From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753680Ab3F1UKp (ORCPT ); Fri, 28 Jun 2013 16:10:45 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:42057 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753628Ab3F1UKn (ORCPT ); Fri, 28 Jun 2013 16:10:43 -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 RFC nohz_full v2 7/7] nohz_full: Force RCU's grace-period kthreads onto timekeeping CPU Date: Fri, 28 Jun 2013 13:10:22 -0700 Message-Id: <1372450222-19420-7-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1372450222-19420-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20130628200949.GA17458@linux.vnet.ibm.com> <1372450222-19420-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13062820-7282-0000-0000-000018C63825 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Because RCU's quiescent-state-forcing mechanism is used to drive the full-system-idle state machine, and because this mechanism is executed by RCU's grace-period kthreads, this commit forces these kthreads to run on the timekeeping CPU (tick_do_timer_cpu). To do otherwise would mean that the RCU grace-period kthreads would force the system into non-idle state every time they drove the state machine, which would be just a bit on the futile side. Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Steven Rostedt --- kernel/rcutree.c | 1 + kernel/rcutree.h | 1 + kernel/rcutree_plugin.h | 20 +++++++++++++++++++- 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 06cfd75..ad9a5ec 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1286,6 +1286,7 @@ static int rcu_gp_init(struct rcu_state *rsp) struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(rsp); + rcu_bind_gp_kthread(); raw_spin_lock_irq(&rnp->lock); rsp->gp_flags = 0; /* Clear all flags: New grace period. */ diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 7326a3c..1602c21 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -558,6 +558,7 @@ static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq); static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, unsigned long *maxj); static bool is_sysidle_rcu_state(struct rcu_state *rsp); +static void rcu_bind_gp_kthread(void); static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, unsigned long maxj); static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 9b60df5..4478cfd 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2543,7 +2543,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, if (!*isidle || rdp->rsp != rcu_sysidle_state || cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) return; - /* WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); */ + WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); /* * Pick up current idle and NMI-nesting counters, check. We check @@ -2577,6 +2577,20 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp) } /* + * Bind the grace-period kthread for the sysidle flavor of RCU to the + * timekeeping CPU. + */ +static void rcu_bind_gp_kthread(void) +{ + int cpu = ACCESS_ONCE(tick_do_timer_cpu); + + if (cpu < 0 || cpu >= nr_cpu_ids) + return; + if (raw_smp_processor_id() != cpu) + set_cpus_allowed_ptr(current, cpumask_of(cpu)); +} + +/* * Return a delay in jiffies based on the number of CPUs, rcu_node * leaf fanout, and jiffies tick rate. The idea is to allow larger * systems more time to transition to full-idle state in order to @@ -2744,6 +2758,10 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp) return false; } +static void rcu_bind_gp_kthread(void) +{ +} + static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, unsigned long maxj) { -- 1.8.1.5