From eb75767be0e514f97bf1b5cec763696cfc7f7e2a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 21 Jun 2013 17:10:40 -0700 Subject: nohz_full: Force RCU's grace-period kthreads onto timekeeping CPU 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 Cc: Lai Jiangshan Reviewed-by: Josh Triplett --- kernel/rcutree_plugin.h | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) (limited to 'kernel/rcutree_plugin.h') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 45ebba7..130c97b 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2531,7 +2531,8 @@ 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); */ + if (rcu_gp_in_progress(rdp->rsp)) + WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); /* Pick up current idle and NMI-nesting counter and check. */ cur = atomic_read(&rdtp->dynticks_idle); @@ -2557,6 +2558,20 @@ 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 @@ -2766,6 +2781,10 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp) return false; } +static void rcu_bind_gp_kthread(void) +{ +} + static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, unsigned long maxj) { -- cgit v1.1