From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756067Ab0C2Crx (ORCPT ); Sun, 28 Mar 2010 22:47:53 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:64957 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1755845Ab0C2Crv (ORCPT ); Sun, 28 Mar 2010 22:47:51 -0400 Message-ID: <4BB014DF.9030905@cn.fujitsu.com> Date: Mon, 29 Mar 2010 10:47:59 +0800 From: Lai Jiangshan User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: "Paul E. McKenney" , Ingo Molnar , LKML Subject: [PATCH] rcu: don't call rcu_preempt_note_context_switch() in rcu_check_callbacks() Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Even though in user mode or idle mode, rcu_check_callbacks() is not context switch, so we don't call rcu_preempt_note_context_switch() in rcu_check_callbacks(). Though there is no harm that calls rcu_preempt_note_context_switch() in rcu_check_callbacks(), but it is waste. rcu_check_callbacks() rcu_sched_qs() rcu_preempt_note_context_switch() Now, ->rcu_read_lock_nesting == 0, so we just calls rcu_preempt_qs(), but, rcu_preempt_check_callbacks() will call it again and set the ->rcu_read_unlock_special correct again. So let rcu_preempt_check_callbacks() handle things for us. Signed-off-by: Lai Jiangshan --- diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 3ec8160..c7847ba 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -95,7 +95,7 @@ static int rcu_gp_in_progress(struct rcu_state *rsp) * how many quiescent states passed, just if there was at least * one since the start of the grace period, this just sets a flag. */ -void rcu_sched_qs(int cpu) +static void __rcu_sched_qs(int cpu) { struct rcu_data *rdp; @@ -103,6 +103,11 @@ void rcu_sched_qs(int cpu) rdp->passed_quiesc_completed = rdp->gpnum - 1; barrier(); rdp->passed_quiesc = 1; +} + +void rcu_sched_qs(int cpu) +{ + __rcu_sched_qs(cpu); rcu_preempt_note_context_switch(cpu); } @@ -1138,12 +1143,12 @@ void rcu_check_callbacks(int cpu, int user) * a quiescent state, so note it. * * No memory barrier is required here because both - * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local + * __rcu_sched_qs() and rcu_bh_qs() reference only CPU-local * variables that other CPUs neither access nor modify, * at least not while the corresponding CPU is online. */ - rcu_sched_qs(cpu); + __rcu_sched_qs(cpu); rcu_bh_qs(cpu); } else if (!in_softirq()) {