From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754045AbeDWDCq (ORCPT ); Sun, 22 Apr 2018 23:02:46 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:34020 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753905AbeDWDCi (ORCPT ); Sun, 22 Apr 2018 23:02:38 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel.opensrc@gmail.com, torvalds@linux-foundation.org, npiggin@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 04/21] rcu: Make rcu_gp_kthread() check for early-boot activity Date: Sun, 22 Apr 2018 20:03:27 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20180423030258.GA23370@linux.vnet.ibm.com> References: <20180423030258.GA23370@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18042303-2213-0000-0000-0000029783A1 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008903; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000257; SDB=6.01021898; UDB=6.00521542; IPR=6.00801133; MB=3.00020719; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-23 03:02:35 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18042303-2214-0000-0000-000059DC4067 Message-Id: <1524452624-27589-4-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-23_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804230032 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The rcu_gp_kthread() function immediately sleeps waiting to be notified of the need for a new grace period, which currently works because there are a number of code sequences that will provide the needed wakeup later. However, some of these code sequences need to acquire the root rcu_node structure's ->lock, and contention on that lock has started manifesting. This commit therefore makes rcu_gp_kthread() check for early-boot activity when it starts up, omitting the initial sleep in that case. Reported-by: Nicholas Piggin Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 79fb99951a0c..497f139056c7 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2192,6 +2192,12 @@ static int __noreturn rcu_gp_kthread(void *arg) struct rcu_state *rsp = arg; struct rcu_node *rnp = rcu_get_root(rsp); + /* Check for early-boot work. */ + raw_spin_lock_irq_rcu_node(rnp); + if (need_any_future_gp(rnp)) + WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT); + raw_spin_unlock_irq_rcu_node(rnp); + rcu_bind_gp_kthread(); for (;;) { -- 2.5.2