From b0afa0f056676ffe0a7213818f09d2460adbcc16 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 17 Mar 2020 11:39:26 -0700 Subject: rcu-tasks: Provide boot parameter to delay IPIs until late in grace period This commit provides a rcupdate.rcu_task_ipi_delay kernel boot parameter that specifies how old the RCU tasks trace grace period must be before the grace-period kthread starts sending IPIs. This delay allows more tasks to pass through rcu_tasks_qs() quiescent states, thus reducing (or even eliminating) the number of IPIs that must be sent. On a short rcutorture test setting this kernel boot parameter to HZ/2 resulted in zero IPIs for all 877 RCU-tasks trace grace periods that elapsed during that test. Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 71462cf3d4bd..eeac4a122234 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -74,6 +74,11 @@ static struct rcu_tasks rt_name = \ /* Track exiting tasks in order to allow them to be waited for. */ DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); +/* Avoid IPIing CPUs early in the grace period. */ +#define RCU_TASK_IPI_DELAY (HZ / 2) +static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY; +module_param(rcu_task_ipi_delay, int, 0644); + /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10) static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT; @@ -713,6 +718,10 @@ DECLARE_WAIT_QUEUE_HEAD(trc_wait); // List of holdout tasks. // Record outstanding IPIs to each CPU. No point in sending two... static DEFINE_PER_CPU(bool, trc_ipi_to_cpu); +void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); +DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace, + "RCU Tasks Trace"); + /* If we are the last reader, wake up the grace-period kthread. */ void rcu_read_unlock_trace_special(struct task_struct *t) { @@ -998,10 +1007,6 @@ void exit_tasks_rcu_finish_trace(struct task_struct *t) rcu_read_unlock_trace_special(t); } -void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); -DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace, - "RCU Tasks Trace"); - /** * call_rcu_tasks_trace() - Queue a callback trace task-based grace period * @rhp: structure to be used for queueing the RCU updates. -- cgit v1.2.3-59-g8ed1b