From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932282AbaA1UUu (ORCPT ); Tue, 28 Jan 2014 15:20:50 -0500 Received: from e31.co.us.ibm.com ([32.97.110.149]:56541 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932117AbaA1UUq (ORCPT ); Tue, 28 Jan 2014 15:20:46 -0500 Date: Tue, 28 Jan 2014 12:20:42 -0800 From: "Paul E. McKenney" To: Jason Low Cc: mingo@redhat.com, peterz@infradead.org, Waiman.Long@hp.com, torvalds@linux-foundation.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, riel@redhat.com, akpm@linux-foundation.org, davidlohr@hp.com, hpa@zytor.com, andi@firstfloor.org, aswin@hp.com, scott.norton@hp.com, chegu_vinod@hp.com Subject: Re: [PATCH v2 1/5] mutex: In mutex_can_spin_on_owner(), return false if task need_resched() Message-ID: <20140128202042.GN9012@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1390936396-3962-1-git-send-email-jason.low2@hp.com> <1390936396-3962-2-git-send-email-jason.low2@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1390936396-3962-2-git-send-email-jason.low2@hp.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14012820-8236-0000-0000-0000067D5989 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 28, 2014 at 11:13:12AM -0800, Jason Low wrote: > The mutex_can_spin_on_owner() function should also return false if the > task needs to be rescheduled to avoid entering the MCS queue when it > needs to reschedule. > > Signed-off-by: Jason Low Reviewed-by: Paul E. McKenney But I cannot help asking how this affects performance. (My guess is "not much", but always good to know.) > --- > kernel/locking/mutex.c | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index 4dd6e4c..85c6be1 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -212,6 +212,9 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock) > struct task_struct *owner; > int retval = 1; > > + if (need_resched()) > + return 0; > + > rcu_read_lock(); > owner = ACCESS_ONCE(lock->owner); > if (owner) > -- > 1.7.1 >