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Subject[PATCH RFC tip/core/rcu 11/28] rcu: Omit self-awaken when setting up expedited grace period
Date
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(-)
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 */
--
1.7.3.2


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