From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752763AbcE0Kfn (ORCPT ); Fri, 27 May 2016 06:35:43 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:37955 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752520AbcE0Kfm (ORCPT ); Fri, 27 May 2016 06:35:42 -0400 Message-Id: <201605271035.u4RAYwqn027576@mx0a-001b2d01.pphosted.com> X-IBM-Helo: d28dlp03.in.ibm.com X-IBM-MailFrom: xinhui.pan@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Fri, 27 May 2016 18:34:58 +0800 From: xinhui User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0 MIME-Version: 1.0 To: Peter Zijlstra CC: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, mingo@redhat.com, paulmck@linux.vnet.ibm.com, jeremy@goop.org, chrisw@sous-sol.org, akataria@vmware.com, rusty@rustcorp.com.au Subject: Re: [PATCH v3 5/6] pv-qspinlock: use cmpxchg_release in __pv_queued_spin_unlock References: <1464164289-6124-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <1464164289-6124-6-git-send-email-xinhui.pan@linux.vnet.ibm.com> <20160526164729.GL3206@twins.programming.kicks-ass.net> <20160526165712.GT3205@twins.programming.kicks-ass.net> In-Reply-To: <20160526165712.GT3205@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16052710-0048-0000-0000-000002810753 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16052710-0049-0000-0000-00000CCF936B X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-05-27_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=8 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1605270122 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016年05月27日 00:57, Peter Zijlstra wrote: > On Thu, May 26, 2016 at 06:47:29PM +0200, Peter Zijlstra wrote: >> On Wed, May 25, 2016 at 04:18:08PM +0800, Pan Xinhui wrote: >>> cmpxchg_release is light-wight than cmpxchg, we can gain a better >>> performace then. On some arch like ppc, barrier impact the performace >>> too much. >>> >>> Suggested-by: Boqun Feng >>> Signed-off-by: Pan Xinhui >>> --- >>> kernel/locking/qspinlock_paravirt.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h >>> index a5b1248..2bbffe4 100644 >>> --- a/kernel/locking/qspinlock_paravirt.h >>> +++ b/kernel/locking/qspinlock_paravirt.h >>> @@ -614,7 +614,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock) >>> * unhash. Otherwise it would be possible to have multiple @lock >>> * entries, which would be BAD. >>> */ >>> - locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0); >>> + locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0); >>> if (likely(locked == _Q_LOCKED_VAL)) >>> return; >> >> This patch fails to explain _why_ it can be relaxed. >> >> And seeing how this cmpxchg() can actually unlock the lock, I don't see >> how this can possibly be correct. Maybe cmpxchg_release(), but relaxed >> seems very wrong. > > Clearly I need to stop working for the day, I cannea read. You're doing > release, not relaxed. > Never mind. thanks for review :) > Still Changelog needs improvement. > Will do that. thanks xinhui