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SubjectRe: [RFC][PATCH RT 1/3] locking: Add spin_try_or_boost_lock() infrastructure
On Thu, 03 Sep 2015 21:19:01 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> \
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 2822aceb8dfb..2830c17dc3e4 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -253,6 +253,65 @@ rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
> RB_CLEAR_NODE(&waiter->pi_tree_entry);
> }
>
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +static inline int task_normal_prio(struct task_struct *task)
> +{
> + return min(task->normal_prio, task->trylock_prio);
> +}
> +
> +static inline int task_top_waiter_prio(struct task_struct *task)
> +{
> + return min3(task_top_pi_waiter(task)->prio,
> + task->normal_prio, task->trylock_prio);
> +}
> +
> +static inline void clear_trylock_prio(struct task_struct *task)
> +{
> + task->trylock_prio = MAX_PRIO;
> +}
> +
> +static inline bool current_boosted(void)
> +{
> + return current->trylock_prio < MAX_PRIO;
> +}
> +
> +static void __rt_mutex_adjust_prio(struct task_struct *task);
> +
> +/* Must call rt_mutex_adjust_prio_chain() if an owner is returned */
> +static inline struct task_struct *trylock_boost_owner(struct rt_mutex *lock)
> +{
> + struct task_struct *owner;
> +
> + owner = rt_mutex_owner(lock);
> + if (!owner)
> + return NULL;
> +
> + /* Will be released by rt_mutex_adjust_prio_chain() */
> + get_task_struct(owner);
> +
> + raw_spin_lock_irq(&owner->pi_lock);
> + if (owner->trylock_prio > current->prio) {
> + owner->trylock_prio = current->prio;
> + __rt_mutex_adjust_prio(owner);
> + }
> + raw_spin_unlock_irq(&owner->pi_lock);
> +
> + return owner;
> +}
> +#else

I forgot to add:

static inline struct task_struct *trylock_boost_owner(struct rt_mutex *lock)
{
return NULL;
}

See, I didn't test the non PREEMPT_RT cases ;-)

-- Steve

> +static inline int task_normal_prio(struct task_struct *task)
> +{
> + return task->normal_prio;
> +}
> +static inline int task_top_waiter_prio(struct task_struct *task)
> +{
> + return min(task_top_pi_waiter(task)->prio,
> + task->normal_prio);
> +}
> +# define current_boosted() 0
> +# define clear_trylock_prio(tsk) do {} while (0)
> +#endif
> +



> @@ -1717,26 +1790,34 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
> /*
> * Slow path try-lock function:
> */
> -static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
> +static inline int rt_mutex_slowtrylock(struct rt_mutex *lock, bool boost)
> {
> + struct task_struct *owner;
> int ret;
>
> /*
> * If the lock already has an owner we fail to get the lock.
> * This can be done without taking the @lock->wait_lock as
> * it is only being read, and this is a trylock anyway.
> + *
> + * Only do the short cut if we do not need to boost the task
> + * if we fail to get the lock.
> */
> - if (rt_mutex_owner(lock))
> + if (!boost && rt_mutex_owner(lock))
> return 0;
>
> /*
> - * The mutex has currently no owner. Lock the wait lock and
> - * try to acquire the lock.
> + * The mutex has currently no owner or we need to boost the task
> + * if we fail to grab the lock. Lock the wait lock and try to
> + * acquire the lock.
> */
> raw_spin_lock(&lock->wait_lock);
>
> ret = try_to_take_rt_mutex(lock, current, NULL);
>
> + if (!ret && boost)
> + owner = trylock_boost_owner(lock);
> +
> /*
> * try_to_take_rt_mutex() sets the lock waiters bit
> * unconditionally. Clean this up.
> @@ -1745,6 +1826,10 @@ static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
>
> raw_spin_unlock(&lock->wait_lock);
>
> + if (!ret && boost && owner)
> + rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK,
> + lock, NULL, NULL, NULL);
> +
> return ret;
> }
>



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