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| author | Uros Bizjak <ubizjak@gmail.com> | 2024-01-24 11:49:53 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2024-03-01 13:02:05 +0100 |
| commit | ce3576ebd62d99f79c1dc98824e2ef6d6ab68434 (patch) | |
| tree | ff97be9bf28a71d1b790982c793ebbe8591c7695 /kernel/locking | |
| parent | e807c2a37044a51de89d6d4f8a1f5ecfb3752f36 (diff) | |
| download | linux-ce3576ebd62d99f79c1dc98824e2ef6d6ab68434.tar.gz linux-ce3576ebd62d99f79c1dc98824e2ef6d6ab68434.tar.bz2 linux-ce3576ebd62d99f79c1dc98824e2ef6d6ab68434.zip | |
locking/rtmutex: Use try_cmpxchg_relaxed() in mark_rt_mutex_waiters()
Use try_cmpxchg() instead of cmpxchg(*ptr, old, new) == old.
The x86 CMPXCHG instruction returns success in the ZF flag, so this change
saves a compare after CMPXCHG (and related move instruction in front of CMPXCHG).
Also, try_cmpxchg() implicitly assigns old *ptr value to "old" when CMPXCHG
fails. There is no need to re-read the value in the loop.
Note that the value from *ptr should be read using READ_ONCE() to prevent
the compiler from merging, refetching or reordering the read.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20240124104953.612063-1-ubizjak@gmail.com
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/rtmutex.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 4a10e8c16fd2..88d08eeb8bc0 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -237,12 +237,13 @@ static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock, */ static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock) { - unsigned long owner, *p = (unsigned long *) &lock->owner; + unsigned long *p = (unsigned long *) &lock->owner; + unsigned long owner, new; + owner = READ_ONCE(*p); do { - owner = *p; - } while (cmpxchg_relaxed(p, owner, - owner | RT_MUTEX_HAS_WAITERS) != owner); + new = owner | RT_MUTEX_HAS_WAITERS; + } while (!try_cmpxchg_relaxed(p, &owner, new)); /* * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE |