As mentioned by Ingo, the SCHED_FEAT_OWNER_SPIN scheduler feature
bit was really just an early hack to make with/without mutex-spinning
testable. So it is no longer necessary.
This patch removes the SCHED_FEAT_OWNER_SPIN feature bit and move the
mutex spinning code from kernel/sched/core.c back to kernel/mutex.c
which is where they should belong.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
---
include/linux/sched.h | 4 ---
kernel/mutex.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++
kernel/sched/core.c | 63 -----------------------------------------------
kernel/sched/features.h | 7 -----
4 files changed, 62 insertions(+), 74 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8af6f13..aefe45d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -320,10 +320,6 @@ extern signed long schedule_timeout_killable(signed long timeout);
extern signed long schedule_timeout_uninterruptible(signed long timeout);
asmlinkage void schedule(void);
extern void schedule_preempt_disabled(void);
-#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
-extern int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner);
-extern int mutex_can_spin_on_owner(struct mutex *lock);
-#endif
struct nsproxy;
struct user_namespace;
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 140f113..ad53a66 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -158,6 +158,68 @@ static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node)
ACCESS_ONCE(next->locked) = 1;
smp_wmb();
}
+
+/*
+ * Mutex spinning code migrated from kernel/sched/core.c
+ */
+
+static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
+{
+ if (lock->owner != owner)
+ return false;
+
+ /*
+ * 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.
+ */
+ barrier();
+
+ return owner->on_cpu;
+}
+
+/*
+ * Look out! "owner" is an entirely speculative pointer
+ * access and not reliable.
+ */
+static noinline
+int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
+{
+ rcu_read_lock();
+ while (owner_running(lock, owner)) {
+ if (need_resched())
+ break;
+
+ arch_mutex_cpu_relax();
+ }
+ rcu_read_unlock();
+
+ /*
+ * We break out the loop above on need_resched() and when the
+ * owner changed, which is a sign for heavy contention. Return
+ * success only when lock->owner is NULL.
+ */
+ return lock->owner == NULL;
+}
+
+/*
+ * Initial check for entering the mutex spinning loop
+ */
+static inline int mutex_can_spin_on_owner(struct mutex *lock)
+{
+ int retval = 1;
+
+ rcu_read_lock();
+ if (lock->owner)
+ retval = lock->owner->on_cpu;
+ rcu_read_unlock();
+ /*
+ * if lock->owner is not set, the mutex owner may have just acquired
+ * it and not set the owner yet or the mutex has been released.
+ */
+ return retval;
+}
#endif
static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 176e82a..b37a22b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2997,69 +2997,6 @@ void __sched schedule_preempt_disabled(void)
preempt_disable();
}
-#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
-
-static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
-{
- if (lock->owner != owner)
- return false;
-
- /*
- * 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.
- */
- barrier();
-
- return owner->on_cpu;
-}
-
-/*
- * Look out! "owner" is an entirely speculative pointer
- * access and not reliable.
- */
-int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
-{
- rcu_read_lock();
- while (owner_running(lock, owner)) {
- if (need_resched())
- break;
-
- arch_mutex_cpu_relax();
- }
- rcu_read_unlock();
-
- /*
- * We break out the loop above on need_resched() and when the
- * owner changed, which is a sign for heavy contention. Return
- * success only when lock->owner is NULL.
- */
- return lock->owner == NULL;
-}
-
-/*
- * Initial check for entering the mutex spinning loop
- */
-int mutex_can_spin_on_owner(struct mutex *lock)
-{
- int retval = 1;
-
- if (!sched_feat(OWNER_SPIN))
- return 0;
-
- rcu_read_lock();
- if (lock->owner)
- retval = lock->owner->on_cpu;
- rcu_read_unlock();
- /*
- * if lock->owner is not set, the mutex owner may have just acquired
- * it and not set the owner yet or the mutex has been released.
- */
- return retval;
-}
-#endif
-
#ifdef CONFIG_PREEMPT
/*
* this is the entry point to schedule() from in-kernel preemption
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 1ad1d2b..99399f8 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -46,13 +46,6 @@ SCHED_FEAT(DOUBLE_TICK, false)
SCHED_FEAT(LB_BIAS, true)
/*
- * Spin-wait on mutex acquisition when the mutex owner is running on
- * another cpu -- assumes that when the owner is running, it will soon
- * release the lock. Decreases scheduling overhead.
- */
-SCHED_FEAT(OWNER_SPIN, true)
-
-/*
* Decrement CPU power based on time not spent running tasks
*/
SCHED_FEAT(NONTASK_POWER, true)
--
1.7.1
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