From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752338Ab2LTSkV (ORCPT ); Thu, 20 Dec 2012 13:40:21 -0500 Received: from mail-wi0-f170.google.com ([209.85.212.170]:49042 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752267Ab2LTSj7 (ORCPT ); Thu, 20 Dec 2012 13:39:59 -0500 From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Alessio Igor Bogani , Andrew Morton , Avi Kivity , Chris Metcalf , Christoph Lameter , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Ingo Molnar , "Paul E. McKenney" , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner Subject: [PATCH 22/24] nohz: Don't turn off the tick if rcu needs it Date: Thu, 20 Dec 2012 19:33:09 +0100 Message-Id: <1356028391-14427-23-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1356028391-14427-1-git-send-email-fweisbec@gmail.com> References: <1356028391-14427-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If RCU is waiting for the current CPU to complete a grace period, don't turn off the tick. Unlike dynctik-idle, we are not necessarily going to enter into rcu extended quiescent state, so we may need to keep the tick to note current CPU's quiescent states. [added build fix from Zen Lin] CHECKME: OTOH we don't want to handle a locally started grace period, this should be offloaded for rcu_nocb CPUs. What we want is to be kicked if we stay dynticks in the kernel for too long (ie: to report a quiescent state). rcu_pending() is perhaps an overkill just for that. Signed-off-by: Frederic Weisbecker Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Avi Kivity Cc: Chris Metcalf Cc: Christoph Lameter Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Paul E. McKenney Cc: Paul Gortmaker Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Signed-off-by: Steven Rostedt --- include/linux/rcupdate.h | 1 + kernel/rcutree.c | 3 +-- kernel/time/tick-sched.c | 3 +++ 3 files changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 829312e..2ebadac 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -211,6 +211,7 @@ static inline int rcu_preempt_depth(void) extern void rcu_sched_qs(int cpu); extern void rcu_bh_qs(int cpu); extern void rcu_check_callbacks(int cpu, int user); +extern int rcu_pending(int cpu); struct notifier_block; extern void rcu_idle_enter(void); extern void rcu_idle_exit(void); diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e9e0ffa..6ba3e02 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -232,7 +232,6 @@ module_param(jiffies_till_next_fqs, ulong, 0644); static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); static void force_quiescent_state(struct rcu_state *rsp); -static int rcu_pending(int cpu); /* * Return the number of RCU-sched batches processed thus far for debug & stats. @@ -2521,7 +2520,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) * by the current CPU, returning 1 if so. This function is part of the * RCU implementation; it is -not- an exported member of the RCU API. */ -static int rcu_pending(int cpu) +int rcu_pending(int cpu) { struct rcu_state *rsp; diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 2808e02..0c9281a 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -594,6 +594,9 @@ static bool can_stop_full_tick(int cpu) if (!rcu_is_nocb_cpu(cpu)) return false; + if (rcu_pending(cpu)) + return false; + return true; } #endif -- 1.7.5.4