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authorPeter Zijlstra <peterz@infradead.org>2016-04-04 10:57:12 +0200
committerIngo Molnar <mingo@kernel.org>2016-06-14 11:54:27 +0200
commit1f03e8d2919270bd6ef64f39a45ce8df8a9f012a (patch)
tree0cdd5de370212a021d0a1a3439bbc4b0a77fea8b /kernel/locking
parent245050c287a9176cee9f98109df101909c1eeef4 (diff)
locking/barriers: Replace smp_cond_acquire() with smp_cond_load_acquire()
This new form allows using hardware assisted waiting. Some hardware (ARM64 and x86) allow monitoring an address for changes, so by providing a pointer we can use this to replace the cpu_relax() with hardware optimized methods in the future. Requested-by: Will Deacon <will.deacon@arm.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/qspinlock.c12
1 files changed, 6 insertions, 6 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 2f9153b183c9..1b8dda90ebfa 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -475,7 +475,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
* sequentiality; this is because not all clear_pending_set_locked()
* implementations imply full barriers.
*/
- smp_cond_acquire(!(atomic_read(&lock->val) & _Q_LOCKED_MASK));
+ smp_cond_load_acquire(&lock->val.counter, !(VAL & _Q_LOCKED_MASK));
/*
* take ownership and clear the pending bit.
@@ -562,7 +562,7 @@ queue:
*
* The PV pv_wait_head_or_lock function, if active, will acquire
* the lock and return a non-zero value. So we have to skip the
- * smp_cond_acquire() call. As the next PV queue head hasn't been
+ * smp_cond_load_acquire() call. As the next PV queue head hasn't been
* designated yet, there is no way for the locked value to become
* _Q_SLOW_VAL. So both the set_locked() and the
* atomic_cmpxchg_relaxed() calls will be safe.
@@ -573,7 +573,7 @@ queue:
if ((val = pv_wait_head_or_lock(lock, node)))
goto locked;
- smp_cond_acquire(!((val = atomic_read(&lock->val)) & _Q_LOCKED_PENDING_MASK));
+ val = smp_cond_load_acquire(&lock->val.counter, !(VAL & _Q_LOCKED_PENDING_MASK));
locked:
/*
@@ -593,9 +593,9 @@ locked:
break;
}
/*
- * The smp_cond_acquire() call above has provided the necessary
- * acquire semantics required for locking. At most two
- * iterations of this loop may be ran.
+ * The smp_cond_load_acquire() call above has provided the
+ * necessary acquire semantics required for locking. At most
+ * two iterations of this loop may be ran.
*/
old = atomic_cmpxchg_relaxed(&lock->val, val, _Q_LOCKED_VAL);
if (old == val)