From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751375AbaHDEK4 (ORCPT ); Mon, 4 Aug 2014 00:10:56 -0400 Received: from g4t3427.houston.hp.com ([15.201.208.55]:37181 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750714AbaHDEKy (ORCPT ); Mon, 4 Aug 2014 00:10:54 -0400 Message-ID: <1407125450.4710.38.camel@j-VirtualBox> Subject: Re: [PATCH 2/7] locking/rwsem: more aggressive use of optimistic spinning From: Jason Low To: Waiman Long Cc: Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, Davidlohr Bueso , Scott J Norton , Dave Chinner Date: Sun, 03 Aug 2014 21:10:50 -0700 In-Reply-To: <1407119782-41119-3-git-send-email-Waiman.Long@hp.com> References: <1407119782-41119-1-git-send-email-Waiman.Long@hp.com> <1407119782-41119-3-git-send-email-Waiman.Long@hp.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.