[tip: core/rcu] rcu-tasks: Add a grace-period start time for throttling and debug

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     88092d0c99d7584d50cc8caadb8fa9ff8a1d4ea0
Gitweb:        https://git.kernel.org/tip/88092d0c99d7584d50cc8caadb8fa9ff8a1d4ea0
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Tue, 17 Mar 2020 08:57:02 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 27 Apr 2020 11:03:52 -07:00

rcu-tasks: Add a grace-period start time for throttling and debug

This commit adds a place to record the grace-period start in jiffies.
This will be used by later commits for debugging purposes and to throttle
IPIs early in the grace period.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tasks.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 6f8a404..71462cf 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -46,6 +46,7 @@ struct rcu_tasks {
 	raw_spinlock_t cbs_lock;
 	int gp_state;
 	unsigned long gp_jiffies;
+	unsigned long gp_start;
 	struct task_struct *kthread_ptr;
 	rcu_tasks_gp_func_t gp_func;
 	pregp_func_t pregp_func;
@@ -200,6 +201,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
 
 		// Wait for one grace period.
 		set_tasks_gp_state(rtp, RTGS_WAIT_GP);
+		rtp->gp_start = jiffies;
 		rtp->gp_func(rtp);
 
 		/* Invoke the callbacks. */