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rust: sync: rcu: Mark Guard methods as inline

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Currently the implementation of "Guard" methods are basically wrappers
around rcu's function within kernel. Building the kernel with llvm
18.1.8 on x86_64 machine will generate the following symbols:

$ nm vmlinux | grep ' _R'.*Guard | rustfilt
ffffffff817b6c90 T <kernel::sync::rcu::Guard>::new
ffffffff817b6cb0 T <kernel::sync::rcu::Guard>::unlock
ffffffff817b6cd0 T <kernel::sync::rcu::Guard as core::ops::drop::Drop>::drop
ffffffff817b6c90 T <kernel::sync::rcu::Guard as core::default::Default>::default

These Rust symbols are basically wrappers around functions
"rcu_read_lock" and "rcu_read_unlock". Marking them as inline can
reduce the generation of these symbols, and saves the size of code
generation for 132 bytes.

$ ./scripts/bloat-o-meter vmlinux_old vmlinux_new
(Output is demangled for readability)

add/remove: 0/10 grow/shrink: 0/1 up/down: 0/-132 (-132)
Function                                     old     new   delta
rust_driver_pci::SampleDriver::probe        1041    1034      -7
kernel::sync::rcu::Guard::default             9       -      -9
kernel::sync::rcu::Guard::drop                9       -      -9
kernel::sync::rcu::read_lock                  9       -      -9
kernel::sync::rcu::Guard::unlock              9       -      -9
kernel::sync::rcu::Guard::new                 9       -      -9
__pfx__kernel::sync::rcu::Guard::default     16       -     -16
__pfx__kernel::sync::rcu::Guard::drop        16       -     -16
__pfx__kernel::sync::rcu::read_lock          16       -     -16
__pfx__kernel::sync::rcu::Guard::unlock      16       -     -16
__pfx__kernel::sync::rcu::Guard::new         16       -     -16
Total: Before=23365955, After=23365823, chg -0.00%

Link: https://github.com/Rust-for-Linux/linux/issues/1145
Signed-off-by: I Hsin Cheng <richard120310@gmail.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Charalampos Mitrodimas <charmitro@posteo.net>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
This commit is contained in:
I Hsin Cheng 2025-03-19 10:26:40 +08:00 • committed by Joel Fernandes
parent da6b85598a
commit 9520371e3d
1 changed files with 5 additions and 0 deletions
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5
rust/kernel/sync/rcu.rs
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@ -17,6 +17,7 @@ pub struct Guard(NotThreadSafe);
impl Guard {
/// Acquires the RCU read side lock and returns a guard.
#[inline]
pub fn new() -> Self {
// SAFETY: An FFI call with no additional requirements.
unsafe { bindings::rcu_read_lock() };
@ -25,16 +26,19 @@ impl Guard {
}
/// Explicitly releases the RCU read side lock.
#[inline]
pub fn unlock(self) {}
}
impl Default for Guard {
#[inline]
fn default() -> Self {
Self::new()
}
}
impl Drop for Guard {
#[inline]
fn drop(&mut self) {
// SAFETY: By the type invariants, the RCU read side is locked, so it is ok to unlock it.
unsafe { bindings::rcu_read_unlock() };
@ -42,6 +46,7 @@ impl Drop for Guard {
}
/// Acquires the RCU read side lock.
#[inline]
pub fn read_lock() -> Guard {
Guard::new()
}