Re: [PATCH v2 1/2] rust: Add cpu_relax() helper

[Daniel Almeida <daniel.almeida@collabora.com>]

> On 17 Aug 2025, at 01:47, FUJITA Tomonori <fujita.tomonori@gmail.com> wrote:
> 
> Add cpu_relax() helper in preparation for supporting
> read_poll_timeout().
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.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
> 
> 

Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>