From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752156AbaHDPoX (ORCPT ); Mon, 4 Aug 2014 11:44:23 -0400 Received: from g4t3426.houston.hp.com ([15.201.208.54]:60042 "EHLO g4t3426.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751093AbaHDPoW (ORCPT ); Mon, 4 Aug 2014 11:44:22 -0400 Message-ID: <53DFAA53.4010003@hp.com> Date: Mon, 04 Aug 2014 11:44:19 -0400 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: Jason Low CC: Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, Davidlohr Bueso , Scott J Norton , Dave Chinner Subject: Re: [PATCH 2/7] locking/rwsem: more aggressive use of optimistic spinning References: <1407119782-41119-1-git-send-email-Waiman.Long@hp.com> <1407119782-41119-3-git-send-email-Waiman.Long@hp.com> <1407125450.4710.38.camel@j-VirtualBox> In-Reply-To: <1407125450.4710.38.camel@j-VirtualBox> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/04/2014 12:10 AM, Jason Low wrote: > On Sun, 2014-08-03 at 22:36 -0400, Waiman Long wrote: >> The rwsem_can_spin_on_owner() function currently allows optimistic >> spinning only if the owner field is defined and is running. That is >> too conservative as it will cause some tasks to miss the opportunity >> of doing spinning in case the owner hasn't been able to set the owner >> field in time or the lock has just become available. >> >> This patch enables more aggressive use of optimistic spinning by >> assuming that the lock is spinnable unless proved otherwise. >> >> Signed-off-by: Waiman Long >> --- >> kernel/locking/rwsem-xadd.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c >> index d058946..dce22b8 100644 >> --- a/kernel/locking/rwsem-xadd.c >> +++ b/kernel/locking/rwsem-xadd.c >> @@ -285,7 +285,7 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem) >> static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) >> { >> struct task_struct *owner; >> - bool on_cpu = false; >> + bool on_cpu = true; /* Assume spinnable unless proved not to be */ > Hi, > > So "on_cpu = true" was recently converted to "on_cpu = false" in order > to address issues such as a 5x performance regression in the xfs_repair > workload that was caused by the original rwsem optimistic spinning code. > > However, patch 4 in this patchset does address some of the problems with > spinning when there are readers. CC'ing Dave Chinner, who did the > testing with the xfs_repair workload. > This patch set enables proper reader spinning and so the problem that we see with xfs_repair workload should go away. I should have this patch after patch 4 to make it less confusing. BTW, patch 3 can significantly reduce spinlock contention in rwsem. So I believe the xfs_repair workload should run faster with this patch than both 3.15 and 3.16. -Longman