Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753381Ab1FJHOa (ORCPT ); Fri, 10 Jun 2011 03:14:30 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:57531 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751803Ab1FJHO3 (ORCPT ); Fri, 10 Jun 2011 03:14:29 -0400 Message-ID: <4DF1C455.2080706@cn.fujitsu.com> Date: Fri, 10 Jun 2011 15:14:29 +0800 From: Lai Jiangshan User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc14 Thunderbird/3.1.4 MIME-Version: 1.0 To: "Paul E. McKenney" CC: linux-kernel@vger.kernel.org, mingo@elte.hu, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org Subject: Re: [PATCH tip/core/rcu 03/28] rcu: Streamline code produced by __rcu_read_unlock() References: <20110608192943.GA13211@linux.vnet.ibm.com> <1307561407-13809-3-git-send-email-paulmck@linux.vnet.ibm.com> In-Reply-To: <1307561407-13809-3-git-send-email-paulmck@linux.vnet.ibm.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-06-10 15:14:09, Serialize by Router on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-06-10 15:14:13, Serialize complete at 2011-06-10 15:14:13 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2425 Lines: 58 On 06/09/2011 03:29 AM, Paul E. McKenney wrote: > Given some common flag combinations, particularly -Os, gcc will inline > rcu_read_unlock_special() despite its being in an unlikely() clause. > Use noline to prohibit this misoptimization. > > In addition, move the second barrier() in __rcu_read_unlock() so that > it is not on the common-case code path. This will allow the compiler to > generate better code for the common-case path through __rcu_read_unlock(). > > Finally, fix up whitespace in kernel/lockdep.c to keep checkpatch happy. > > Suggested-by: Linus Torvalds > Signed-off-by: Paul E. McKenney > --- > kernel/rcutree_plugin.h | 12 ++++++------ > 1 files changed, 6 insertions(+), 6 deletions(-) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index ea2e2fb..40a6db7 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -284,7 +284,7 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t, > * notify RCU core processing or task having blocked during the RCU > * read-side critical section. > */ > -static void rcu_read_unlock_special(struct task_struct *t) > +static noinline void rcu_read_unlock_special(struct task_struct *t) > { > int empty; > int empty_exp; > @@ -387,11 +387,11 @@ void __rcu_read_unlock(void) > struct task_struct *t = current; > > barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ > - --t->rcu_read_lock_nesting; > - barrier(); /* decrement before load of ->rcu_read_unlock_special */ > - if (t->rcu_read_lock_nesting == 0 && > - unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) > - rcu_read_unlock_special(t); > + if (--t->rcu_read_lock_nesting == 0) { > + barrier(); /* decr before ->rcu_read_unlock_special load */ Since ACCESS_ONCE() is used for loading ->rcu_read_unlock_special, is the previous barrier() still needed? > + if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) > + rcu_read_unlock_special(t); > + } > #ifdef CONFIG_PROVE_LOCKING > WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); > #endif /* #ifdef CONFIG_PROVE_LOCKING */ -- 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/