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| author | Will Deacon <will.deacon@arm.com> | 2018-04-26 11:34:26 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-04-27 09:48:52 +0200 |
| commit | ae75d9089ff7095d1d1a12c3cd86b21d3eaf3b15 (patch) | |
| tree | a20982c45c6d23b63e8f7debae5946b4f8604c09 /kernel/locking | |
| parent | 9d4646d14d51d62b967a12452c30ea7edf8dd8fa (diff) | |
| download | linux-0-day-ae75d9089ff7095d1d1a12c3cd86b21d3eaf3b15.tar.gz linux-0-day-ae75d9089ff7095d1d1a12c3cd86b21d3eaf3b15.tar.xz | |
locking/qspinlock: Use try_cmpxchg() instead of cmpxchg() when locking
When reaching the head of an uncontended queue on the qspinlock slow-path,
using a try_cmpxchg() instead of a cmpxchg() operation to transition the
lock work to _Q_LOCKED_VAL generates slightly better code for x86 and
pretty much identical code for arm64.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-13-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/qspinlock.c | 19 |
1 files changed, 9 insertions, 10 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 956a12983bd0a..46813185957bc 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -467,16 +467,15 @@ locked: * Otherwise, we only need to grab the lock. */ - /* In the PV case we might already have _Q_LOCKED_VAL set */ - if ((val & _Q_TAIL_MASK) == tail) { - /* - * The atomic_cond_read_acquire() call above has provided the - * necessary acquire semantics required for locking. - */ - old = atomic_cmpxchg_relaxed(&lock->val, val, _Q_LOCKED_VAL); - if (old == val) - goto release; /* No contention */ - } + /* + * In the PV case we might already have _Q_LOCKED_VAL set. + * + * The atomic_cond_read_acquire() call above has provided the + * necessary acquire semantics required for locking. + */ + if (((val & _Q_TAIL_MASK) == tail) && + atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL)) + goto release; /* No contention */ /* Either somebody is queued behind us or _Q_PENDING_VAL is set */ set_locked(lock); |