[PATCH 4/9] locking/rtmutex: Replace top-waiter and pi_waiters leftmost caching

Davidlohr Bueso
2017-06-29T17:18:20Z

... with the generic rbtree flavor instead. No changes
in semantics whatsoever.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
include/linux/init_task.h | 5 ++---
include/linux/rtmutex.h | 11 +++++------
include/linux/sched.h | 3 +--
kernel/fork.c | 3 +--
kernel/locking/rtmutex-debug.c | 2 +-
kernel/locking/rtmutex.c | 35 +++++++++++------------------------
kernel/locking/rtmutex_common.h | 12 ++++++------
7 files changed, 27 insertions(+), 44 deletions(-)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 9fa5aae21c00..d0f23d50eb20 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -175,9 +175,8 @@ extern struct cred init_cred;

#ifdef CONFIG_RT_MUTEXES
# define INIT_RT_MUTEXES(tsk) \
- .pi_waiters = RB_ROOT, \
- .pi_top_task = NULL, \
- .pi_waiters_leftmost = NULL,
+ .pi_waiters = RB_ROOT_CACHED, \
+ .pi_top_task = NULL,
#else
# define INIT_RT_MUTEXES(tsk)
#endif
diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
index 44fd002f7cd5..53fcbe9de7fd 100644
--- a/include/linux/rtmutex.h
+++ b/include/linux/rtmutex.h
@@ -22,18 +22,17 @@ extern int max_lock_depth; /* for sysctl */
* The rt_mutex structure
*
* @wait_lock: spinlock to protect the structure
- * @waiters: rbtree root to enqueue waiters in priority order
- * @waiters_leftmost: top waiter
+ * @waiters: rbtree root to enqueue waiters in priority order;
+ * caches top-waiter (leftmost node).
* @owner: the mutex owner
*/
struct rt_mutex {
raw_spinlock_t wait_lock;
- struct rb_root waiters;
- struct rb_node *waiters_leftmost;
+ struct rb_root_cached waiters;
struct task_struct *owner;
#ifdef CONFIG_DEBUG_RT_MUTEXES
int save_state;
- const char *name, *file;
+ const char *name, *file;
int line;
void *magic;
#endif
@@ -84,7 +83,7 @@ do { \

#define __RT_MUTEX_INITIALIZER(mutexname) \
{ .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(mutexname.wait_lock) \
- , .waiters = RB_ROOT \
+ , .waiters = RB_ROOT_CACHED \
, .owner = NULL \
__DEBUG_RT_MUTEX_INITIALIZER(mutexname) \
__DEP_MAP_RT_MUTEX_INITIALIZER(mutexname)}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4e933f368cc0..5cb5d2e31c02 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -803,8 +803,7 @@ struct task_struct {

#ifdef CONFIG_RT_MUTEXES
/* PI waiters blocked on a rt_mutex held by this task: */
- struct rb_root pi_waiters;
- struct rb_node *pi_waiters_leftmost;
+ struct rb_root_cached pi_waiters;
/* Updated under owner's pi_lock and rq lock */
struct task_struct *pi_top_task;
/* Deadlock detection and priority inheritance handling: */
diff --git a/kernel/fork.c b/kernel/fork.c
index 05a4984fc044..8dcc63e8d9e6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1458,8 +1458,7 @@ static void rt_mutex_init_task(struct task_struct *p)
{
raw_spin_lock_init(&p->pi_lock);
#ifdef CONFIG_RT_MUTEXES
- p->pi_waiters = RB_ROOT;
- p->pi_waiters_leftmost = NULL;
+ p->pi_waiters = RB_ROOT_CACHED;
p->pi_top_task = NULL;
p->pi_blocked_on = NULL;
#endif
diff --git a/kernel/locking/rtmutex-debug.c b/kernel/locking/rtmutex-debug.c
index ac35e648b0e5..f4a74e78d467 100644
--- a/kernel/locking/rtmutex-debug.c
+++ b/kernel/locking/rtmutex-debug.c
@@ -58,7 +58,7 @@ static void printk_lock(struct rt_mutex *lock, int print_owner)

void rt_mutex_debug_task_free(struct task_struct *task)
{
- DEBUG_LOCKS_WARN_ON(!RB_EMPTY_ROOT(&task->pi_waiters));
+ DEBUG_LOCKS_WARN_ON(!RB_EMPTY_ROOT(&task->pi_waiters.rb_root));
DEBUG_LOCKS_WARN_ON(task->pi_blocked_on);
}

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 78069895032a..e40eee33174f 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -271,10 +271,10 @@ rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
static void
rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
{
- struct rb_node **link = &lock->waiters.rb_node;
+ struct rb_node **link = &lock->waiters.rb_root.rb_node;
struct rb_node *parent = NULL;
struct rt_mutex_waiter *entry;
- int leftmost = 1;
+ bool leftmost = true;

while (*link) {
parent = *link;
@@ -283,15 +283,12 @@ rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
link = &parent->rb_left;
} else {
link = &parent->rb_right;
- leftmost = 0;
+ leftmost = false;
}
}

- if (leftmost)
- lock->waiters_leftmost = &waiter->tree_entry;
-
rb_link_node(&waiter->tree_entry, parent, link);
- rb_insert_color(&waiter->tree_entry, &lock->waiters);
+ rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
}

static void
@@ -300,20 +297,17 @@ rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
if (RB_EMPTY_NODE(&waiter->tree_entry))
return;

- if (lock->waiters_leftmost == &waiter->tree_entry)
- lock->waiters_leftmost = rb_next(&waiter->tree_entry);
-
- rb_erase(&waiter->tree_entry, &lock->waiters);
+ rb_erase_cached(&waiter->tree_entry, &lock->waiters);
RB_CLEAR_NODE(&waiter->tree_entry);
}

static void
rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
{
- struct rb_node **link = &task->pi_waiters.rb_node;
+ struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
struct rb_node *parent = NULL;
struct rt_mutex_waiter *entry;
- int leftmost = 1;
+ bool leftmost = true;

while (*link) {
parent = *link;
@@ -322,15 +316,12 @@ rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
link = &parent->rb_left;
} else {
link = &parent->rb_right;
- leftmost = 0;
+ leftmost = false;
}
}

- if (leftmost)
- task->pi_waiters_leftmost = &waiter->pi_tree_entry;
-
rb_link_node(&waiter->pi_tree_entry, parent, link);
- rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
+ rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
}

static void
@@ -339,10 +330,7 @@ rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
return;

- if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
- task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
-
- rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
+ rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
RB_CLEAR_NODE(&waiter->pi_tree_entry);
}

@@ -1658,8 +1646,7 @@ void __rt_mutex_init(struct rt_mutex *lock, const char *name,
{
lock->owner = NULL;
raw_spin_lock_init(&lock->wait_lock);
- lock->waiters = RB_ROOT;
- lock->waiters_leftmost = NULL;
+ lock->waiters = RB_ROOT_CACHED;

if (name && key)
debug_rt_mutex_init(lock, name, key);
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 72ad45a9a794..524beeee24b0 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -42,7 +42,7 @@ struct rt_mutex_waiter {
*/
static inline int rt_mutex_has_waiters(struct rt_mutex *lock)
{
- return !RB_EMPTY_ROOT(&lock->waiters);
+ return !RB_EMPTY_ROOT(&lock->waiters.rb_root);
}

static inline struct rt_mutex_waiter *
@@ -50,8 +50,8 @@ rt_mutex_top_waiter(struct rt_mutex *lock)
{
struct rt_mutex_waiter *w;

- w = rb_entry(lock->waiters_leftmost, struct rt_mutex_waiter,
- tree_entry);
+ w = rb_entry(lock->waiters.rb_leftmost,
+ struct rt_mutex_waiter, tree_entry);
BUG_ON(w->lock != lock);

return w;
@@ -59,14 +59,14 @@ rt_mutex_top_waiter(struct rt_mutex *lock)

static inline int task_has_pi_waiters(struct task_struct *p)
{
- return !RB_EMPTY_ROOT(&p->pi_waiters);
+ return !RB_EMPTY_ROOT(&p->pi_waiters.rb_root);
}

static inline struct rt_mutex_waiter *
task_top_pi_waiter(struct task_struct *p)
{
- return rb_entry(p->pi_waiters_leftmost, struct rt_mutex_waiter,
- pi_tree_entry);
+ return rb_entry(p->pi_waiters.rb_leftmost,
+ struct rt_mutex_waiter, pi_tree_entry);
}

/*
--
2.12.0