[PATCH 07/13] rtmutex: Turn the plist into an rb-tree

From: Peter Zijlstra
Date: Tue Dec 17 2013 - 07:47:01 EST

Turn the pi-chains from plist to rb-tree, in the rt_mutex code,
and provide a proper comparison function for -deadline and
-priority tasks.

This is done mainly because:
- classical prio field of the plist is just an int, which might
not be enough for representing a deadline;
- manipulating such a list would become O(nr_deadline_tasks),
which might be to much, as the number of -deadline task increases.

Therefore, an rb-tree is used, and tasks are queued in it according
to the following logic:
- among two -priority (i.e., SCHED_BATCH/OTHER/RR/FIFO) tasks, the
one with the higher (lower, actually!) prio wins;
- among a -priority and a -deadline task, the latter always wins;
- among two -deadline tasks, the one with the earliest deadline
wins.

Queueing and dequeueing functions are changed accordingly, for both
the list of a task's pi-waiters and the list of tasks blocked on
a pi-lock.

Cc: nicola.manica@xxxxxxxxxxxxx
Cc: darren@xxxxxxxxxx
Cc: oleg@xxxxxxxxxx
Cc: dhaval.giani@xxxxxxxxx
Cc: paulmck@xxxxxxxxxxxxxxxxxx
Cc: fchecconi@xxxxxxxxx
Cc: fweisbec@xxxxxxxxx
Cc: harald.gustafsson@xxxxxxxxxxxx
Cc: hgu1972@xxxxxxxxx
Cc: insop.song@xxxxxxxxx
Cc: p.faure@xxxxxxxxxx
Cc: jkacur@xxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: johan.eker@xxxxxxxxxxxx
Cc: tglx@xxxxxxxxxxxxx
Cc: liming.wang@xxxxxxxxxxxxx
Cc: tommaso.cucinotta@xxxxxxxx
Cc: luca.abeni@xxxxxxxx
Cc: vincent.guittot@xxxxxxxxxx
Cc: michael@xxxxxxxxxxxxxxxxxxxx
Cc: bruce.ashfield@xxxxxxxxxxxxx
Cc: mingo@xxxxxxxxxx
Cc: claudio@xxxxxxxxxxxxxxx
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Dario Faggioli <raistlin@xxxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
include/linux/init_task.h | 10 ++
include/linux/rtmutex.h | 18 +---
include/linux/sched.h | 4 -
kernel/fork.c | 3
kernel/futex.c | 2
kernel/locking/rtmutex-debug.c | 8 --
kernel/locking/rtmutex.c | 151 ++++++++++++++++++++++++++++++++--------
kernel/locking/rtmutex_common.h | 22 ++---
kernel/sched/core.c | 4 -
9 files changed, 157 insertions(+), 65 deletions(-)

--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -11,6 +11,7 @@
#include <linux/user_namespace.h>
#include <linux/securebits.h>
#include <linux/seqlock.h>
+#include <linux/rbtree.h>
#include <net/net_namespace.h>
#include <linux/sched/rt.h>

@@ -154,6 +155,14 @@ extern struct task_group root_task_group

#define INIT_TASK_COMM "swapper"

+#ifdef CONFIG_RT_MUTEXES
+# define INIT_RT_MUTEXES(tsk) \
+ .pi_waiters = RB_ROOT, \
+ .pi_waiters_leftmost = NULL,
+#else
+# define INIT_RT_MUTEXES(tsk)
+#endif
+
/*
* INIT_TASK is used to set up the first task table, touch at
* your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -221,6 +230,7 @@ extern struct task_group root_task_group
INIT_TRACE_RECURSION \
INIT_TASK_RCU_PREEMPT(tsk) \
INIT_CPUSET_SEQ(tsk) \
+ INIT_RT_MUTEXES(tsk) \
INIT_VTIME(tsk) \
}

--- a/include/linux/rtmutex.h
+++ b/include/linux/rtmutex.h
@@ -13,7 +13,7 @@
#define __LINUX_RT_MUTEX_H

#include <linux/linkage.h>
-#include <linux/plist.h>
+#include <linux/rbtree.h>
#include <linux/spinlock_types.h>

extern int max_lock_depth; /* for sysctl */
@@ -22,12 +22,14 @@ extern int max_lock_depth; /* for sysctl
* The rt_mutex structure
*
* @wait_lock: spinlock to protect the structure
- * @wait_list: pilist head to enqueue waiters in priority order
+ * @waiters: rbtree root to enqueue waiters in priority order
+ * @waiters_leftmost: top waiter
* @owner: the mutex owner
*/
struct rt_mutex {
raw_spinlock_t wait_lock;
- struct plist_head wait_list;
+ struct rb_root waiters;
+ struct rb_node *waiters_leftmost;
struct task_struct *owner;
#ifdef CONFIG_DEBUG_RT_MUTEXES
int save_state;
@@ -66,7 +68,7 @@ struct hrtimer_sleeper;

#define __RT_MUTEX_INITIALIZER(mutexname) \
{ .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(mutexname.wait_lock) \
- , .wait_list = PLIST_HEAD_INIT(mutexname.wait_list) \
+ , .waiters = RB_ROOT \
, .owner = NULL \
__DEBUG_RT_MUTEX_INITIALIZER(mutexname)}

@@ -98,12 +100,4 @@ extern int rt_mutex_trylock(struct rt_mu

extern void rt_mutex_unlock(struct rt_mutex *lock);

-#ifdef CONFIG_RT_MUTEXES
-# define INIT_RT_MUTEXES(tsk) \
- .pi_waiters = PLIST_HEAD_INIT(tsk.pi_waiters), \
- INIT_RT_MUTEX_DEBUG(tsk)
-#else
-# define INIT_RT_MUTEXES(tsk)
-#endif
-
#endif
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -16,6 +16,7 @@ struct sched_param {
#include <linux/types.h>
#include <linux/timex.h>
#include <linux/jiffies.h>
+#include <linux/plist.h>
#include <linux/rbtree.h>
#include <linux/thread_info.h>
#include <linux/cpumask.h>
@@ -1346,7 +1347,8 @@ struct task_struct {

#ifdef CONFIG_RT_MUTEXES
/* PI waiters blocked on a rt_mutex held by this task */
- struct plist_head pi_waiters;
+ struct rb_root pi_waiters;
+ struct rb_node *pi_waiters_leftmost;
/* Deadlock detection and priority inheritance handling */
struct rt_mutex_waiter *pi_blocked_on;
#endif
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1086,7 +1086,8 @@ static void rt_mutex_init_task(struct ta
{
raw_spin_lock_init(&p->pi_lock);
#ifdef CONFIG_RT_MUTEXES
- plist_head_init(&p->pi_waiters);
+ p->pi_waiters = RB_ROOT;
+ p->pi_waiters_leftmost = NULL;
p->pi_blocked_on = NULL;
#endif
}
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2315,6 +2315,8 @@ static int futex_wait_requeue_pi(u32 __u
* code while we sleep on uaddr.
*/
debug_rt_mutex_init_waiter(&rt_waiter);
+ RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
+ RB_CLEAR_NODE(&rt_waiter.tree_entry);
rt_waiter.task = NULL;

ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
--- a/kernel/locking/rtmutex-debug.c
+++ b/kernel/locking/rtmutex-debug.c
@@ -24,7 +24,7 @@
#include <linux/kallsyms.h>
#include <linux/syscalls.h>
#include <linux/interrupt.h>
-#include <linux/plist.h>
+#include <linux/rbtree.h>
#include <linux/fs.h>
#include <linux/debug_locks.h>

@@ -57,7 +57,7 @@ static void printk_lock(struct rt_mutex

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

@@ -154,16 +154,12 @@ void debug_rt_mutex_proxy_unlock(struct
void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
{
memset(waiter, 0x11, sizeof(*waiter));
- plist_node_init(&waiter->list_entry, MAX_PRIO);
- plist_node_init(&waiter->pi_list_entry, MAX_PRIO);
waiter->deadlock_task_pid = NULL;
}

void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
{
put_pid(waiter->deadlock_task_pid);
- DEBUG_LOCKS_WARN_ON(!plist_node_empty(&waiter->list_entry));
- DEBUG_LOCKS_WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
memset(waiter, 0x22, sizeof(*waiter));
}

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -14,6 +14,7 @@
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/sched/rt.h>
+#include <linux/sched/deadline.h>
#include <linux/timer.h>

#include "rtmutex_common.h"
@@ -91,10 +92,104 @@ static inline void mark_rt_mutex_waiters
}
#endif

+static inline int
+rt_mutex_waiter_less(struct rt_mutex_waiter *left,
+ struct rt_mutex_waiter *right)
+{
+ if (left->task->prio < right->task->prio)
+ return 1;
+
+ /*
+ * If both tasks are dl_task(), we check their deadlines.
+ */
+ if (dl_prio(left->task->prio) && dl_prio(right->task->prio))
+ return (left->task->dl.deadline < right->task->dl.deadline);
+
+ return 0;
+}
+
+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 *parent = NULL;
+ struct rt_mutex_waiter *entry;
+ int leftmost = 1;
+
+ while (*link) {
+ parent = *link;
+ entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
+ if (rt_mutex_waiter_less(waiter, entry)) {
+ link = &parent->rb_left;
+ } else {
+ link = &parent->rb_right;
+ leftmost = 0;
+ }
+ }
+
+ if (leftmost)
+ lock->waiters_leftmost = &waiter->tree_entry;
+
+ rb_link_node(&waiter->tree_entry, parent, link);
+ rb_insert_color(&waiter->tree_entry, &lock->waiters);
+}
+
+static void
+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_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 *parent = NULL;
+ struct rt_mutex_waiter *entry;
+ int leftmost = 1;
+
+ while (*link) {
+ parent = *link;
+ entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
+ if (rt_mutex_waiter_less(waiter, entry)) {
+ link = &parent->rb_left;
+ } else {
+ link = &parent->rb_right;
+ leftmost = 0;
+ }
+ }
+
+ 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);
+}
+
+static void
+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_CLEAR_NODE(&waiter->pi_tree_entry);
+}
+
/*
- * Calculate task priority from the waiter list priority
+ * Calculate task priority from the waiter tree priority
*
- * Return task->normal_prio when the waiter list is empty or when
+ * Return task->normal_prio when the waiter tree is empty or when
* the waiter is not allowed to do priority boosting
*/
int rt_mutex_getprio(struct task_struct *task)
@@ -102,7 +197,7 @@ int rt_mutex_getprio(struct task_struct
if (likely(!task_has_pi_waiters(task)))
return task->normal_prio;

- return min(task_top_pi_waiter(task)->pi_list_entry.prio,
+ return min(task_top_pi_waiter(task)->task->prio,
task->normal_prio);
}

@@ -233,7 +328,7 @@ static int rt_mutex_adjust_prio_chain(st
* When deadlock detection is off then we check, if further
* priority adjustment is necessary.
*/
- if (!detect_deadlock && waiter->list_entry.prio == task->prio)
+ if (!detect_deadlock && waiter->task->prio == task->prio)
goto out_unlock_pi;

lock = waiter->lock;
@@ -254,9 +349,9 @@ static int rt_mutex_adjust_prio_chain(st
top_waiter = rt_mutex_top_waiter(lock);

/* Requeue the waiter */
- plist_del(&waiter->list_entry, &lock->wait_list);
- waiter->list_entry.prio = task->prio;
- plist_add(&waiter->list_entry, &lock->wait_list);
+ rt_mutex_dequeue(lock, waiter);
+ waiter->task->prio = task->prio;
+ rt_mutex_enqueue(lock, waiter);

/* Release the task */
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
@@ -280,17 +375,15 @@ static int rt_mutex_adjust_prio_chain(st

if (waiter == rt_mutex_top_waiter(lock)) {
/* Boost the owner */
- plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
- waiter->pi_list_entry.prio = waiter->list_entry.prio;
- plist_add(&waiter->pi_list_entry, &task->pi_waiters);
+ rt_mutex_dequeue_pi(task, top_waiter);
+ rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);

} else if (top_waiter == waiter) {
/* Deboost the owner */
- plist_del(&waiter->pi_list_entry, &task->pi_waiters);
+ rt_mutex_dequeue_pi(task, waiter);
waiter = rt_mutex_top_waiter(lock);
- waiter->pi_list_entry.prio = waiter->list_entry.prio;
- plist_add(&waiter->pi_list_entry, &task->pi_waiters);
+ rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);
}

@@ -355,7 +448,7 @@ static int try_to_take_rt_mutex(struct r
* 3) it is top waiter
*/
if (rt_mutex_has_waiters(lock)) {
- if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) {
+ if (task->prio >= rt_mutex_top_waiter(lock)->task->prio) {
if (!waiter || waiter != rt_mutex_top_waiter(lock))
return 0;
}
@@ -369,7 +462,7 @@ static int try_to_take_rt_mutex(struct r

/* remove the queued waiter. */
if (waiter) {
- plist_del(&waiter->list_entry, &lock->wait_list);
+ rt_mutex_dequeue(lock, waiter);
task->pi_blocked_on = NULL;
}

@@ -379,8 +472,7 @@ static int try_to_take_rt_mutex(struct r
*/
if (rt_mutex_has_waiters(lock)) {
top = rt_mutex_top_waiter(lock);
- top->pi_list_entry.prio = top->list_entry.prio;
- plist_add(&top->pi_list_entry, &task->pi_waiters);
+ rt_mutex_enqueue_pi(task, top);
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
}
@@ -416,13 +508,11 @@ static int task_blocks_on_rt_mutex(struc
__rt_mutex_adjust_prio(task);
waiter->task = task;
waiter->lock = lock;
- plist_node_init(&waiter->list_entry, task->prio);
- plist_node_init(&waiter->pi_list_entry, task->prio);

/* Get the top priority waiter on the lock */
if (rt_mutex_has_waiters(lock))
top_waiter = rt_mutex_top_waiter(lock);
- plist_add(&waiter->list_entry, &lock->wait_list);
+ rt_mutex_enqueue(lock, waiter);

task->pi_blocked_on = waiter;

@@ -433,8 +523,8 @@ static int task_blocks_on_rt_mutex(struc

if (waiter == rt_mutex_top_waiter(lock)) {
raw_spin_lock_irqsave(&owner->pi_lock, flags);
- plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
- plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
+ rt_mutex_dequeue_pi(owner, top_waiter);
+ rt_mutex_enqueue_pi(owner, waiter);

__rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on)
@@ -486,7 +576,7 @@ static void wakeup_next_waiter(struct rt
* boosted mode and go back to normal after releasing
* lock->wait_lock.
*/
- plist_del(&waiter->pi_list_entry, &current->pi_waiters);
+ rt_mutex_dequeue_pi(current, waiter);

rt_mutex_set_owner(lock, NULL);

@@ -510,7 +600,7 @@ static void remove_waiter(struct rt_mute
int chain_walk = 0;

raw_spin_lock_irqsave(&current->pi_lock, flags);
- plist_del(&waiter->list_entry, &lock->wait_list);
+ rt_mutex_dequeue(lock, waiter);
current->pi_blocked_on = NULL;
raw_spin_unlock_irqrestore(&current->pi_lock, flags);

@@ -521,13 +611,13 @@ static void remove_waiter(struct rt_mute

raw_spin_lock_irqsave(&owner->pi_lock, flags);

- plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
+ rt_mutex_dequeue_pi(owner, waiter);

if (rt_mutex_has_waiters(lock)) {
struct rt_mutex_waiter *next;

next = rt_mutex_top_waiter(lock);
- plist_add(&next->pi_list_entry, &owner->pi_waiters);
+ rt_mutex_enqueue_pi(owner, next);
}
__rt_mutex_adjust_prio(owner);

@@ -537,8 +627,6 @@ static void remove_waiter(struct rt_mute
raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
}

- WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
-
if (!chain_walk)
return;

@@ -565,7 +653,7 @@ void rt_mutex_adjust_pi(struct task_stru
raw_spin_lock_irqsave(&task->pi_lock, flags);

waiter = task->pi_blocked_on;
- if (!waiter || waiter->list_entry.prio == task->prio) {
+ if (!waiter || waiter->task->prio == task->prio) {
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
return;
}
@@ -638,6 +726,8 @@ rt_mutex_slowlock(struct rt_mutex *lock,
int ret = 0;

debug_rt_mutex_init_waiter(&waiter);
+ RB_CLEAR_NODE(&waiter.pi_tree_entry);
+ RB_CLEAR_NODE(&waiter.tree_entry);

raw_spin_lock(&lock->wait_lock);

@@ -904,7 +994,8 @@ void __rt_mutex_init(struct rt_mutex *lo
{
lock->owner = NULL;
raw_spin_lock_init(&lock->wait_lock);
- plist_head_init(&lock->wait_list);
+ lock->waiters = RB_ROOT;
+ lock->waiters_leftmost = NULL;

debug_rt_mutex_init(lock, name);
}
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -40,13 +40,13 @@ extern void schedule_rt_mutex_test(struc
* This is the control structure for tasks blocked on a rt_mutex,
* which is allocated on the kernel stack on of the blocked task.
*
- * @list_entry: pi node to enqueue into the mutex waiters list
- * @pi_list_entry: pi node to enqueue into the mutex owner waiters list
+ * @tree_entry: pi node to enqueue into the mutex waiters tree
+ * @pi_tree_entry: pi node to enqueue into the mutex owner waiters tree
* @task: task reference to the blocked task
*/
struct rt_mutex_waiter {
- struct plist_node list_entry;
- struct plist_node pi_list_entry;
+ struct rb_node tree_entry;
+ struct rb_node pi_tree_entry;
struct task_struct *task;
struct rt_mutex *lock;
#ifdef CONFIG_DEBUG_RT_MUTEXES
@@ -57,11 +57,11 @@ struct rt_mutex_waiter {
};

/*
- * Various helpers to access the waiters-plist:
+ * Various helpers to access the waiters-tree:
*/
static inline int rt_mutex_has_waiters(struct rt_mutex *lock)
{
- return !plist_head_empty(&lock->wait_list);
+ return !RB_EMPTY_ROOT(&lock->waiters);
}

static inline struct rt_mutex_waiter *
@@ -69,8 +69,8 @@ rt_mutex_top_waiter(struct rt_mutex *loc
{
struct rt_mutex_waiter *w;

- w = plist_first_entry(&lock->wait_list, struct rt_mutex_waiter,
- list_entry);
+ w = rb_entry(lock->waiters_leftmost, struct rt_mutex_waiter,
+ tree_entry);
BUG_ON(w->lock != lock);

return w;
@@ -78,14 +78,14 @@ rt_mutex_top_waiter(struct rt_mutex *loc

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

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

/*
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6625,10 +6625,6 @@ void __init sched_init(void)
INIT_HLIST_HEAD(&init_task.preempt_notifiers);
#endif

-#ifdef CONFIG_RT_MUTEXES
- plist_head_init(&init_task.pi_waiters);
-#endif
-
/*
* The boot idle thread does lazy MMU switching as well:
*/


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