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Commit b40d293e authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Paul E. McKenney
Browse files

rcu: Omit self-awaken when setting up expedited grace period 



When setting up an expedited grace period, if there were no readers, the
task will awaken itself.  This commit removes this useless self-awakening.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 34240697

kernel/rcutree.c

+1 −1
Original line number Diff line number Diff line
@@ -1320,7 +1320,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) 
	else

		raw_spin_unlock_irqrestore(&rnp->lock, flags);

	if (need_report & RCU_OFL_TASKS_EXP_GP)

		rcu_report_exp_rnp(rsp, rnp);

		rcu_report_exp_rnp(rsp, rnp, true);

	rcu_node_kthread_setaffinity(rnp, -1);

}

kernel/rcutree.h

+2 −1
Original line number Diff line number Diff line
@@ -444,7 +444,8 @@ static void rcu_preempt_check_callbacks(int cpu); 
static void rcu_preempt_process_callbacks(void);

void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));

#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)

static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);

static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,

			       bool wake);

#endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */

static int rcu_preempt_pending(int cpu);

static int rcu_preempt_needs_cpu(int cpu);

kernel/rcutree_plugin.h

+11 −5
Original line number Diff line number Diff line
@@ -410,7 +410,7 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) 
		 * then we need to report up the rcu_node hierarchy.

		 */

		if (!empty_exp && empty_exp_now)

			rcu_report_exp_rnp(&rcu_preempt_state, rnp);

			rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);

	} else {

		local_irq_restore(flags);

	}
@@ -732,9 +732,13 @@ static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) 
 * recursively up the tree.  (Calm down, calm down, we do the recursion

 * iteratively!)

 *

 * Most callers will set the "wake" flag, but the task initiating the

 * expedited grace period need not wake itself.

 *

 * Caller must hold sync_rcu_preempt_exp_mutex.

 */

static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)

static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,

			       bool wake)

{

	unsigned long flags;

	unsigned long mask;
@@ -747,6 +751,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) 
		}

		if (rnp->parent == NULL) {

			raw_spin_unlock_irqrestore(&rnp->lock, flags);

			if (wake)

				wake_up(&sync_rcu_preempt_exp_wq);

			break;

		}
@@ -780,7 +785,7 @@ sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) 
		must_wait = 1;

	}

	if (!must_wait)

		rcu_report_exp_rnp(rsp, rnp);

		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */

}



/*
@@ -1072,7 +1077,8 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); 
 * report on tasks preempted in RCU read-side critical sections during

 * expedited RCU grace periods.

 */

static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)

static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,

			       bool wake)

{

	return;

}