spinlock: lockbreak cleanup
The break_lock data structure and code for spinlocks is quite nasty.
Not only does it double the size of a spinlock but it changes locking to
a potentially less optimal trylock.
Put all of that under CONFIG_GENERIC_LOCKBREAK, and introduce a
__raw_spin_is_contended that uses the lock data itself to determine whether
there are waiters on the lock, to be used if CONFIG_GENERIC_LOCKBREAK is
not set.
Rename need_lockbreak to spin_needbreak, make it use spin_is_contended to
decouple it from the spinlock implementation, and make it typesafe (rwlocks
do not have any need_lockbreak sites -- why do they even get bloated up
with that break_lock then?).
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2d0546e..9d47976 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1922,23 +1922,16 @@
/*
* Does a critical section need to be broken due to another
- * task waiting?:
+ * task waiting?: (technically does not depend on CONFIG_PREEMPT,
+ * but a general need for low latency)
*/
-#if defined(CONFIG_PREEMPT) && defined(CONFIG_SMP)
-# define need_lockbreak(lock) ((lock)->break_lock)
-#else
-# define need_lockbreak(lock) 0
-#endif
-
-/*
- * Does a critical section need to be broken due to another
- * task waiting or preemption being signalled:
- */
-static inline int lock_need_resched(spinlock_t *lock)
+static inline int spin_needbreak(spinlock_t *lock)
{
- if (need_lockbreak(lock) || need_resched())
- return 1;
+#ifdef CONFIG_PREEMPT
+ return spin_is_contended(lock);
+#else
return 0;
+#endif
}
/*
diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index c376f3b..1244497 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -120,6 +120,12 @@
#define spin_is_locked(lock) __raw_spin_is_locked(&(lock)->raw_lock)
+#ifdef CONFIG_GENERIC_LOCKBREAK
+#define spin_is_contended(lock) ((lock)->break_lock)
+#else
+#define spin_is_contended(lock) __raw_spin_is_contended(&(lock)->raw_lock)
+#endif
+
/**
* spin_unlock_wait - wait until the spinlock gets unlocked
* @lock: the spinlock in question.
diff --git a/include/linux/spinlock_types.h b/include/linux/spinlock_types.h
index f6a3a95..68d88f7 100644
--- a/include/linux/spinlock_types.h
+++ b/include/linux/spinlock_types.h
@@ -19,7 +19,7 @@
typedef struct {
raw_spinlock_t raw_lock;
-#if defined(CONFIG_PREEMPT) && defined(CONFIG_SMP)
+#ifdef CONFIG_GENERIC_LOCKBREAK
unsigned int break_lock;
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
@@ -35,7 +35,7 @@
typedef struct {
raw_rwlock_t raw_lock;
-#if defined(CONFIG_PREEMPT) && defined(CONFIG_SMP)
+#ifdef CONFIG_GENERIC_LOCKBREAK
unsigned int break_lock;
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
diff --git a/include/linux/spinlock_up.h b/include/linux/spinlock_up.h
index ea54c4c..938234c 100644
--- a/include/linux/spinlock_up.h
+++ b/include/linux/spinlock_up.h
@@ -64,6 +64,8 @@
# define __raw_spin_trylock(lock) ({ (void)(lock); 1; })
#endif /* DEBUG_SPINLOCK */
+#define __raw_spin_is_contended(lock) (((void)(lock), 0))
+
#define __raw_read_can_lock(lock) (((void)(lock), 1))
#define __raw_write_can_lock(lock) (((void)(lock), 1))