Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752406Ab3FQQWK (ORCPT ); Mon, 17 Jun 2013 12:22:10 -0400 Received: from g4t0014.houston.hp.com ([15.201.24.17]:11509 "EHLO g4t0014.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751094Ab3FQQWI (ORCPT ); Mon, 17 Jun 2013 12:22:08 -0400 Message-ID: <1371486122.1778.14.camel@buesod1.americas.hpqcorp.net> Subject: Re: Performance regression from switching lock to rw-sem for anon-vma tree From: Davidlohr Bueso To: Alex Shi Cc: Tim Chen , Ingo Molnar , Rik van Riel , Peter Zijlstra , Andrea Arcangeli , Mel Gorman , Andi Kleen , Andrew Morton , Michel Lespinasse , "Wilcox, Matthew R" , Dave Hansen , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" Date: Mon, 17 Jun 2013 09:22:02 -0700 In-Reply-To: <51BD8A77.2080201@intel.com> References: <1371165333.27102.568.camel@schen9-DESK> <1371167015.1754.14.camel@buesod1.americas.hpqcorp.net> <51BD8A77.2080201@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4 (3.4.4-2.fc17) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4747 Lines: 137 On Sun, 2013-06-16 at 17:50 +0800, Alex Shi wrote: > On 06/14/2013 07:43 AM, Davidlohr Bueso wrote: > > I was hoping that the lack of spin on owner was the main difference with > > rwsems and am/was in the middle of implementing it. Could you send your > > patch so I can give it a try on my workloads? > > > > Note that there have been a few recent (3.10) changes to mutexes that > > give a nice performance boost, specially on large systems, most > > noticeably: > > > > commit 2bd2c92c (mutex: Make more scalable by doing less atomic > > operations) > > > > commit 0dc8c730 (mutex: Queue mutex spinners with MCS lock to reduce > > cacheline contention) > > > > It might be worth looking into doing something similar to commit > > 0dc8c730, in addition to the optimistic spinning. > > It is a good tunning for large machine. I just following what the commit > 0dc8c730 done, give a RFC patch here. I tried it on my NHM EP machine. seems no > clear help on aim7. but maybe it is helpful on large machine. :) After a lot of benchmarking, I finally got the ideal results for aim7, so far: this patch + optimistic spinning with preemption disabled. Just like optimistic spinning, this patch by itself makes little to no difference, yet combined is where we actually outperform 3.10-rc5. In addition, I noticed extra throughput when disabling preemption in try_optimistic_spin(). With i_mmap as a rwsem and these changes I could see performance benefits for alltests (+14.5%), custom (+17%), disk (+11%), high_systime (+5%), shared (+15%) and short (+4%), most of them after around 500 users, for fewer users, it made little to no difference. Thanks, Davidlohr > > > diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h > index bb1e2cd..240729a 100644 > --- a/include/asm-generic/rwsem.h > +++ b/include/asm-generic/rwsem.h > @@ -70,11 +70,11 @@ static inline void __down_write(struct rw_semaphore *sem) > > static inline int __down_write_trylock(struct rw_semaphore *sem) > { > - long tmp; > + if (unlikely(&sem->count != RWSEM_UNLOCKED_VALUE)) > + return 0; > > - tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, > - RWSEM_ACTIVE_WRITE_BIAS); > - return tmp == RWSEM_UNLOCKED_VALUE; > + return cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, > + RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_UNLOCKED_VALUE; > } > > /* > diff --git a/lib/rwsem.c b/lib/rwsem.c > index 19c5fa9..9e54e20 100644 > --- a/lib/rwsem.c > +++ b/lib/rwsem.c > @@ -64,7 +64,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) > struct rwsem_waiter *waiter; > struct task_struct *tsk; > struct list_head *next; > - long oldcount, woken, loop, adjustment; > + long woken, loop, adjustment; > > waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); > if (waiter->type == RWSEM_WAITING_FOR_WRITE) { > @@ -75,7 +75,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) > * will block as they will notice the queued writer. > */ > wake_up_process(waiter->task); > - goto out; > + return sem; > } > > /* Writers might steal the lock before we grant it to the next reader. > @@ -85,15 +85,28 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) > adjustment = 0; > if (wake_type != RWSEM_WAKE_READ_OWNED) { > adjustment = RWSEM_ACTIVE_READ_BIAS; > - try_reader_grant: > - oldcount = rwsem_atomic_update(adjustment, sem) - adjustment; > - if (unlikely(oldcount < RWSEM_WAITING_BIAS)) { > - /* A writer stole the lock. Undo our reader grant. */ > + while (1) { > + long oldcount; > + > + /* A writer stole the lock. */ > + if (unlikely(sem->count & RWSEM_ACTIVE_MASK)) > + return sem; > + > + if (unlikely(sem->count < RWSEM_WAITING_BIAS)) { > + cpu_relax(); > + continue; > + } > + > + oldcount = rwsem_atomic_update(adjustment, sem) > + - adjustment; > + if (likely(oldcount >= RWSEM_WAITING_BIAS)) > + break; > + > + /* A writer stole the lock. Undo our reader grant. */ > if (rwsem_atomic_update(-adjustment, sem) & > RWSEM_ACTIVE_MASK) > - goto out; > + return sem; > /* Last active locker left. Retry waking readers. */ > - goto try_reader_grant; > } > } > > @@ -136,7 +149,6 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) > sem->wait_list.next = next; > next->prev = &sem->wait_list; > > - out: > return sem; > } > > -- > Thanks > Alex > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/