[PATCH 03/22] mutex: Use p->on_cpu for the adaptive spin

Peter Zijlstra
2011-03-02T17:42:53Z

[-- Attachment #1: sched-on_cpu-use.patch --]
[-- Type: text/plain, Size: 5902 bytes --]

Since we now have p->on_cpu unconditionally available, use it to
re-implement mutex_spin_on_owner.

Requested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
---
include/linux/mutex.h | 2 -
include/linux/sched.h | 2 -
kernel/mutex-debug.c | 2 -
kernel/mutex-debug.h | 2 -
kernel/mutex.c | 2 -
kernel/mutex.h | 2 -
kernel/sched.c | 83 +++++++++++++++++++-------------------------------
7 files changed, 39 insertions(+), 56 deletions(-)

Index: linux-2.6/include/linux/mutex.h
===================================================================
--- linux-2.6.orig/include/linux/mutex.h
+++ linux-2.6/include/linux/mutex.h
@@ -51,7 +51,7 @@ struct mutex {
spinlock_t wait_lock;
struct list_head wait_list;
#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
- struct thread_info *owner;
+ struct task_struct *owner;
#endif
#ifdef CONFIG_DEBUG_MUTEXES
const char *name;
Index: linux-2.6/kernel/mutex-debug.c
===================================================================
--- linux-2.6.orig/kernel/mutex-debug.c
+++ linux-2.6/kernel/mutex-debug.c
@@ -75,7 +75,7 @@ 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);
mutex_clear_owner(lock);
}
Index: linux-2.6/kernel/mutex-debug.h
===================================================================
--- linux-2.6.orig/kernel/mutex-debug.h
+++ linux-2.6/kernel/mutex-debug.h
@@ -29,7 +29,7 @@ extern void debug_mutex_init(struct mute

static inline void mutex_set_owner(struct mutex *lock)
{
- lock->owner = current_thread_info();
+ lock->owner = current;
}

static inline void mutex_clear_owner(struct mutex *lock)
Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c
+++ linux-2.6/kernel/mutex.c
@@ -160,7 +160,7 @@ __mutex_lock_common(struct mutex *lock,
*/

for (;;) {
- struct thread_info *owner;
+ struct task_struct *owner;

/*
* If we own the BKL, then don't spin. The owner of
Index: linux-2.6/kernel/mutex.h
===================================================================
--- linux-2.6.orig/kernel/mutex.h
+++ linux-2.6/kernel/mutex.h
@@ -19,7 +19,7 @@
#ifdef CONFIG_SMP
static inline void mutex_set_owner(struct mutex *lock)
{
- lock->owner = current_thread_info();
+ lock->owner = current;
}

static inline void mutex_clear_owner(struct mutex *lock)
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -4034,70 +4034,53 @@ asmlinkage void __sched schedule(void)
EXPORT_SYMBOL(schedule);

#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
-/*
- * Look out! "owner" is an entirely speculative pointer
- * access and not reliable.
- */
-int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
-{
- unsigned int cpu;
- struct rq *rq;

- if (!sched_feat(OWNER_SPIN))
- return 0;
+static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
+{
+ bool ret = false;

-#ifdef CONFIG_DEBUG_PAGEALLOC
- /*
- * Need to access the cpu field knowing that
- * DEBUG_PAGEALLOC could have unmapped it if
- * the mutex owner just released it and exited.
- */
- if (probe_kernel_address(&owner->cpu, cpu))
- return 0;
-#else
- cpu = owner->cpu;
-#endif
+ rcu_read_lock();
+ if (lock->owner != owner)
+ goto fail;

/*
- * Even if the access succeeded (likely case),
- * the cpu field may no longer be valid.
+ * Ensure we emit the owner->on_cpu, dereference _after_ checking
+ * lock->owner still matches owner, if that fails, owner might
+ * point to free()d memory, if it still matches, the rcu_read_lock()
+ * ensures the memory stays valid.
*/
- if (cpu >= nr_cpumask_bits)
- return 0;
+ barrier();

- /*
- * We need to validate that we can do a
- * get_cpu() and that we have the percpu area.
- */
- if (!cpu_online(cpu))
- return 0;
+ ret = owner->on_cpu;
+fail:
+ rcu_read_unlock();

- rq = cpu_rq(cpu);
+ return ret;
+}

- for (;;) {
- /*
- * Owner changed, break to re-assess state.
- */
- if (lock->owner != owner) {
- /*
- * If the lock has switched to a different owner,
- * we likely have heavy contention. Return 0 to quit
- * optimistic spinning and not contend further:
- */
- if (lock->owner)
- return 0;
- break;
- }
+/*
+ * Look out! "owner" is an entirely speculative pointer
+ * access and not reliable.
+ */
+int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
+{
+ if (!sched_feat(OWNER_SPIN))
+ return 0;

- /*
- * Is that owner really running on that cpu?
- */
- if (task_thread_info(rq->curr) != owner || need_resched())
+ while (owner_running(lock, owner)) {
+ if (need_resched())
return 0;

arch_mutex_cpu_relax();
}

+ /*
+ * If the owner changed to another task there is likely
+ * heavy contention, stop spinning.
+ */
+ if (lock->owner)
+ return 0;
+
return 1;
}
#endif
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -360,7 +360,7 @@ extern signed long schedule_timeout_inte
extern signed long schedule_timeout_killable(signed long timeout);
extern signed long schedule_timeout_uninterruptible(signed long timeout);
asmlinkage void schedule(void);
-extern int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner);
+extern int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner);

struct nsproxy;
struct user_namespace;