[PATCH v2 10/20] bit_spinlock: __always_inline (un)lock functions

David Hildenbrand
2025-02-24T16:56:39Z

The compiler might decide that it is a smart idea to not inline
bit_spin_lock(), primarily when a couple of functions in the same file end
up calling it. Especially when used in RMAP map/unmap code next, the
compiler sometimes decides to not inline, which is then observable in
some micro-benchmarks.

Let's simply flag all lock/unlock functions as __always_inline;
arch_test_and_set_bit_lock() and friends are already tagged like that
(but not test_and_set_bit_lock() for some reason).

If ever a problem, we could split it into a fast and a slow path, and
only force the fast path to be inlined. But there is nothing
particularly "big" here.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/bit_spinlock.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
index bbc4730a6505c..c0989b5b0407f 100644
--- a/include/linux/bit_spinlock.h
+++ b/include/linux/bit_spinlock.h
@@ -13,7 +13,7 @@
* Don't use this unless you really need to: spin_lock() and spin_unlock()
* are significantly faster.
*/
-static inline void bit_spin_lock(int bitnum, unsigned long *addr)
+static __always_inline void bit_spin_lock(int bitnum, unsigned long *addr)
{
/*
* Assuming the lock is uncontended, this never enters
@@ -38,7 +38,7 @@ static inline void bit_spin_lock(int bitnum, unsigned long *addr)
/*
* Return true if it was acquired
*/
-static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
+static __always_inline int bit_spin_trylock(int bitnum, unsigned long *addr)
{
preempt_disable();
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
@@ -54,7 +54,7 @@ static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
/*
* bit-based spin_unlock()
*/
-static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
+static __always_inline void bit_spin_unlock(int bitnum, unsigned long *addr)
{
#ifdef CONFIG_DEBUG_SPINLOCK
BUG_ON(!test_bit(bitnum, addr));
@@ -71,7 +71,7 @@ static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
* non-atomic version, which can be used eg. if the bit lock itself is
* protecting the rest of the flags in the word.
*/
-static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
+static __always_inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
{
#ifdef CONFIG_DEBUG_SPINLOCK
BUG_ON(!test_bit(bitnum, addr));
--
2.48.1