The following commit has been merged into the core/rcu branch of tip: Commit-ID: b0afa0f056676ffe0a7213818f09d2460adbcc16 Gitweb: https://git.kernel.org/tip/b0afa0f056676ffe0a7213818f09d2460adbcc16 Author: Paul E. McKenney <paulmck@xxxxxxxxxx> AuthorDate: Tue, 17 Mar 2020 11:39:26 -07:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Mon, 27 Apr 2020 11:03:52 -07:00 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 <paulmck@xxxxxxxxxx> --- Documentation/admin-guide/kernel-parameters.txt | 7 +++++++ kernel/rcu/tasks.h | 13 +++++++++---- 2 files changed, 16 insertions(+), 4 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f2a93c8..aaa8678 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4286,6 +4286,13 @@ only normal grace-period primitives. No effect on CONFIG_TINY_RCU kernels. + rcupdate.rcu_task_ipi_delay= [KNL] + Set time in jiffies during which RCU tasks will + avoid sending IPIs, starting with the beginning + of a given grace period. Setting a large + number avoids disturbing real-time workloads, + but lengthens grace periods. + rcupdate.rcu_task_stall_timeout= [KNL] Set timeout in jiffies for RCU task stall warning messages. Disable with a value less than or equal diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 71462cf..eeac4a1 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.
![]() |