From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933828Ab0EDU0U (ORCPT ); Tue, 4 May 2010 16:26:20 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:52349 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933772Ab0EDUUS (ORCPT ); Tue, 4 May 2010 16:20:18 -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, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 02/48] rcu: substitute set_need_resched for sending resched IPIs Date: Tue, 4 May 2010 13:19:12 -0700 Message-Id: <1273004398-19760-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.0 In-Reply-To: <20100504201934.GA19234@linux.vnet.ibm.com> References: <20100504201934.GA19234@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch adds a check to __rcu_pending() that does a local set_need_resched() if the current CPU is holding up the current grace period and if force_quiescent_state() will be called soon. The goal is to reduce the probability that force_quiescent_state() will need to do smp_send_reschedule(), which sends an IPI and is therefore more expensive on most architectures. Signed-off-by: "Paul E. McKenney" --- kernel/rcutree.c | 10 ++++++++++ 1 files changed, 10 insertions(+), 0 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 3ec8160..e54c123 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1499,6 +1499,16 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) /* Is the RCU core waiting for a quiescent state from this CPU? */ if (rdp->qs_pending) { + + /* + * If force_quiescent_state() coming soon and this CPU + * needs a quiescent state, and this is either RCU-sched + * or RCU-bh, force a local reschedule. + */ + if (!rdp->preemptable && + ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1, + jiffies)) + set_need_resched(); rdp->n_rp_qs_pending++; return 1; } -- 1.7.0