Messages in this thread |  | | Date | Fri, 6 Apr 2018 11:54:17 +0100 | From | Will Deacon <> | 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 07:19:12PM +0200, Peter Zijlstra wrote: > 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).
Assuming you meant to use atomic_try_cmpxchg_relaxed, then that works for me too.
Will
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