Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751891AbbGaCRD (ORCPT ); Thu, 30 Jul 2015 22:17:03 -0400 Received: from g9t5009.houston.hp.com ([15.240.92.67]:34411 "EHLO g9t5009.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750789AbbGaCRB (ORCPT ); Thu, 30 Jul 2015 22:17:01 -0400 Message-ID: <55BADA98.3000304@hp.com> Date: Thu, 30 Jul 2015 22:16:56 -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: "Eric W. Biederman" CC: Andrew Morton , Nicolas Dichtel , Al Viro , Alexey Dobriyan , linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch Subject: Re: [PATCH] proc: change proc_subdir_lock to a rwlock References: <1438201199-2809-1-git-send-email-Waiman.Long@hp.com> In-Reply-To: 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 Content-Length: 1152 Lines: 28 On 07/29/2015 06:21 PM, Eric W. Biederman wrote: > Two quick questions. > > - What motivates this work? Are you seeing lots of > parallel reads on proc? The micro-benchmark that I used was artificial, but it was used to reproduce an exit hanging problem that I saw in real application. In fact, only allow one task to do a lookup seems too limiting to me. > - Why not rcu? Additions and removal of proc generic > files is very rare. Conversion to rcu for reads should > perform better and not take much more work. RCU is harder to verify its correctness, whereas rwlock is easier to use and understand. If it is really a performance critical path where every extra bit of performance counts, I will certainly think RCU may be the right choice. However, in this particular case, I don't think using RCU will give any noticeable performance gain compared with a rwlock. Cheers, Longman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/