Messages in this thread Patch in this message |  | | Date | Thu, 5 Apr 2018 19:19:12 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 03/10] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue |
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On Thu, Apr 05, 2018 at 05:59:00PM +0100, Will Deacon wrote: > + > + /* In the PV case we might already have _Q_LOCKED_VAL set */ > + if ((val & _Q_TAIL_MASK) == tail) { > /* > * The smp_cond_load_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 */ > }
--- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -464,8 +464,7 @@ void queued_spin_lock_slowpath(struct qs * The smp_cond_load_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) + if (atomic_try_cmpxchg_release(&lock->val, &val, _Q_LOCKED_VAL)) goto release; /* No contention */ }
Does that also work for you? It would generate slightly better code for x86 (not that it would matter much on this path).
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