From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753916AbcAVOAG (ORCPT ); Fri, 22 Jan 2016 09:00:06 -0500 Received: from g2t4619.austin.hp.com ([15.73.212.82]:38113 "EHLO g2t4619.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753840AbcAVOAD (ORCPT ); Fri, 22 Jan 2016 09:00:03 -0500 Message-ID: <56A235DC.2060900@hpe.com> Date: Fri, 22 Jan 2016 08:59:56 -0500 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Peter Zijlstra CC: Jason Low , Ding Tianhong , Ingo Molnar , "linux-kernel@vger.kernel.org" , Davidlohr Bueso , Linus Torvalds , "Paul E. McKenney" , Thomas Gleixner , Will Deacon , Tim Chen , Waiman Long Subject: Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list is not NULL. References: <56A0A4ED.3070308@huawei.com> <56A1638A.7050202@hpe.com> <20160122085422.GO6357@twins.programming.kicks-ass.net> <1453458019.9727.8.camel@j-VirtualBox> <20160122105312.GQ6357@twins.programming.kicks-ass.net> <20160122105652.GE6375@twins.programming.kicks-ass.net> <20160122110653.GF6375@twins.programming.kicks-ass.net> In-Reply-To: <20160122110653.GF6375@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/22/2016 06:06 AM, Peter Zijlstra wrote: > On Fri, Jan 22, 2016 at 11:56:52AM +0100, Peter Zijlstra wrote: >> On Fri, Jan 22, 2016 at 11:53:12AM +0100, Peter Zijlstra wrote: >> >>> There might be other details, but this is the one that stood out. >> I think this also does the wrong thing for use_ww_ctx. > Something like so? I think that should work. My only minor concern is that putting the waiter spinner at the end of the OSQ will take it longer to get the lock, but that shouldn't be a big issue. > --- > kernel/locking/mutex.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index 0551c219c40e..070a0ac34aa7 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -512,6 +512,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, > struct task_struct *task = current; > struct mutex_waiter waiter; > unsigned long flags; > + bool acquired; > int ret; > > preempt_disable(); > @@ -543,6 +544,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, > lock_contended(&lock->dep_map, ip); > > for (;;) { > + acquired = false; > /* > * Lets try to take the lock again - this is needed even if > * we get here for the first time (shortly after failing to > @@ -577,7 +579,16 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, > /* didn't get the lock, go to sleep: */ > spin_unlock_mutex(&lock->wait_lock, flags); > schedule_preempt_disabled(); > + > + if (mutex_is_locked(lock)) > + acquired = mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx); > + > spin_lock_mutex(&lock->wait_lock, flags); > + > + if (acquired) { > + atomic_set(&lock->count, -1); > + break; > + } > } > __set_task_state(task, TASK_RUNNING); > > @@ -587,6 +598,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, > atomic_set(&lock->count, 0); > debug_mutex_free_waiter(&waiter); > > + if (acquired) > + goto unlock; > + > skip_wait: > /* got the lock - cleanup and rejoice! */ > lock_acquired(&lock->dep_map, ip); > @@ -597,6 +611,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, > ww_mutex_set_context_slowpath(ww, ww_ctx); > } > > +unlock: > spin_unlock_mutex(&lock->wait_lock, flags); > preempt_enable(); > return 0; Cheers, Longman