lkml.org 
[lkml]   [2018]   [Apr]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 03/10] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue
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

\
 
 \ /
  Last update: 2018-04-06 12:54    [W:0.077 / U:0.400 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site