From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754982Ab3HRBjh (ORCPT ); Sat, 17 Aug 2013 21:39:37 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:45484 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753189Ab3HRBiI (ORCPT ); Sat, 17 Aug 2013 21:38:08 -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, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 07/11] rcu: Avoid redundant grace-period kthread wakeups Date: Sat, 17 Aug 2013 18:37:52 -0700 Message-Id: <1376789876-27594-7-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1376789876-27594-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20130818013735.GA27234@linux.vnet.ibm.com> <1376789876-27594-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13081801-7182-0000-0000-0000081FEFBC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" When setting up an in-the-future "advanced" grace period, the code needs to wake up the relevant grace-period kthread, which it currently does unconditionally. However, this results in needless wakeups in the case where the advanced grace period is being set up by the grace-period kthread itself, which is a non-uncommon situation. This commit therefore checks to see if the running thread is the grace-period kthread, and avoids doing the irq_work_queue()-mediated wakeup in that case. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 9184056..c6a064a 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1576,10 +1576,12 @@ rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, /* * We can't do wakeups while holding the rnp->lock, as that - * could cause possible deadlocks with the rq->lock. Deter - * the wakeup to interrupt context. + * could cause possible deadlocks with the rq->lock. Defer + * the wakeup to interrupt context. And don't bother waking + * up the running kthread. */ - irq_work_queue(&rsp->wakeup_work); + if (current != rsp->gp_kthread) + irq_work_queue(&rsp->wakeup_work); } /* -- 1.8.1.5