultz@...gle.com, linux-kernel@...r.kernel.org, lossin@...nel.org, 
	lyude@...hat.com, rust-for-linux@...r.kernel.org, sboyd@...nel.org, 
	tglx@...utronix.de, tmgross@...ch.edu, acourbot@...dia.com, 
	daniel.almeida@...labora.com
Subject: Re: [PATCH v2 1/2] rust: Add cpu_relax() helper

Imagine a Japanese typewriter. Couldn't be done.

On Sun, Aug 17, 2025 at 12:49 AM FUJITA Tomonori
<fujita.tomonori@...il.com> wrote:
>
> Add cpu_relax() helper in preparation for supporting
> read_poll_timeout().
>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
> ---
>  rust/helpers/helpers.c   |  1 +
>  rust/helpers/processor.c |  8 ++++++++
>  rust/kernel/lib.rs       |  1 +
>  rust/kernel/processor.rs | 14 ++++++++++++++
>  4 files changed, 24 insertions(+)
>  create mode 100644 rust/helpers/processor.c
>  create mode 100644 rust/kernel/processor.rs
>
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index 7cf7fe95e41d..04598665e7c8 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -34,6 +34,7 @@
>  #include "pid_namespace.c"
>  #include "platform.c"
>  #include "poll.c"
> +#include "processor.c"
>  #include "property.c"
>  #include "rbtree.c"
>  #include "rcu.c"
> diff --git a/rust/helpers/processor.c b/rust/helpers/processor.c
> new file mode 100644
> index 000000000000..d41355e14d6e
> --- /dev/null
> +++ b/rust/helpers/processor.c
> @@ -0,0 +1,8 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/processor.h>
> +
> +void rust_helper_cpu_relax(void)
> +{
> +       cpu_relax();
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index ed53169e795c..c098c47c1817 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -110,6 +110,7 @@
>  pub mod platform;
>  pub mod prelude;
>  pub mod print;
> +pub mod processor;
>  pub mod rbtree;
>  pub mod regulator;
>  pub mod revocable;
> diff --git a/rust/kernel/processor.rs b/rust/kernel/processor.rs
> new file mode 100644
> index 000000000000..85b49b3614dd
> --- /dev/null
> +++ b/rust/kernel/processor.rs
> @@ -0,0 +1,14 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Processor related primitives.
> +//!
> +//! C header: [`include/linux/processor.h`](srctree/include/linux/processor.h)
> +
> +/// Lower CPU power consumption or yield to a hyperthreaded twin processor.
> +///
> +/// It also happens to serve as a compiler barrier.
> +#[inline]
> +pub fn cpu_relax() {
> +    // SAFETY: Always safe to call.
> +    unsafe { bindings::cpu_relax() }
> +}
> --
> 2.43.0
>
>