From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755532AbYKJSpb (ORCPT ); Mon, 10 Nov 2008 13:45:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753859AbYKJSpX (ORCPT ); Mon, 10 Nov 2008 13:45:23 -0500 Received: from e2.ny.us.ibm.com ([32.97.182.142]:37035 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752836AbYKJSpW (ORCPT ); Mon, 10 Nov 2008 13:45:22 -0500 Date: Mon, 10 Nov 2008 10:45:20 -0800 From: "Paul E. McKenney" To: Lai Jiangshan Cc: Ingo Molnar , Peter Zijlstra , Andrew Morton , Linux Kernel Mailing List Subject: Re: [PATCH] rcupdate: move synchronize_sched() back to rcupdate.c V2 Message-ID: <20081110184520.GC6685@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <49129310.5000903@cn.fujitsu.com> <20081109005159.GM6917@linux.vnet.ibm.com> <4917A8E7.8060801@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4917A8E7.8060801@cn.fujitsu.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 10, 2008 at 11:22:15AM +0800, Lai Jiangshan wrote: > Paul E. McKenney wrote: > > On Thu, Nov 06, 2008 at 02:47:44PM +0800, Lai Jiangshan wrote: > >> this fix remove ugly macro, and increase readability for rcupdate codes > >> > >> changed from v1: > >> use HAVE_SPECIAL_RCU_BH/SCHED instead of define duplicate version of > >> synchronize_sched(). > > > > Hello, Jiangshan! > > > > I very much like getting rid of the ugly macro. I of course like the > > kernel-doc fixes. ;-) > > > > I am not yet convinced of the HAVE_SPECIAL_RCU_BH and > > HAVE_SPECIAL_RCU_SCHED pieces. It is not clear to me that this approach > > is simpler than the current approach of simply providing the appropriate > > definitions for the symbols in the implementation-specific rcuxxx.h > > file. > > > > Am I missing something? > > > > Thanx, Paul > > > > I think: > > RCU_BH is not required, we can used RCU instead. so HAVE_SPECIAL_RCU_BH > will help for implementation which has not RCU_BH. > > HAVE_SPECIAL_RCU_SCHED is a little different, RCU and RCU_SCHED are both > required for the kernel. But I think, in an implementation, > if rcu_read_lock_sched() implies rcu_read_lock(), we may not need implement > RCU_SCHED too(sometimes we may implement RCU_SCHED for performance). > so HAVE_SPECIAL_RCU_SCHED will help. If I understand correctly, this is the "old way": ------------------------------------------------------------------------ rcupdate.h: #define rcu_read_lock_bh() __rcu_read_lock_bh() #define rcu_read_unlock_bh() __rcu_read_unlock_bh() rcupreempt.h: #define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); } #define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); } ------------------------------------------------------------------------ And then this is the "new way": ------------------------------------------------------------------------ rcupdate.h: #ifdef HAVE_SPECIAL_RCU_BH #define rcu_read_lock_bh() __rcu_read_lock_bh() #define rcu_read_unlock_bh() __rcu_read_unlock_bh() #else #define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); } #define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); } #endif /* HAVE_SPECIAL_RCU_BH */ rcupreempt.h: #define HAVE_SPECIAL_RCU_BH ------------------------------------------------------------------------ If we had ten different RCU implementations, then the "new way" would save a little bit of code. But the "old way" is a bit easier to figure out. So I am in favor of getting rid of the ugly macro, and also in favor of fixing the kerneldoc, but opposed to the HAVE_SPECIAL_RCU_BH and HAVE_SPECIAL_RCU_SCHED changes. Or am I missing something? Thanx, Paul