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

[Boqun Feng]

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@xxxxxxxxx>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@xxxxxxxxx>
> Reviewed-by: Tiago Lam <tiagolam@xxxxxxxxx>
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> ---
>  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@xxxxxxxxx>

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
>