From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753183AbcHJUZD (ORCPT ); Wed, 10 Aug 2016 16:25:03 -0400 Received: from mx0b-0016f401.pphosted.com ([67.231.156.173]:38802 "EHLO mx0b-0016f401.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932820AbcHJSUr (ORCPT ); Wed, 10 Aug 2016 14:20:47 -0400 Date: Wed, 10 Aug 2016 19:06:44 +0800 From: Jisheng Zhang To: Arnd Bergmann , , CC: , Subject: Re: [PATCH] ARM: cpuidle: declare cpuidle_ops __read_mostly Message-ID: <20160810190644.68966492@xhacker> In-Reply-To: <8191851.HcPOqTYLq8@wuerfel> References: <1470818997-808-1-git-send-email-jszhang@marvell.com> <2118361.tr3K3hSZxF@wuerfel> <20160810171926.44557e35@xhacker> <8191851.HcPOqTYLq8@wuerfel> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-10_09:,, signatures=0 X-Proofpoint-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1608100119 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dear Arnd, On Wed, 10 Aug 2016 12:47:21 +0200 Arnd Bergmann wrote: > On Wednesday, August 10, 2016 5:19:26 PM CEST Jisheng Zhang wrote: > > Dear Arnd, > > > > On Wed, 10 Aug 2016 10:57:57 +0200 Arnd Bergmann wrote: > > > > > On Wednesday, August 10, 2016 4:49:57 PM CEST Jisheng Zhang wrote: > > > > diff --git a/arch/arm/kernel/cpuidle.c b/arch/arm/kernel/cpuidle.c > > > > index 7dccc96..762e0929 100644 > > > > --- a/arch/arm/kernel/cpuidle.c > > > > +++ b/arch/arm/kernel/cpuidle.c > > > > @@ -19,7 +19,7 @@ extern struct of_cpuidle_method __cpuidle_method_of_table[]; > > > > static const struct of_cpuidle_method __cpuidle_method_of_table_sentinel > > > > __used __section(__cpuidle_method_of_table_end); > > > > > > > > -static struct cpuidle_ops cpuidle_ops[NR_CPUS]; > > > > +static struct cpuidle_ops cpuidle_ops[NR_CPUS] __read_mostly; > > > > > > Should this perhaps be percpu data instead? > > > > > > > Per my understanding, percpu is used for those vars with normal read/write > > frequency, while the cpuidle_ops is read mostly, so IMHO, __read_mostly > > is suitable, what do you think? > > You are right, __read_mostly is better than the normal .data section here, > but percpu is also better than .data because it saves a little memory > on machines that have few present CPUs than CONFIG_NR_CPUS. > > So both have their advantages, we just need to pick a preference. > > Actually __ro_after_init would be even better than __read_mostly here > I think, as this is only updated in an __init function. I guess > using that would have the added security advantage of preventing > an attacker from writing to the function pointers when they > find a way to overflow an access in the percpu data section. > Got it, thanks for the detailed explanations. And I think the answer to questions: http://lists.infradead.org/pipermail/linux-arm-kernel/2016-August/448057.html and http://lists.infradead.org/pipermail/linux-arm-kernel/2016-August/448059.html are both "yes" Thanks, Jisheng