Add cpu_relax() helper in preparation for supporting
read_poll_timeout().

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 | 13 +++++++++++++
 4 files changed, 23 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..d1db85b76243
--- /dev/null
+++ b/rust/kernel/processor.rs
@@ -0,0 +1,13 @@
+// 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.
+pub fn cpu_relax() {
+    // SAFETY: Always safe to call.
+    unsafe { bindings::cpu_relax() }
+}
-- 
2.43.0

"FUJITA Tomonori" <fujita.tomonori@gmail.com> writes:

> Add cpu_relax() helper in preparation for supporting
> read_poll_timeout().
>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>

Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>


Best regards,
Andreas Hindborg

On Mon, Aug 11, 2025 at 01:10:37PM +0900, FUJITA Tomonori wrote:
> Add cpu_relax() helper in preparation for supporting
> read_poll_timeout().
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> +pub fn cpu_relax() {
> +    // SAFETY: Always safe to call.
> +    unsafe { bindings::cpu_relax() }
> +}

Let's mark this #[inline].

Alice

On Mon, 11 Aug 2025 09:39:36 +0000
Alice Ryhl <aliceryhl@google.com> wrote:

> On Mon, Aug 11, 2025 at 01:10:37PM +0900, FUJITA Tomonori wrote:
>> Add cpu_relax() helper in preparation for supporting
>> read_poll_timeout().
>> 
>> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> 
>> +pub fn cpu_relax() {
>> +    // SAFETY: Always safe to call.
>> +    unsafe { bindings::cpu_relax() }
>> +}
> 
> Let's mark this #[inline].

Thanks, I'll do in the next version.