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[RFC,tip/core/rcu,11/28] rcu: Omit self-awaken when setting up expedited grace period

Message ID 1320265849-5744-11-git-send-email-paulmck@linux.vnet.ibm.com
State New
Headers show

Commit Message

Paul E. McKenney Nov. 2, 2011, 8:30 p.m. UTC 
From: Thomas Gleixner <tglx@linutronix.de>

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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree.c        |    2 +-
 kernel/rcutree.h        |    3 ++-
 kernel/rcutree_plugin.h |   17 +++++++++++------
 3 files changed, 14 insertions(+), 8 deletions(-)

Comments

Josh Triplett Nov. 3, 2011, 3:16 a.m. UTC | #1 
On Wed, Nov 02, 2011 at 01:30:32PM -0700, Paul E. McKenney wrote:
> -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;
>  }

Removing this return represents a separate cleanup, which ought to go in
a separate commit.

- Josh Triplett
Paul E. McKenney Nov. 3, 2011, 7:43 p.m. UTC | #2 
On Wed, Nov 02, 2011 at 08:16:13PM -0700, Josh Triplett wrote:
> On Wed, Nov 02, 2011 at 01:30:32PM -0700, Paul E. McKenney wrote:
> > -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;
> >  }
> 
> Removing this return represents a separate cleanup, which ought to go in
> a separate commit.

I split this out.

							Thanx, Paul
diff mbox

Patch

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c097394..bbcafba 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -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);
 }
 
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 0963fa1..fd2f87d 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -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);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 708dc57..7a7961f 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -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;
@@ -747,7 +751,8 @@  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);
-			wake_up(&sync_rcu_preempt_exp_wq);
+			if (wake)
+				wake_up(&sync_rcu_preempt_exp_wq);
 			break;
 		}
 		mask = rnp->grpmask;
@@ -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. */
 }
 
 /*
@@ -1072,9 +1077,9 @@  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;
 }
 
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */