linux-kernel - Re: [PATCH] rust: sync: optimize rust symbol generation for CondVar

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Message-ID: <Z-BL_DFA3afcRYGE@Mac.home>
Date: Sun, 23 Mar 2025 10:59:24 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Kunwu Chan <kunwu.chan@...ux.dev>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu,
	dakr@...nel.org, nathan@...nel.org, nick.desaulniers+lkml@...il.com,
	morbo@...gle.com, justinstitt@...gle.com,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, Kunwu Chan <kunwu.chan@...mail.com>,
	Grace Deng <Grace.Deng006@...il.com>
Subject: Re: [PATCH] rust: sync: optimize rust symbol generation for CondVar

On Mon, Mar 17, 2025 at 04:13:50PM +0800, Kunwu Chan wrote:
> From: Kunwu Chan <kunwu.chan@...mail.com>
> 
> When build the kernel using the llvm-18.1.3-rust-1.85.0-x86_64
> with ARCH=arm64, the following symbols are generated:
> 
> $nm vmlinux | grep ' _R'.*CondVar | rustfilt
> ... T <kernel::sync::condvar::CondVar>::notify_all
> ... T <kernel::sync::condvar::CondVar>::notify_one
> ... T <kernel::sync::condvar::CondVar>::notify_sync
> ... T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
> ... T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
> ... T <kernel::sync::poll::PollCondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
> ... T <kernel::sync::poll::PollCondVar as core::ops::drop::Drop>::drop
> 
> These notify* symbols are trivial wrappers around the C functions
> __wake_up and __wake_up_sync.
> It doesn't make sense to go through a trivial wrapper for these
> functions, so mark them inline.
> 
> Link: https://github.com/Rust-for-Linux/linux/issues/1145
> Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
> Co-developed-by: Grace Deng <Grace.Deng006@...il.com>
> Signed-off-by: Grace Deng <Grace.Deng006@...il.com>
> Signed-off-by: Kunwu Chan <kunwu.chan@...mail.com>
> ---
>  rust/kernel/sync/condvar.rs | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
> index 7df565038d7d..a826896ba3f0 100644
> --- a/rust/kernel/sync/condvar.rs
> +++ b/rust/kernel/sync/condvar.rs
> @@ -181,6 +181,7 @@ pub fn wait_interruptible_timeout<T: ?Sized, B: Backend>(
>      }
>  
>      /// Calls the kernel function to notify the appropriate number of threads.
> +    #[inline]
>      fn notify(&self, count: c_int) {

Hmm.. I think CondVar::notify() gets inlined even without this
`#[inline]` attribute, do we need this actually?

Regards,
Boqun

>          // SAFETY: `wait_queue_head` points to valid memory.
>          unsafe {
[...]