rtmutex: Turn the plist into an rb-tree
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.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dario Faggioli <raistlin@linux.it>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-again-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-10-git-send-email-juri.lelli@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
index de17134..3aed8d7 100644
--- 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 @@
* 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 @@
#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 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