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rcu: refine structure rcu_node field for rcu boost

PATCH In review Liu, Changcheng 2 participants 3 messages Jan 18, 2018 – Jan 19, 2018 RCU

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Liu, Changcheng

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#0 lore raw

PATCH 1/1 rcu: refine structure rcu_node field for rcu boost

Do not allocate space for rcu boost field when
RCU BOOST is not configured.

Signed-off-by Liu Changcheng <[email protected]>
kernel/rcu/tree.h +3 -0
index 46a5d19..88f087e 100644
@@ -129,6 +129,7 @@ struct rcu_node {
 				/*  if there is no such task.  If there */
 				/*  is no current expedited grace period, */
 				/*  then there can cannot be any such task. */
+#ifdef CONFIG_RCU_BOOST
 	struct list_head *boost_tasks;
 				/* Pointer to first task that needs to be */
 				/*  priority boosted, or NULL if no priority */

@@ -153,6 +154,8 @@ struct rcu_node {
 				/* Number of tasks boosted for expedited GP. */
 	unsigned long n_normal_boosts;
 				/* Number of tasks boosted for normal GP. */
+#endif/* #ifdef CONFIG_RCU_BOOST*/
+
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */
kernel/rcu/tree_plugin.h +2 -0
index db85ca3..fee0b1e 100644
@@ -506,8 +506,10 @@ void rcu_read_unlock_special(struct task_struct *t)
 		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
 			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
 			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+#ifdef CONFIG_RCU_BOOST
 			if (&t->rcu_node_entry == rnp->boost_tasks)
 				rnp->boost_tasks = np;
+#endif
 		}
 
 		/*
Signature · 1 line
2.7.4
#1 lore raw
Quoted 4 lines · Changcheng

Do not allocate space for rcu boost field when
RCU BOOST is not configured.

Signed-off-by Liu Changcheng <[email protected]>

The added #ifdef in rcu_read_unlock_special() is a deal-breaker. Just out of curiosity, is this decrease in storage measurable at the system level?

Thanx, Paul

Quoted 39 lines
kernel/rcu/tree.h +3 -0
index 46a5d19..88f087e 100644
@@ -129,6 +129,7 @@ struct rcu_node {
 				/*  if there is no such task.  If there */
 				/*  is no current expedited grace period, */
 				/*  then there can cannot be any such task. */
+#ifdef CONFIG_RCU_BOOST
 	struct list_head *boost_tasks;
 				/* Pointer to first task that needs to be */
 				/*  priority boosted, or NULL if no priority */

@@ -153,6 +154,8 @@ struct rcu_node {
 				/* Number of tasks boosted for expedited GP. */
 	unsigned long n_normal_boosts;
 				/* Number of tasks boosted for normal GP. */
+#endif/* #ifdef CONFIG_RCU_BOOST*/
+
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */
kernel/rcu/tree_plugin.h +2 -0
index db85ca3..fee0b1e 100644
@@ -506,8 +506,10 @@ void rcu_read_unlock_special(struct task_struct *t)
 		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
 			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
 			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+#ifdef CONFIG_RCU_BOOST
 			if (&t->rcu_node_entry == rnp->boost_tasks)
 				rnp->boost_tasks = np;
+#endif
 		}
 
 		/*
Signature · 1 line
2.7.4
author
#2 lore raw

Hi Paul,
This patch is optional.

1. It's true that the added #ifdef in rcu_read_unlock_special is a bad breaker. The patch follows the current code e.g. CONFIG_PROVE_RCU

2. Haven't evaluated the performance in system. Studying RCU and found that boost feature field is allocated in in the rcu_node structure even rcu boost isn't enabled.

B.R.
Changcheng

Quoted 53 lines · Paul E. McKenney
Quoted 4 lines · Changcheng

Do not allocate space for rcu boost field when
RCU BOOST is not configured.

Signed-off-by Liu Changcheng <[email protected]>

The added #ifdef in rcu_read_unlock_special() is a deal-breaker. Just out of curiosity, is this decrease in storage measurable at the system level?

Thanx, Paul

Quoted 39 lines
kernel/rcu/tree.h +3 -0
index 46a5d19..88f087e 100644
@@ -129,6 +129,7 @@ struct rcu_node {
 				/*  if there is no such task.  If there */
 				/*  is no current expedited grace period, */
 				/*  then there can cannot be any such task. */
+#ifdef CONFIG_RCU_BOOST
 	struct list_head *boost_tasks;
 				/* Pointer to first task that needs to be */
 				/*  priority boosted, or NULL if no priority */

@@ -153,6 +154,8 @@ struct rcu_node {
 				/* Number of tasks boosted for expedited GP. */
 	unsigned long n_normal_boosts;
 				/* Number of tasks boosted for normal GP. */
+#endif/* #ifdef CONFIG_RCU_BOOST*/
+
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */
kernel/rcu/tree_plugin.h +2 -0
index db85ca3..fee0b1e 100644
@@ -506,8 +506,10 @@ void rcu_read_unlock_special(struct task_struct *t)
 		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
 			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
 			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+#ifdef CONFIG_RCU_BOOST
 			if (&t->rcu_node_entry == rnp->boost_tasks)
 				rnp->boost_tasks = np;
+#endif
 		}
 
 		/*
Signature · 1 line
2.7.4