diff options
| -rw-r--r-- | arch/mn10300/Kconfig | 11 | ||||
| -rw-r--r-- | include/linux/hardirq.h | 18 | ||||
| -rw-r--r-- | kernel/sched.c | 27 | ||||
| -rw-r--r-- | lib/kernel_lock.c | 120 |
4 files changed, 95 insertions, 81 deletions
diff --git a/arch/mn10300/Kconfig b/arch/mn10300/Kconfig index 6a6409a..e856218 100644 --- a/arch/mn10300/Kconfig +++ b/arch/mn10300/Kconfig @@ -186,17 +186,6 @@ config PREEMPT Say Y here if you are building a kernel for a desktop, embedded or real-time system. Say N if you are unsure. -config PREEMPT_BKL - bool "Preempt The Big Kernel Lock" - depends on PREEMPT - default y - help - This option reduces the latency of the kernel by making the - big kernel lock preemptible. - - Say Y here if you are building a kernel for a desktop system. - Say N if you are unsure. - config MN10300_CURRENT_IN_E2 bool "Hold current task address in E2 register" default y diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index 897f723..181006c 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -72,6 +72,14 @@ #define in_softirq() (softirq_count()) #define in_interrupt() (irq_count()) +#if defined(CONFIG_PREEMPT) +# define PREEMPT_INATOMIC_BASE kernel_locked() +# define PREEMPT_CHECK_OFFSET 1 +#else +# define PREEMPT_INATOMIC_BASE 0 +# define PREEMPT_CHECK_OFFSET 0 +#endif + /* * Are we running in atomic context? WARNING: this macro cannot * always detect atomic context; in particular, it cannot know about @@ -79,17 +87,11 @@ * used in the general case to determine whether sleeping is possible. * Do not use in_atomic() in driver code. */ -#define in_atomic() ((preempt_count() & ~PREEMPT_ACTIVE) != 0) - -#ifdef CONFIG_PREEMPT -# define PREEMPT_CHECK_OFFSET 1 -#else -# define PREEMPT_CHECK_OFFSET 0 -#endif +#define in_atomic() ((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_INATOMIC_BASE) /* * Check whether we were atomic before we did preempt_disable(): - * (used by the scheduler) + * (used by the scheduler, *after* releasing the kernel lock) */ #define in_atomic_preempt_off() \ ((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET) diff --git a/kernel/sched.c b/kernel/sched.c index 58fb8af..c51b656 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -4567,8 +4567,6 @@ EXPORT_SYMBOL(schedule); asmlinkage void __sched preempt_schedule(void) { struct thread_info *ti = current_thread_info(); - struct task_struct *task = current; - int saved_lock_depth; /* * If there is a non-zero preempt_count or interrupts are disabled, @@ -4579,16 +4577,7 @@ asmlinkage void __sched preempt_schedule(void) do { add_preempt_count(PREEMPT_ACTIVE); - - /* - * We keep the big kernel semaphore locked, but we - * clear ->lock_depth so that schedule() doesnt - * auto-release the semaphore: - */ - saved_lock_depth = task->lock_depth; - task->lock_depth = -1; schedule(); - task->lock_depth = saved_lock_depth; sub_preempt_count(PREEMPT_ACTIVE); /* @@ -4609,26 +4598,15 @@ EXPORT_SYMBOL(preempt_schedule); asmlinkage void __sched preempt_schedule_irq(void) { struct thread_info *ti = current_thread_info(); - struct task_struct *task = current; - int saved_lock_depth; /* Catch callers which need to be fixed */ BUG_ON(ti->preempt_count || !irqs_disabled()); do { add_preempt_count(PREEMPT_ACTIVE); - - /* - * We keep the big kernel semaphore locked, but we - * clear ->lock_depth so that schedule() doesnt - * auto-release the semaphore: - */ - saved_lock_depth = task->lock_depth; - task->lock_depth = -1; local_irq_enable(); schedule(); local_irq_disable(); - task->lock_depth = saved_lock_depth; sub_preempt_count(PREEMPT_ACTIVE); /* @@ -5853,8 +5831,11 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu) spin_unlock_irqrestore(&rq->lock, flags); /* Set the preempt count _outside_ the spinlocks! */ +#if defined(CONFIG_PREEMPT) + task_thread_info(idle)->preempt_count = (idle->lock_depth >= 0); +#else task_thread_info(idle)->preempt_count = 0; - +#endif /* * The idle tasks have their own, simple scheduling class: */ diff --git a/lib/kernel_lock.c b/lib/kernel_lock.c index cd3e825..01a3c22 100644 --- a/lib/kernel_lock.c +++ b/lib/kernel_lock.c @@ -11,79 +11,121 @@ #include <linux/semaphore.h> /* - * The 'big kernel semaphore' + * The 'big kernel lock' * - * This mutex is taken and released recursively by lock_kernel() + * This spinlock is taken and released recursively by lock_kernel() * and unlock_kernel(). It is transparently dropped and reacquired * over schedule(). It is used to protect legacy code that hasn't * been migrated to a proper locking design yet. * - * Note: code locked by this semaphore will only be serialized against - * other code using the same locking facility. The code guarantees that - * the task remains on the same CPU. - * * Don't use in new code. */ -static DECLARE_MUTEX(kernel_sem); +static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kernel_flag); + /* - * Re-acquire the kernel semaphore. + * Acquire/release the underlying lock from the scheduler. * - * This function is called with preemption off. + * This is called with preemption disabled, and should + * return an error value if it cannot get the lock and + * TIF_NEED_RESCHED gets set. * - * We are executing in schedule() so the code must be extremely careful - * about recursion, both due to the down() and due to the enabling of - * preemption. schedule() will re-check the preemption flag after - * reacquiring the semaphore. + * If it successfully gets the lock, it should increment + * the preemption count like any spinlock does. + * + * (This works on UP too - _raw_spin_trylock will never + * return false in that case) */ int __lockfunc __reacquire_kernel_lock(void) { - struct task_struct *task = current; - int saved_lock_depth = task->lock_depth; - - BUG_ON(saved_lock_depth < 0); - - task->lock_depth = -1; - preempt_enable_no_resched(); - - down(&kernel_sem); - + while (!_raw_spin_trylock(&kernel_flag)) { + if (test_thread_flag(TIF_NEED_RESCHED)) + return -EAGAIN; + cpu_relax(); + } preempt_disable(); - task->lock_depth = saved_lock_depth; - return 0; } void __lockfunc __release_kernel_lock(void) { - up(&kernel_sem); + _raw_spin_unlock(&kernel_flag); + preempt_enable_no_resched(); } /* - * Getting the big kernel semaphore. + * These are the BKL spinlocks - we try to be polite about preemption. + * If SMP is not on (ie UP preemption), this all goes away because the + * _raw_spin_trylock() will always succeed. */ -void __lockfunc lock_kernel(void) +#ifdef CONFIG_PREEMPT +static inline void __lock_kernel(void) { - struct task_struct *task = current; - int depth = task->lock_depth + 1; + preempt_disable(); + if (unlikely(!_raw_spin_trylock(&kernel_flag))) { + /* + * If preemption was disabled even before this + * was called, there's nothing we can be polite + * about - just spin. + */ + if (preempt_count() > 1) { + _raw_spin_lock(&kernel_flag); + return; + } - if (likely(!depth)) /* - * No recursion worries - we set up lock_depth _after_ + * Otherwise, let's wait for the kernel lock + * with preemption enabled.. */ - down(&kernel_sem); + do { + preempt_enable(); + while (spin_is_locked(&kernel_flag)) + cpu_relax(); + preempt_disable(); + } while (!_raw_spin_trylock(&kernel_flag)); + } +} - task->lock_depth = depth; +#else + +/* + * Non-preemption case - just get the spinlock + */ +static inline void __lock_kernel(void) +{ + _raw_spin_lock(&kernel_flag); } +#endif -void __lockfunc unlock_kernel(void) +static inline void __unlock_kernel(void) { - struct task_struct *task = current; + /* + * the BKL is not covered by lockdep, so we open-code the + * unlocking sequence (and thus avoid the dep-chain ops): + */ + _raw_spin_unlock(&kernel_flag); + preempt_enable(); +} - BUG_ON(task->lock_depth < 0); +/* + * Getting the big kernel lock. + * + * This cannot happen asynchronously, so we only need to + * worry about other CPU's. + */ +void __lockfunc lock_kernel(void) +{ + int depth = current->lock_depth+1; + if (likely(!depth)) + __lock_kernel(); + current->lock_depth = depth; +} - if (likely(--task->lock_depth < 0)) - up(&kernel_sem); +void __lockfunc unlock_kernel(void) +{ + BUG_ON(current->lock_depth < 0); + if (likely(--current->lock_depth < 0)) + __unlock_kernel(); } EXPORT_SYMBOL(lock_kernel); |
