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| author |  Uros Bizjak <ubizjak@gmail.com>
| 2024-03-25 15:09:32 +0100 |
|---|---|---|
| committer |  Ingo Molnar <mingo@kernel.org>
| 2024-04-12 11:40:51 +0200 |
| commit | 6a97734f2222e0352f1900e3eb3167e9069b91bb (patch) | |
| tree | aeb9a451bb6965ca8c42f5f259a3aed935687624 /kernel/locking | |
| parent | locking/qspinlock: Use atomic_try_cmpxchg_relaxed() in xchg_tail() (diff) | |
| download | linux-6a97734f2222e0352f1900e3eb3167e9069b91bb.tar.gz linux-6a97734f2222e0352f1900e3eb3167e9069b91bb.tar.bz2 linux-6a97734f2222e0352f1900e3eb3167e9069b91bb.zip | |
locking/pvqspinlock: Use try_cmpxchg_acquire() in trylock_clear_pending()
Replace this pattern in trylock_clear_pending():
cmpxchg_acquire(*ptr, old, new) == old
... with the simpler and faster:
try_cmpxchg_acquire(*ptr, &old, new)
The x86 CMPXCHG instruction returns success in the ZF flag, so this change
saves a compare after the CMPXCHG.
Also change the return type of the function to bool and streamline
the control flow in the _Q_PENDING_BITS == 8 variant a bit.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240325140943.815051-1-ubizjak@gmail.com
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/qspinlock_paravirt.h | 31 |
1 files changed, 13 insertions, 18 deletions
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 169950fe1aad..77ba80bd95f9 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -116,11 +116,12 @@ static __always_inline void set_pending(struct qspinlock *lock) * barrier. Therefore, an atomic cmpxchg_acquire() is used to acquire the * lock just to be sure that it will get it. */ -static __always_inline int trylock_clear_pending(struct qspinlock *lock) +static __always_inline bool trylock_clear_pending(struct qspinlock *lock) { + u16 old = _Q_PENDING_VAL; + return !READ_ONCE(lock->locked) && - (cmpxchg_acquire(&lock->locked_pending, _Q_PENDING_VAL, - _Q_LOCKED_VAL) == _Q_PENDING_VAL); + try_cmpxchg_acquire(&lock->locked_pending, &old, _Q_LOCKED_VAL); } #else /* _Q_PENDING_BITS == 8 */ static __always_inline void set_pending(struct qspinlock *lock) @@ -128,27 +129,21 @@ static __always_inline void set_pending(struct qspinlock *lock) atomic_or(_Q_PENDING_VAL, &lock->val); } -static __always_inline int trylock_clear_pending(struct qspinlock *lock) +static __always_inline bool trylock_clear_pending(struct qspinlock *lock) { - int val = atomic_read(&lock->val); - - for (;;) { - int old, new; - - if (val & _Q_LOCKED_MASK) - break; + int old, new; + old = atomic_read(&lock->val); + do { + if (old & _Q_LOCKED_MASK) + return false; /* * Try to clear pending bit & set locked bit */ - old = val; - new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL; - val = atomic_cmpxchg_acquire(&lock->val, old, new); + new = (old & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL; + } while (!atomic_try_cmpxchg_acquire (&lock->val, &old, new)); - if (val == old) - return 1; - } - return 0; + return true; } #endif /* _Q_PENDING_BITS == 8 */ |