locking/qspinlock: Use atomic_try_cmpxchg_relaxed() in xchg_tail()

Use atomic_try_cmpxchg_relaxed(*ptr, &old, new) instead of
atomic_cmpxchg_relaxed (*ptr, old, new) == old in xchg_tail().

x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after CMPXCHG.

No functional change intended.

Since this code requires NR_CPUS >= 16k, I have tested it
by unconditionally setting _Q_PENDING_BITS to 1 in
<asm-generic/qspinlock_types.h>.

Signed-off-by: Uros Bizjak <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

0 files changed, 0 insertions, 0 deletions