From: Uros Bizjak Date: Fri, 12 Apr 2024 08:38:53 +0000 (+0200) Subject: locking/pvqspinlock/x86: Remove redundant CMP after CMPXCHG in __raw_callee_save___pv... X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=91095666125a666c8f20c2323b742c53165c0325;p=linux.git locking/pvqspinlock/x86: Remove redundant CMP after CMPXCHG in __raw_callee_save___pv_queued_spin_unlock() x86 CMPXCHG instruction returns success in the ZF flag. Remove redundant CMP instruction after CMPXCHG that performs the same check. Also update the function comment to mention the modern version of the equivalent C code. Signed-off-by: Uros Bizjak Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/20240412083908.282802-1-ubizjak@gmail.com --- diff --git a/arch/x86/include/asm/qspinlock_paravirt.h b/arch/x86/include/asm/qspinlock_paravirt.h index ef9697f20129a..466af57b8ed6a 100644 --- a/arch/x86/include/asm/qspinlock_paravirt.h +++ b/arch/x86/include/asm/qspinlock_paravirt.h @@ -25,9 +25,9 @@ __PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath, ".spinlock.text"); * * void __lockfunc __pv_queued_spin_unlock(struct qspinlock *lock) * { - * u8 lockval = cmpxchg(&lock->locked, _Q_LOCKED_VAL, 0); + * u8 lockval = _Q_LOCKED_VAL; * - * if (likely(lockval == _Q_LOCKED_VAL)) + * if (try_cmpxchg(&lock->locked, &lockval, 0)) * return; * pv_queued_spin_unlock_slowpath(lock, lockval); * } @@ -43,7 +43,6 @@ __PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath, ".spinlock.text"); "mov $0x1,%eax\n\t" \ "xor %edx,%edx\n\t" \ LOCK_PREFIX "cmpxchg %dl,(%rdi)\n\t" \ - "cmp $0x1,%al\n\t" \ "jne .slowpath\n\t" \ "pop %rdx\n\t" \ FRAME_END \