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

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Message-ID: <01c67d96-6477-4851-81ae-0cbee3b9e893@linux.dev>
Date: Mon, 24 Mar 2025 14:01:54 +0800
From: Kunwu Chan <kunwu.chan@...ux.dev>
To: Boqun Feng <boqun.feng@...il.com>
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 2025/3/24 12:23, Boqun Feng wrote:
> On Mon, Mar 24, 2025 at 10:08:29AM +0800, Kunwu Chan wrote:
>> On 2025/3/24 01:59, Boqun Feng wrote:
>>> 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?
>> Actualy, after add '#[inline]', the build result is (compilecmd is 'make
>> ARCH=arm64 LLVM=1-j8' ):
>>
>> $nm vmlinux | grep ' _R'.*CondVar | rustfilt
>> ffff800080019e90 T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_ex
>> plicit
>> ffff800080019e90 T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_ex
>> plicit
>> ffff800080019e90 T <kernel::sync::poll::PollCondVar>::new::{closure#0}::{closure#0}::panic_cold_e
>> xplicit
>> ffff8000805b8c7c T <kernel::sync::poll::PollCondVar as
>> core::ops::drop::Drop>::drop
>>
>>
>> And before add '#[inline]',the 'nm vmlinux | grep ' _R'.*CondVar | rustfilt'
>> appear 'notify' function,
>>
>> Seems like the LLVM didn't make it inline.
>>
> Your commit log said:
>
> ... 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
>
> so no *notify* symbol even before the patch, right? I also checked with

My bad,I mistakenly thought it was some other 'notify_*' functions,

it should be LLVM automatically inline 'notify', I will remove it in the 
next version.

> my local build, without your patch, there is still no symbol for
> notify().
>
> Regards,
> Boqun

-- 
Thanks,
   Kunwu.Chan(Tao.Chan)