From patchwork Tue Sep 6 17:59:56 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 3920 Return-Path: X-Original-To: patchwork@peony.canonical.com Delivered-To: patchwork@peony.canonical.com Received: from fiordland.canonical.com (fiordland.canonical.com [91.189.94.145]) by peony.canonical.com (Postfix) with ESMTP id 51D8523FC5 for ; Wed, 7 Sep 2011 06:20:55 +0000 (UTC) Received: from mail-fx0-f52.google.com (mail-fx0-f52.google.com [209.85.161.52]) by fiordland.canonical.com (Postfix) with ESMTP id 46272A186A3 for ; Wed, 7 Sep 2011 06:20:55 +0000 (UTC) Received: by mail-fx0-f52.google.com with SMTP id 18so398726fxd.11 for ; Tue, 06 Sep 2011 23:20:55 -0700 (PDT) Received: by 10.223.24.21 with SMTP id t21mr2892720fab.24.1315376454982; Tue, 06 Sep 2011 23:20:54 -0700 (PDT) X-Forwarded-To: linaro-patchwork@canonical.com X-Forwarded-For: patch@linaro.org linaro-patchwork@canonical.com Delivered-To: patches@linaro.org Received: by 10.152.11.8 with SMTP id m8cs127783lab; Tue, 6 Sep 2011 23:20:54 -0700 (PDT) Received: by 10.236.181.101 with SMTP id k65mr29550879yhm.65.1315376452287; Tue, 06 Sep 2011 23:20:52 -0700 (PDT) Received: from e7.ny.us.ibm.com (e7.ny.us.ibm.com [32.97.182.137]) by mx.google.com with ESMTPS id a14si2510820ybk.53.2011.09.06.23.20.50 (version=TLSv1/SSLv3 cipher=OTHER); Tue, 06 Sep 2011 23:20:51 -0700 (PDT) Received-SPF: pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.182.137 as permitted sender) client-ip=32.97.182.137; Authentication-Results: mx.google.com; spf=pass (google.com: domain of paulmck@linux.vnet.ibm.com designates 32.97.182.137 as permitted sender) smtp.mail=paulmck@linux.vnet.ibm.com Received: from d01relay06.pok.ibm.com (d01relay06.pok.ibm.com [9.56.227.116]) by e7.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p8750XQF028461; Wed, 7 Sep 2011 01:00:33 -0400 Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay06.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p876KnZu1667182; Wed, 7 Sep 2011 02:20:49 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p876KipK005673; Wed, 7 Sep 2011 02:20:48 -0400 Received: from paulmck-ThinkPad-W500 (dyn9050016039.mts.ibm.com [9.50.16.39] (may be forged)) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id p876KZHL004574; Wed, 7 Sep 2011 02:20:42 -0400 Received: by paulmck-ThinkPad-W500 (Postfix, from userid 1000) id 411E513F7C6; Tue, 6 Sep 2011 11:00:51 -0700 (PDT) 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, Shaohua Li , "Paul E. McKenney" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 02/55] rcu: Avoid unnecessary self-wakeup of per-CPU kthreads Date: Tue, 6 Sep 2011 10:59:56 -0700 Message-Id: <1315332049-2604-2-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> From: Shaohua Li There are a number of cases where the RCU can find additional work for the per-CPU kthread within the context of that per-CPU kthread. In such cases, the per-CPU kthread is already running, so attempting to wake itself up does nothing except waste CPU cycles. This commit therefore checks to see if it is in the per-CPU kthread context, omitting the wakeup in this case. Signed-off-by: Shaohua Li Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 8 +++----- 1 files changed, 3 insertions(+), 5 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7b850cd..9703298 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1291,11 +1291,9 @@ static void invoke_rcu_callbacks_kthread(void) local_irq_save(flags); __this_cpu_write(rcu_cpu_has_work, 1); - if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) { - local_irq_restore(flags); - return; - } - wake_up_process(__this_cpu_read(rcu_cpu_kthread_task)); + if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && + current != __this_cpu_read(rcu_cpu_kthread_task)) + wake_up_process(__this_cpu_read(rcu_cpu_kthread_task)); local_irq_restore(flags); }