PSN-EDF: re-implement FMLP support

Implement the partitioned FMLP with priority boosting based on the
generic lock API.

2 files changed, 251 insertions, 6 deletions

diff --git a/litmus/locking.c b/litmus/locking.c
index ab643475093f..d39afaeefffe 100644
--- a/litmus/locking.c
+++ b/litmus/locking.c
@@ -108,6 +108,19 @@ asmlinkage long sys_litmus_unlock(int lock_od)
         return err;
 }
 
+struct task_struct* waitqueue_first(wait_queue_head_t *wq)
+{
+        wait_queue_t *q;
+
+        if (waitqueue_active(wq)) {
+                q = list_entry(wq->task_list.next,
+                               wait_queue_t, task_list);
+                return (struct task_struct*) q->private;
+        } else
+                return NULL;
+}
+
+
 #else
 
 struct fdso_ops generic_lock_ops = {};
diff --git a/litmus/sched_psn_edf.c b/litmus/sched_psn_edf.c
index fc64c1722ae9..801bc92c5835 100644
--- a/litmus/sched_psn_edf.c
+++ b/litmus/sched_psn_edf.c
@@ -71,6 +71,66 @@ static void preempt(psnedf_domain_t *pedf)
         preempt_if_preemptable(pedf->scheduled, pedf->cpu);
 }
 
+#ifdef CONFIG_LITMUS_LOCKING
+
+static void boost_priority(struct task_struct* t)
+{
+        unsigned long           flags;
+        psnedf_domain_t*        pedf = task_pedf(t);
+        lt_t                    now;
+
+        raw_spin_lock_irqsave(&pedf->slock, flags);
+        now = litmus_clock();
+
+        TRACE_TASK(t, "priority boosted at %llu\n", now);
+
+        tsk_rt(t)->priority_boosted = 1;
+        tsk_rt(t)->boost_start_time = now;
+
+        if (pedf->scheduled != t) {
+                /* holder may be queued: first stop queue changes */
+                raw_spin_lock(&pedf->domain.release_lock);
+                if (is_queued(t) &&
+                    /* If it is queued, then we need to re-order. */
+                    bheap_decrease(edf_ready_order, tsk_rt(t)->heap_node) &&
+                    /* If we bubbled to the top, then we need to check for preemptions. */
+                    edf_preemption_needed(&pedf->domain, pedf->scheduled))
+                                preempt(pedf);
+                raw_spin_unlock(&pedf->domain.release_lock);
+        } /* else: nothing to do since the job is not queued while scheduled */
+
+        raw_spin_unlock_irqrestore(&pedf->slock, flags);
+}
+
+static void unboost_priority(struct task_struct* t)
+{
+        unsigned long           flags;
+        psnedf_domain_t*        pedf = task_pedf(t);
+        lt_t                    now;
+
+        raw_spin_lock_irqsave(&pedf->slock, flags);
+        now = litmus_clock();
+
+        /* assumption: this only happens when the job is scheduled */
+        BUG_ON(pedf->scheduled != t);
+
+        TRACE_TASK(t, "priority restored at %llu\n", now);
+
+        /* priority boosted jobs must be scheduled */
+        BUG_ON(pedf->scheduled != t);
+
+        tsk_rt(t)->priority_boosted = 0;
+        tsk_rt(t)->boost_start_time = 0;
+
+        /* check if this changes anything */
+        if (edf_preemption_needed(&pedf->domain, pedf->scheduled))
+                preempt(pedf);
+
+        raw_spin_unlock_irqrestore(&pedf->slock, flags);
+}
+
+#endif
+
 /* This check is trivial in partioned systems as we only have to consider
  * the CPU of the partition.
  */
@@ -252,15 +312,16 @@ static void psnedf_task_wake_up(struct task_struct *task)
         TRACE_TASK(task, "wake_up at %llu\n", litmus_clock());
         raw_spin_lock_irqsave(&pedf->slock, flags);
         BUG_ON(is_queued(task));
+        now = litmus_clock();
+        if (is_tardy(task, now)
+#ifdef CONFIG_LITMUS_LOCKING
         /* We need to take suspensions because of semaphores into
          * account! If a job resumes after being suspended due to acquiring
          * a semaphore, it should never be treated as a new job release.
-         *
-         * FIXME: This should be done in some more predictable and userspace-controlled way.
          */
-        now = litmus_clock();
-        if (is_tardy(task, now) &&
-            get_rt_flags(task) != RT_F_EXIT_SEM) {
+            && !is_priority_boosted(task)
+#endif
+                ) {
                 /* new sporadic release */
                 release_at(task, now);
                 sched_trace_task_release(task);
@@ -314,6 +375,8 @@ static void psnedf_task_exit(struct task_struct * t)
 #include <litmus/fdso.h>
 #include <litmus/srp.h>
 
+/* ******************** SRP support ************************ */
+
 static unsigned int psnedf_get_srp_prio(struct task_struct* t)
 {
         /* assumes implicit deadlines */
@@ -326,14 +389,183 @@ static long psnedf_activate_plugin(void)
         return 0;
 }
 
+/* ******************** FMLP support ********************** */
+
+/* struct for semaphore with priority inheritance */
+struct fmlp_semaphore {
+        struct litmus_lock litmus_lock;
+
+        /* current resource holder */
+        struct task_struct *owner;
+
+        /* FIFO queue of waiting tasks */
+        wait_queue_head_t wait;
+};
+
+static inline struct fmlp_semaphore* fmlp_from_lock(struct litmus_lock* lock)
+{
+        return container_of(lock, struct fmlp_semaphore, litmus_lock);
+}
+int psnedf_fmlp_lock(struct litmus_lock* l)
+{
+        struct task_struct* t = current;
+        struct fmlp_semaphore *sem = fmlp_from_lock(l);
+        wait_queue_t wait;
+        unsigned long flags;
+
+        if (!is_realtime(t))
+                return -EPERM;
+
+        spin_lock_irqsave(&sem->wait.lock, flags);
+
+        if (sem->owner) {
+                /* resource is not free => must suspend and wait */
+
+                init_waitqueue_entry(&wait, t);
+
+                /* FIXME: interruptible would be nice some day */
+                set_task_state(t, TASK_UNINTERRUPTIBLE);
+
+                __add_wait_queue_tail_exclusive(&sem->wait, &wait);
+
+                /* release lock before sleeping */
+                spin_unlock_irqrestore(&sem->wait.lock, flags);
+
+                /* We depend on the FIFO order.  Thus, we don't need to recheck
+                 * when we wake up; we are guaranteed to have the lock since
+                 * there is only one wake up per release.
+                 */
+
+                schedule();
+
+                /* Since we hold the lock, no other task will change
+                 * ->owner. We can thus check it without acquiring the spin
+                 * lock. */
+                BUG_ON(sem->owner != t);
+
+                /* FIXME: could we punt the dequeuing to the previous job,
+                 * which is holding the spinlock anyway? */
+                remove_wait_queue(&sem->wait, &wait);
+        } else {
+                /* it's ours now */
+                sem->owner = t;
+
+                /* mark the task as priority-boosted. */
+                boost_priority(t);
+
+                spin_unlock_irqrestore(&sem->wait.lock, flags);
+        }
+
+        return 0;
+}
+
+int psnedf_fmlp_unlock(struct litmus_lock* l)
+{
+        struct task_struct *t = current, *next;
+        struct fmlp_semaphore *sem = fmlp_from_lock(l);
+        unsigned long flags;
+        int err = 0;
+
+        spin_lock_irqsave(&sem->wait.lock, flags);
+
+        if (sem->owner != t) {
+                err = -EINVAL;
+                goto out;
+        }
+
+        /* we lose the benefit of priority boosting */
+
+        unboost_priority(t);
+
+        /* check if there are jobs waiting for this resource */
+        next = waitqueue_first(&sem->wait);
+        if (next) {
+                /* boost next job */
+                boost_priority(next);
+
+                /* next becomes the resouce holder */
+                sem->owner = next;
+
+                /* wake up next */
+                wake_up_process(next);
+        } else
+                /* resource becomes available */
+                sem->owner = NULL;
+
+out:
+        spin_unlock_irqrestore(&sem->wait.lock, flags);
+        return err;
+}
+
+int psnedf_fmlp_close(struct litmus_lock* l)
+{
+        struct task_struct *t = current;
+        struct fmlp_semaphore *sem = fmlp_from_lock(l);
+        unsigned long flags;
+
+        int owner;
+
+        spin_lock_irqsave(&sem->wait.lock, flags);
+
+        owner = sem->owner == t;
+
+        spin_unlock_irqrestore(&sem->wait.lock, flags);
+
+        if (owner)
+                psnedf_fmlp_unlock(l);
+
+        return 0;
+}
+
+void psnedf_fmlp_free(struct litmus_lock* lock)
+{
+        kfree(fmlp_from_lock(lock));
+}
+
+static struct litmus_lock_ops psnedf_fmlp_lock_ops = {
+        .close  = psnedf_fmlp_close,
+        .lock   = psnedf_fmlp_lock,
+        .unlock = psnedf_fmlp_unlock,
+        .deallocate = psnedf_fmlp_free,
+};
+
+static struct litmus_lock* psnedf_new_fmlp(void)
+{
+        struct fmlp_semaphore* sem;
+
+        sem = kmalloc(sizeof(*sem), GFP_KERNEL);
+        if (!sem)
+                return NULL;
+
+        sem->owner   = NULL;
+        init_waitqueue_head(&sem->wait);
+        sem->litmus_lock.ops = &psnedf_fmlp_lock_ops;
+
+        return &sem->litmus_lock;
+}
+
+/* **** lock constructor **** */
+
+
 static long psnedf_allocate_lock(struct litmus_lock **lock, int type)
 {
         int err = -ENXIO;
         struct srp_semaphore* srp;
 
+        /* PSN-EDF currently supports the SRP for local resources and the FMLP
+         * for global resources. */
         switch (type) {
+        case FMLP_SEM:
+                /* Flexible Multiprocessor Locking Protocol */
+                *lock = psnedf_new_fmlp();
+                if (*lock)
+                        err = 0;
+                else
+                        err = -ENOMEM;
+                break;
+
         case SRP_SEM:
-                /* Baker's SRP */
+                /* Baker's Stack Resource Policy */
                 srp = allocate_srp_semaphore();
                 if (srp) {
                         *lock = &srp->litmus_lock;