Commit b14fb4fb authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu-tasks: Convert grace-period counter to grace-period sequence number 



This commit moves the rcu_tasks structure's ->n_gps grace-period-counter
field to a ->task_gp_seq grce-period sequence number in order to enable
use of the rcu_segcblist structure for the callback lists.  This in turn
permits CPUs to lag behind the RCU Tasks grace-period sequence number
without suffering long-term slowdowns in callback invocation.

Reported-by: default avatarMartin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 7a30871b

kernel/rcu/tasks.h

+5 −4
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ struct rcu_tasks_percpu { 
 * @init_fract: Initial backoff sleep interval.

 * @gp_jiffies: Time of last @gp_state transition.

 * @gp_start: Most recent grace-period start in jiffies.

 * @n_gps: Number of grace periods completed since boot.

 * @tasks_gp_seq: Number of grace periods completed since boot.

 * @n_ipis: Number of IPIs sent to encourage grace periods to end.

 * @n_ipis_fails: Number of IPI-send failures.

 * @pregp_func: This flavor's pre-grace-period function (optional).
@@ -64,7 +64,7 @@ struct rcu_tasks { 
	int init_fract;

	unsigned long gp_jiffies;

	unsigned long gp_start;

	unsigned long n_gps;

	unsigned long tasks_gp_seq;

	unsigned long n_ipis;

	unsigned long n_ipis_fails;

	struct task_struct *kthread_ptr;
@@ -273,8 +273,9 @@ 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;

		rcu_seq_start(&rtp->tasks_gp_seq);

		rtp->gp_func(rtp);

		rtp->n_gps++;

		rcu_seq_end(&rtp->tasks_gp_seq);



		/* Invoke the callbacks. */

		set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
@@ -335,7 +336,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) 
		rtp->kname,

		tasks_gp_state_getname(rtp), data_race(rtp->gp_state),

		jiffies - data_race(rtp->gp_jiffies),

		data_race(rtp->n_gps),

		data_race(rcu_seq_current(&rtp->tasks_gp_seq)),

		data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),

		".k"[!!data_race(rtp->kthread_ptr)],

		".C"[!!data_race(rtpcp->cbs_head)],