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Subject[PATCH][RFC]: mutex: adaptive spin
From
Date
Subject: mutex: adaptive spin
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Tue Jan 06 12:32:12 CET 2009

Based on the code in -rt, provide adaptive spins on generic mutexes.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/mutex.h | 4 ++--
include/linux/sched.h | 1 +
kernel/mutex-debug.c | 11 ++---------
kernel/mutex-debug.h | 8 --------
kernel/mutex.c | 46 +++++++++++++++++++++++++++++++++++++++-------
kernel/mutex.h | 2 --
kernel/sched.c | 5 +++++
7 files changed, 49 insertions(+), 28 deletions(-)
Index: linux-2.6/include/linux/mutex.h
===================================================================
--- linux-2.6.orig/include/linux/mutex.h
+++ linux-2.6/include/linux/mutex.h
@@ -50,8 +50,8 @@ struct mutex {
atomic_t count;
spinlock_t wait_lock;
struct list_head wait_list;
+ struct task_struct *owner;
#ifdef CONFIG_DEBUG_MUTEXES
- struct thread_info *owner;
const char *name;
void *magic;
#endif
@@ -67,8 +67,8 @@ struct mutex {
struct mutex_waiter {
struct list_head list;
struct task_struct *task;
-#ifdef CONFIG_DEBUG_MUTEXES
struct mutex *lock;
+#ifdef CONFIG_DEBUG_MUTEXES
void *magic;
#endif
};
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -249,6 +249,7 @@ extern void init_idle(struct task_struct
extern void init_idle_bootup_task(struct task_struct *idle);

extern int runqueue_is_locked(void);
+extern int task_is_current(struct task_struct *p);
extern void task_rq_unlock_wait(struct task_struct *p);

extern cpumask_var_t nohz_cpu_mask;
Index: linux-2.6/kernel/mutex-debug.c
===================================================================
--- linux-2.6.orig/kernel/mutex-debug.c
+++ linux-2.6/kernel/mutex-debug.c
@@ -26,11 +26,6 @@
/*
* Must be called with lock->wait_lock held.
*/
-void debug_mutex_set_owner(struct mutex *lock, struct thread_info *new_owner)
-{
- lock->owner = new_owner;
-}
-
void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
{
memset(waiter, MUTEX_DEBUG_INIT, sizeof(*waiter));
@@ -59,7 +54,6 @@ void debug_mutex_add_waiter(struct mutex

/* Mark the current thread as blocked on the lock: */
ti->task->blocked_on = waiter;
- waiter->lock = lock;
}

void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
@@ -80,9 +74,9 @@ void debug_mutex_unlock(struct mutex *lo
return;

DEBUG_LOCKS_WARN_ON(lock->magic != lock);
- DEBUG_LOCKS_WARN_ON(lock->owner != current_thread_info());
+ DEBUG_LOCKS_WARN_ON(lock->owner != current);
DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
- DEBUG_LOCKS_WARN_ON(lock->owner != current_thread_info());
+ DEBUG_LOCKS_WARN_ON(lock->owner != current);
}

void debug_mutex_init(struct mutex *lock, const char *name,
@@ -95,7 +89,6 @@ void debug_mutex_init(struct mutex *lock
debug_check_no_locks_freed((void *)lock, sizeof(*lock));
lockdep_init_map(&lock->dep_map, name, key, 0);
#endif
- lock->owner = NULL;
lock->magic = lock;
}

Index: linux-2.6/kernel/mutex-debug.h
===================================================================
--- linux-2.6.orig/kernel/mutex-debug.h
+++ linux-2.6/kernel/mutex-debug.h
@@ -13,14 +13,6 @@
/*
* This must be called with lock->wait_lock held.
*/
-extern void
-debug_mutex_set_owner(struct mutex *lock, struct thread_info *new_owner);
-
-static inline void debug_mutex_clear_owner(struct mutex *lock)
-{
- lock->owner = NULL;
-}
-
extern void debug_mutex_lock_common(struct mutex *lock,
struct mutex_waiter *waiter);
extern void debug_mutex_wake_waiter(struct mutex *lock,
Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c
+++ linux-2.6/kernel/mutex.c
@@ -46,6 +46,7 @@ __mutex_init(struct mutex *lock, const c
atomic_set(&lock->count, 1);
spin_lock_init(&lock->wait_lock);
INIT_LIST_HEAD(&lock->wait_list);
+ lock->owner = NULL;

debug_mutex_init(lock, name, key);
}
@@ -120,6 +121,28 @@ void __sched mutex_unlock(struct mutex *

EXPORT_SYMBOL(mutex_unlock);

+#ifdef CONFIG_SMP
+static int adaptive_wait(struct mutex_waiter *waiter,
+ struct task_struct *owner, long state)
+{
+ for (;;) {
+ if (signal_pending_state(state, waiter->task))
+ return 0;
+ if (waiter->lock->owner != owner)
+ return 0;
+ if (!task_is_current(owner))
+ return 1;
+ cpu_relax();
+ }
+}
+#else
+static int adaptive_wait(struct mutex_waiter *waiter,
+ struct task_struct *owner, long state)
+{
+ return 1;
+}
+#endif
+
/*
* Lock a mutex (possibly interruptible), slowpath:
*/
@@ -127,7 +150,7 @@ static inline int __sched
__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
unsigned long ip)
{
- struct task_struct *task = current;
+ struct task_struct *owner, *task = current;
struct mutex_waiter waiter;
unsigned int old_val;
unsigned long flags;
@@ -141,6 +164,7 @@ __mutex_lock_common(struct mutex *lock,
/* add waiting tasks to the end of the waitqueue (FIFO): */
list_add_tail(&waiter.list, &lock->wait_list);
waiter.task = task;
+ waiter.lock = lock;

old_val = atomic_xchg(&lock->count, -1);
if (old_val == 1)
@@ -175,11 +199,19 @@ __mutex_lock_common(struct mutex *lock,
debug_mutex_free_waiter(&waiter);
return -EINTR;
}
- __set_task_state(task, state);

- /* didnt get the lock, go to sleep: */
+ owner = lock->owner;
+ get_task_struct(owner);
spin_unlock_mutex(&lock->wait_lock, flags);
- schedule();
+
+ if (adaptive_wait(&waiter, owner, state)) {
+ put_task_struct(owner);
+ __set_task_state(task, state);
+ /* didnt get the lock, go to sleep: */
+ schedule();
+ } else
+ put_task_struct(owner);
+
spin_lock_mutex(&lock->wait_lock, flags);
}

@@ -187,7 +219,7 @@ done:
lock_acquired(&lock->dep_map, ip);
/* got the lock - rejoice! */
mutex_remove_waiter(lock, &waiter, task_thread_info(task));
- debug_mutex_set_owner(lock, task_thread_info(task));
+ lock->owner = task;

/* set it to 0 if there are no waiters left: */
if (likely(list_empty(&lock->wait_list)))
@@ -260,7 +292,7 @@ __mutex_unlock_common_slowpath(atomic_t
wake_up_process(waiter->task);
}

- debug_mutex_clear_owner(lock);
+ lock->owner = NULL;

spin_unlock_mutex(&lock->wait_lock, flags);
}
@@ -352,7 +384,7 @@ static inline int __mutex_trylock_slowpa

prev = atomic_xchg(&lock->count, -1);
if (likely(prev == 1)) {
- debug_mutex_set_owner(lock, current_thread_info());
+ lock->owner = current;
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
}
/* Set it back to 0 if there are no waiters: */
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -697,6 +697,11 @@ int runqueue_is_locked(void)
return ret;
}

+int task_is_current(struct task_struct *p)
+{
+ return task_rq(p)->curr == p;
+}
+
/*
* Debugging: various feature bits
*/
Index: linux-2.6/kernel/mutex.h
===================================================================
--- linux-2.6.orig/kernel/mutex.h
+++ linux-2.6/kernel/mutex.h
@@ -16,8 +16,6 @@
#define mutex_remove_waiter(lock, waiter, ti) \
__list_del((waiter)->list.prev, (waiter)->list.next)

-#define debug_mutex_set_owner(lock, new_owner) do { } while (0)
-#define debug_mutex_clear_owner(lock) do { } while (0)
#define debug_mutex_wake_waiter(lock, waiter) do { } while (0)
#define debug_mutex_free_waiter(waiter) do { } while (0)
#define debug_mutex_add_waiter(lock, waiter, ti) do { } while (0)


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