From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755918Ab1IGGXW (ORCPT ); Wed, 7 Sep 2011 02:23:22 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:46715 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755866Ab1IGGWT (ORCPT ); Wed, 7 Sep 2011 02:22:19 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, 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, "Paul E. McKenney" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 36/55] rcu: Prevent early boot set_need_resched() from __rcu_pending() Date: Tue, 6 Sep 2011 11:00:30 -0700 Message-Id: <1315332049-2604-36-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20110906180015.GA2560@linux.vnet.ibm.com> References: <20110906180015.GA2560@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paul E. McKenney There isn't a whole lot of point in poking the scheduler before there are other tasks to switch to. This commit therefore adds a check for rcu_scheduler_fully_active in __rcu_pending() to suppress any pre-scheduler calls to set_need_resched(). The downside of this approach is additional runtime overhead in a reasonably hot code path. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index a07bf55..0051dbf 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1707,7 +1707,8 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) check_cpu_stall(rsp, rdp); /* Is the RCU core waiting for a quiescent state from this CPU? */ - if (rdp->qs_pending && !rdp->passed_quiesce) { + if (rcu_scheduler_fully_active && + rdp->qs_pending && !rdp->passed_quiesce) { /* * If force_quiescent_state() coming soon and this CPU -- 1.7.3.2