Messages in this thread | | | Date | Fri, 27 May 2016 18:34:58 +0800 | From | xinhui <> | Subject | Re: [PATCH v3 5/6] pv-qspinlock: use cmpxchg_release in __pv_queued_spin_unlock |
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On 2016年05月27日 00:57, Peter Zijlstra wrote: > 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. > Never mind. thanks for review :)
> Still Changelog needs improvement. > Will do that.
thanks xinhui
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