From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755523Ab1IGGYk (ORCPT ); Wed, 7 Sep 2011 02:24:40 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:38194 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755757Ab1IGGVE (ORCPT ); Wed, 7 Sep 2011 02:21:04 -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" Subject: [PATCH tip/core/rcu 40/55] rcu: Avoid having just-onlined CPU resched itself when RCU is idle Date: Tue, 6 Sep 2011 11:00:34 -0700 Message-Id: <1315332049-2604-40-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 CPUs set rdp->qs_pending when coming online to resolve races with grace-period start. However, this means that if RCU is idle, the just-onlined CPU might needlessly send itself resched IPIs. Adjust the online-CPU initialization to avoid this, and also to correctly cause the CPU to respond to the current grace period if needed. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 11 ++++++++--- 1 files changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ade7883..c95fa89 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1911,8 +1911,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave(&rnp->lock, flags); - rdp->passed_quiesce = 0; /* We could be racing with new GP, */ - rdp->qs_pending = 1; /* so set up to respond to current GP. */ rdp->beenonline = 1; /* We have now been online. */ rdp->preemptible = preemptible; rdp->qlen_last_fqs_check = 0; @@ -1937,8 +1935,15 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rnp->qsmaskinit |= mask; mask = rnp->grpmask; if (rnp == rdp->mynode) { - rdp->gpnum = rnp->completed; /* if GP in progress... */ + /* + * If there is a grace period in progress, we will + * set up to wait for it next time we run the + * RCU core code. + */ + rdp->gpnum = rnp->completed; rdp->completed = rnp->completed; + rdp->passed_quiesce = 0; + rdp->qs_pending = 0; rdp->passed_quiesce_gpnum = rnp->gpnum - 1; trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl"); } -- 1.7.3.2