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[v3,1/4] rust: sync: add `CondVar::notify_sync`

Message ID 20240104-rb-new-condvar-methods-v3-1-70b514fcbe52@google.com
State New
Headers
Series Additional CondVar methods needed by Rust Binder |

Commit Message

Alice Ryhl Jan. 4, 2024, 2:02 p.m. UTC 
  Wake up another thread synchronously.

This method behaves like `notify_one`, except that it hints to the
scheduler that the current thread is about to go to sleep, so it should
schedule the target thread on the same CPU.

This is used by Rust Binder as a performance optimization. When sending
a transaction to a different process, we usually know which thread will
handle it, so we can schedule that thread for execution next on this
CPU for better cache locality.

Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Tiago Lam <tiagolam@gmail.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/kernel/sync/condvar.rs | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Boqun Feng Jan. 4, 2024, 6:56 p.m. UTC | #1 
On Thu, Jan 04, 2024 at 02:02:41PM +0000, Alice Ryhl wrote:
> Wake up another thread synchronously.
> 
> This method behaves like `notify_one`, except that it hints to the
> scheduler that the current thread is about to go to sleep, so it should
> schedule the target thread on the same CPU.
> 
> This is used by Rust Binder as a performance optimization. When sending
> a transaction to a different process, we usually know which thread will
> handle it, so we can schedule that thread for execution next on this
> CPU for better cache locality.
> 
> Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> Reviewed-by: Tiago Lam <tiagolam@gmail.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/kernel/sync/condvar.rs | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
> index f65e19d5a37c..1a3f7b8e03dc 100644
> --- a/rust/kernel/sync/condvar.rs
> +++ b/rust/kernel/sync/condvar.rs
> @@ -155,6 +155,12 @@ fn notify(&self, count: i32, flags: u32) {
>          };
>      }
>  
> +    /// Calls the kernel function to notify one thread synchronously.

I feel like "synchronously" needs some explanation here (e.g. using the
same description in the commit log), but let's see if other future users
really need this ;-)

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> +    pub fn notify_sync(&self) {
> +        // SAFETY: `wait_list` points to valid memory.
> +        unsafe { bindings::__wake_up_sync(self.wait_list.get(), bindings::TASK_NORMAL) };
> +    }
> +
>      /// Wakes a single waiter up, if any.
>      ///
>      /// This is not 'sticky' in the sense that if no thread is waiting, the notification is lost
> 
> -- 
> 2.43.0.472.g3155946c3a-goog
>
diff mbox series

Patch

diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index f65e19d5a37c..1a3f7b8e03dc 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -155,6 +155,12 @@  fn notify(&self, count: i32, flags: u32) {
         };
     }
 
+    /// Calls the kernel function to notify one thread synchronously.
+    pub fn notify_sync(&self) {
+        // SAFETY: `wait_list` points to valid memory.
+        unsafe { bindings::__wake_up_sync(self.wait_list.get(), bindings::TASK_NORMAL) };
+    }
+
     /// Wakes a single waiter up, if any.
     ///
     /// This is not 'sticky' in the sense that if no thread is waiting, the notification is lost