lkml.org 
[lkml]   [2016]   [May]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 5/6] pv-qspinlock: use cmpxchg_release in __pv_queued_spin_unlock
On Thu, May 26, 2016 at 06:47:29PM +0200, Peter Zijlstra wrote:
> On Wed, May 25, 2016 at 04:18:08PM +0800, Pan Xinhui wrote:
> > cmpxchg_release is light-wight than cmpxchg, we can gain a better
> > performace then. On some arch like ppc, barrier impact the performace
> > too much.
> >
> > Suggested-by: Boqun Feng <boqun.feng@gmail.com>
> > Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
> > ---
> > kernel/locking/qspinlock_paravirt.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> > index a5b1248..2bbffe4 100644
> > --- a/kernel/locking/qspinlock_paravirt.h
> > +++ b/kernel/locking/qspinlock_paravirt.h
> > @@ -614,7 +614,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
> > * unhash. Otherwise it would be possible to have multiple @lock
> > * entries, which would be BAD.
> > */
> > - locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
> > + locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
> > if (likely(locked == _Q_LOCKED_VAL))
> > return;
>
> This patch fails to explain _why_ it can be relaxed.
>
> And seeing how this cmpxchg() can actually unlock the lock, I don't see
> how this can possibly be correct. Maybe cmpxchg_release(), but relaxed
> seems very wrong.

Clearly I need to stop working for the day, I cannea read. You're doing
release, not relaxed.

Still Changelog needs improvement.

\
 
 \ /
  Last update: 2016-05-26 19:21    [W:0.066 / U:0.292 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site