diff options
| author | Linus Torvalds | 2024-03-11 18:33:03 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2024-03-11 18:33:03 -0700 |
| commit | a5b1a017cb76e4898dd62fcb97e8aee6a63b33b5 (patch) | |
| tree | af38e275caeceed23ec5dea73cf71aa7818da75b /arch/x86 | |
| parent | b0402403e54ae9eb94ce1cbb53c7def776e97426 (diff) | |
| parent | ce3576ebd62d99f79c1dc98824e2ef6d6ab68434 (diff) | |
Merge tag 'locking-core-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
- Micro-optimize local_xchg() and the rtmutex code on x86
- Fix percpu-rwsem contention tracepoints
- Simplify debugging Kconfig dependencies
- Update/clarify the documentation of atomic primitives
- Misc cleanups
* tag 'locking-core-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/rtmutex: Use try_cmpxchg_relaxed() in mark_rt_mutex_waiters()
locking/x86: Implement local_xchg() using CMPXCHG without the LOCK prefix
locking/percpu-rwsem: Trigger contention tracepoints only if contended
locking/rwsem: Make DEBUG_RWSEMS and PREEMPT_RT mutually exclusive
locking/rwsem: Clarify that RWSEM_READER_OWNED is just a hint
locking/mutex: Simplify <linux/mutex.h>
locking/qspinlock: Fix 'wait_early' set but not used warning
locking/atomic: scripts: Clarify ordering of conditional atomics
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/include/asm/local.h | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/arch/x86/include/asm/local.h b/arch/x86/include/asm/local.h index 73dba8b94443..59aa966dc212 100644 --- a/arch/x86/include/asm/local.h +++ b/arch/x86/include/asm/local.h @@ -131,8 +131,20 @@ static inline bool local_try_cmpxchg(local_t *l, long *old, long new) (typeof(l->a.counter) *) old, new); } -/* Always has a lock prefix */ -#define local_xchg(l, n) (xchg(&((l)->a.counter), (n))) +/* + * Implement local_xchg using CMPXCHG instruction without the LOCK prefix. + * XCHG is expensive due to the implied LOCK prefix. The processor + * cannot prefetch cachelines if XCHG is used. + */ +static __always_inline long +local_xchg(local_t *l, long n) +{ + long c = local_read(l); + + do { } while (!local_try_cmpxchg(l, &c, n)); + + return c; +} /** * local_add_unless - add unless the number is already a given value |