[ported from 2008.3] Add GSN-EDF plugin

- insert arm_release_timer() in add_relese() path
- arm_release_timer() uses __hrtimer_start_range_ns() instead of
  hrtimer_start() to avoid deadlock on rq->lock.

4 files changed, 856 insertions, 18 deletions

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index ec1de97600e7..337ce0c44f92 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -22,6 +22,9 @@
 #include <linux/interrupt.h>
 #include <linux/cpu.h>
 
+#include <litmus/litmus.h>
+#include <litmus/trace.h>
+
 #include <asm/mtrr.h>
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
@@ -117,6 +120,7 @@ static void native_smp_send_reschedule(int cpu)
                 WARN_ON(1);
                 return;
         }
+        TS_SEND_RESCHED_START(cpu);
         apic->send_IPI_mask(cpumask_of(cpu), RESCHEDULE_VECTOR);
 }
 
@@ -197,7 +201,12 @@ static void native_smp_send_stop(void)
 void smp_reschedule_interrupt(struct pt_regs *regs)
 {
         ack_APIC_irq();
+        /* LITMUS^RT needs this interrupt to proper reschedule
+         * on this cpu
+         */
+        set_tsk_need_resched(current);
         inc_irq_stat(irq_resched_count);
+        TS_SEND_RESCHED_END;
         /*
          * KVM uses this interrupt to force a cpu out of guest mode
          */
diff --git a/litmus/Makefile b/litmus/Makefile
index 0720c95918af..b15e65ee7f37 100644
--- a/litmus/Makefile
+++ b/litmus/Makefile
@@ -10,7 +10,8 @@ obj-y     = sched_plugin.o litmus.o \
             fdso.o \
             srp.o \
             fmlp.o \
-            heap.o
+            heap.o \
+            sched_gsn_edf.o
 
 obj-$(CONFIG_FEATHER_TRACE) += ft_event.o ftdev.o
 obj-$(CONFIG_SCHED_TASK_TRACE) += sched_task_trace.o
diff --git a/litmus/rt_domain.c b/litmus/rt_domain.c
index 4fa834018efa..78e76421aeba 100644
--- a/litmus/rt_domain.c
+++ b/litmus/rt_domain.c
@@ -159,23 +159,23 @@ static void reinit_release_heap(struct task_struct* t)
         /* initialize */
         heap_init(&rh->heap);
 }
-
-static void arm_release_timer(unsigned long _rt)
+/* arm_release_timer() - start local release timer or trigger
+ *     remote timer (pull timer)
+ *
+ * Called by add_release() with:
+ * - tobe_lock taken
+ * - IRQ disabled
+ */
+static void arm_release_timer(rt_domain_t *_rt)
 {
-        rt_domain_t *rt = (rt_domain_t*) _rt;
-        unsigned long flags;
+        rt_domain_t *rt = _rt;
         struct list_head list;
         struct list_head *pos, *safe;
         struct task_struct* t;
         struct release_heap* rh;
 
-        /* We only have to defend against the ISR since norq callbacks
-         * are serialized.
-         */
         TRACE("arm_release_timer() at %llu\n", litmus_clock());
-        spin_lock_irqsave(&rt->tobe_lock, flags);
         list_replace_init(&rt->tobe_released, &list);
-        spin_unlock_irqrestore(&rt->tobe_lock, flags);
 
         list_for_each_safe(pos, safe, &list) {
                 /* pick task of work list */
@@ -184,24 +184,29 @@ static void arm_release_timer(unsigned long _rt)
                 list_del(pos);
 
                 /* put into release heap while holding release_lock */
-                spin_lock_irqsave(&rt->release_lock, flags);
+                spin_lock(&rt->release_lock);
                 TRACE_TASK(t, "I have the release_lock 0x%p\n", &rt->release_lock);
+
                 rh = get_release_heap(rt, t, 0);
                 if (!rh) {
                         /* need to use our own, but drop lock first */
                         spin_unlock(&rt->release_lock);
                         TRACE_TASK(t, "Dropped release_lock 0x%p\n",
                                    &rt->release_lock);
+
                         reinit_release_heap(t);
                         TRACE_TASK(t, "release_heap ready\n");
+
                         spin_lock(&rt->release_lock);
                         TRACE_TASK(t, "Re-acquired release_lock 0x%p\n",
                                    &rt->release_lock);
+
                         rh = get_release_heap(rt, t, 1);
                 }
                 heap_insert(rt->order, &rh->heap, tsk_rt(t)->heap_node);
                 TRACE_TASK(t, "arm_release_timer(): added to release heap\n");
-                spin_unlock_irqrestore(&rt->release_lock, flags);
+
+                spin_unlock(&rt->release_lock);
                 TRACE_TASK(t, "Returned the release_lock 0x%p\n", &rt->release_lock);
 
                 /* To avoid arming the timer multiple times, we only let the
@@ -210,9 +215,16 @@ static void arm_release_timer(unsigned long _rt)
                  */
                 if (rh == tsk_rt(t)->rel_heap) {
                         TRACE_TASK(t, "arming timer 0x%p\n", &rh->timer);
-                        hrtimer_start(&rh->timer,
-                                      ns_to_ktime(rh->release_time),
-                                      HRTIMER_MODE_ABS);
+                        /* we cannot arm the timer using hrtimer_start()
+                         * as it may deadlock on rq->lock
+                         */
+                        /* FIXME now only one cpu without pulling
+                         * later more cpus; hrtimer_pull should call
+                         * __hrtimer_start... always with PINNED mode
+                         */
+                        __hrtimer_start_range_ns(&rh->timer,
+                                        ns_to_ktime(rh->release_time),
+                                        0, HRTIMER_MODE_ABS_PINNED, 0);
                 } else
                         TRACE_TASK(t, "0x%p is not my timer\n", &rh->timer);
         }
@@ -280,8 +292,8 @@ void __add_release(rt_domain_t* rt, struct task_struct *task)
         TRACE_TASK(task, "add_release(), rel=%llu\n", get_release(task));
         list_add(&tsk_rt(task)->list, &rt->tobe_released);
         task->rt_param.domain = rt;
-        /* XXX arm_release_timer() used to be activated here
-         *     such that it would be called with the runqueue lock dropped.
-         */
+
+        /* start release timer */
+        arm_release_timer(rt);
 }
 
diff --git a/litmus/sched_gsn_edf.c b/litmus/sched_gsn_edf.c
new file mode 100644
index 000000000000..69990805e16a
--- /dev/null
+++ b/litmus/sched_gsn_edf.c
@@ -0,0 +1,816 @@
+/*
+ * litmus/sched_gsn_edf.c
+ *
+ * Implementation of the GSN-EDF scheduling algorithm.
+ *
+ * This version uses the simple approach and serializes all scheduling
+ * decisions by the use of a queue lock. This is probably not the
+ * best way to do it, but it should suffice for now.
+ */
+
+#include <linux/spinlock.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+
+#include <litmus/litmus.h>
+#include <litmus/jobs.h>
+#include <litmus/sched_plugin.h>
+#include <litmus/edf_common.h>
+#include <litmus/sched_trace.h>
+
+#include <litmus/heap.h>
+
+#include <linux/module.h>
+
+/* Overview of GSN-EDF operations.
+ *
+ * For a detailed explanation of GSN-EDF have a look at the FMLP paper. This
+ * description only covers how the individual operations are implemented in
+ * LITMUS.
+ *
+ * link_task_to_cpu(T, cpu)     - Low-level operation to update the linkage
+ *                                structure (NOT the actually scheduled
+ *                                task). If there is another linked task To
+ *                                already it will set To->linked_on = NO_CPU
+ *                                (thereby removing its association with this
+ *                                CPU). However, it will not requeue the
+ *                                previously linked task (if any). It will set
+ *                                T's state to RT_F_RUNNING and check whether
+ *                                it is already running somewhere else. If T
+ *                                is scheduled somewhere else it will link
+ *                                it to that CPU instead (and pull the linked
+ *                                task to cpu). T may be NULL.
+ *
+ * unlink(T)                    - Unlink removes T from all scheduler data
+ *                                structures. If it is linked to some CPU it
+ *                                will link NULL to that CPU. If it is
+ *                                currently queued in the gsnedf queue it will
+ *                                be removed from the rt_domain. It is safe to
+ *                                call unlink(T) if T is not linked. T may not
+ *                                be NULL.
+ *
+ * requeue(T)                   - Requeue will insert T into the appropriate
+ *                                queue. If the system is in real-time mode and
+ *                                the T is released already, it will go into the
+ *                                ready queue. If the system is not in
+ *                                real-time mode is T, then T will go into the
+ *                                release queue. If T's release time is in the
+ *                                future, it will go into the release
+ *                                queue. That means that T's release time/job
+ *                                no/etc. has to be updated before requeu(T) is
+ *                                called. It is not safe to call requeue(T)
+ *                                when T is already queued. T may not be NULL.
+ *
+ * gsnedf_job_arrival(T)        - This is the catch all function when T enters
+ *                                the system after either a suspension or at a
+ *                                job release. It will queue T (which means it
+ *                                is not safe to call gsnedf_job_arrival(T) if
+ *                                T is already queued) and then check whether a
+ *                                preemption is necessary. If a preemption is
+ *                                necessary it will update the linkage
+ *                                accordingly and cause scheduled to be called
+ *                                (either with an IPI or need_resched). It is
+ *                                safe to call gsnedf_job_arrival(T) if T's
+ *                                next job has not been actually released yet
+ *                                (releast time in the future). T will be put
+ *                                on the release queue in that case.
+ *
+ * job_completion(T)            - Take care of everything that needs to be done
+ *                                to prepare T for its next release and place
+ *                                it in the right queue with
+ *                                gsnedf_job_arrival().
+ *
+ *
+ * When we now that T is linked to CPU then link_task_to_cpu(NULL, CPU) is
+ * equivalent to unlink(T). Note that if you unlink a task from a CPU none of
+ * the functions will automatically propagate pending task from the ready queue
+ * to a linked task. This is the job of the calling function ( by means of
+ * __take_ready).
+ */
+
+
+/* cpu_entry_t - maintain the linked and scheduled state
+ */
+typedef struct  {
+        int                     cpu;
+        struct task_struct*     linked;         /* only RT tasks */
+        struct task_struct*     scheduled;      /* only RT tasks */
+        atomic_t                will_schedule;  /* prevent unneeded IPIs */
+        struct heap_node*       hn;
+} cpu_entry_t;
+DEFINE_PER_CPU(cpu_entry_t, gsnedf_cpu_entries);
+
+cpu_entry_t* gsnedf_cpus[NR_CPUS];
+
+#define set_will_schedule() \
+        (atomic_set(&__get_cpu_var(gsnedf_cpu_entries).will_schedule, 1))
+#define clear_will_schedule() \
+        (atomic_set(&__get_cpu_var(gsnedf_cpu_entries).will_schedule, 0))
+#define test_will_schedule(cpu) \
+        (atomic_read(&per_cpu(gsnedf_cpu_entries, cpu).will_schedule))
+
+
+/* the cpus queue themselves according to priority in here */
+static struct heap_node gsnedf_heap_node[NR_CPUS];
+static struct heap      gsnedf_cpu_heap;
+
+static rt_domain_t gsnedf;
+#define gsnedf_lock (gsnedf.ready_lock)
+
+
+static int cpu_lower_prio(struct heap_node *_a, struct heap_node *_b)
+{
+        cpu_entry_t *a, *b;
+        a = _a->value;
+        b = _b->value;
+        /* Note that a and b are inverted: we want the lowest-priority CPU at
+         * the top of the heap.
+         */
+        return edf_higher_prio(b->linked, a->linked);
+}
+
+/* update_cpu_position - Move the cpu entry to the correct place to maintain
+ *                       order in the cpu queue. Caller must hold gsnedf lock.
+ */
+static void update_cpu_position(cpu_entry_t *entry)
+{
+        if (likely(heap_node_in_heap(entry->hn)))
+                heap_delete(cpu_lower_prio, &gsnedf_cpu_heap, entry->hn);
+        heap_insert(cpu_lower_prio, &gsnedf_cpu_heap, entry->hn);
+}
+
+/* caller must hold gsnedf lock */
+static cpu_entry_t* lowest_prio_cpu(void)
+{
+        struct heap_node* hn;
+        hn = heap_peek(cpu_lower_prio, &gsnedf_cpu_heap);
+        return hn->value;
+}
+
+
+/* link_task_to_cpu - Update the link of a CPU.
+ *                    Handles the case where the to-be-linked task is already
+ *                    scheduled on a different CPU.
+ */
+static noinline void link_task_to_cpu(struct task_struct* linked,
+                                      cpu_entry_t *entry)
+{
+        cpu_entry_t *sched;
+        struct task_struct* tmp;
+        int on_cpu;
+
+        BUG_ON(linked && !is_realtime(linked));
+
+        /* Currently linked task is set to be unlinked. */
+        if (entry->linked) {
+                entry->linked->rt_param.linked_on = NO_CPU;
+        }
+
+        /* Link new task to CPU. */
+        if (linked) {
+                set_rt_flags(linked, RT_F_RUNNING);
+                /* handle task is already scheduled somewhere! */
+                on_cpu = linked->rt_param.scheduled_on;
+                if (on_cpu != NO_CPU) {
+                        sched = &per_cpu(gsnedf_cpu_entries, on_cpu);
+                        /* this should only happen if not linked already */
+                        BUG_ON(sched->linked == linked);
+
+                        /* If we are already scheduled on the CPU to which we
+                         * wanted to link, we don't need to do the swap --
+                         * we just link ourselves to the CPU and depend on
+                         * the caller to get things right.
+                         */
+                        if (entry != sched) {
+                                TRACE_TASK(linked,
+                                           "already scheduled on %d, updating link.\n",
+                                           sched->cpu);
+                                tmp = sched->linked;
+                                linked->rt_param.linked_on = sched->cpu;
+                                sched->linked = linked;
+                                update_cpu_position(sched);
+                                linked = tmp;
+                        }
+                }
+                if (linked) /* might be NULL due to swap */
+                        linked->rt_param.linked_on = entry->cpu;
+        }
+        entry->linked = linked;
+        if (linked)
+                TRACE_TASK(linked, "linked to %d.\n", entry->cpu);
+        else
+                TRACE("NULL linked to %d.\n", entry->cpu);
+        update_cpu_position(entry);
+}
+
+/* unlink - Make sure a task is not linked any longer to an entry
+ *          where it was linked before. Must hold gsnedf_lock.
+ */
+static noinline void unlink(struct task_struct* t)
+{
+        cpu_entry_t *entry;
+
+        if (unlikely(!t)) {
+                TRACE_BUG_ON(!t);
+                return;
+        }
+
+        if (t->rt_param.linked_on != NO_CPU) {
+                /* unlink */
+                entry = &per_cpu(gsnedf_cpu_entries, t->rt_param.linked_on);
+                t->rt_param.linked_on = NO_CPU;
+                link_task_to_cpu(NULL, entry);
+        } else if (is_queued(t)) {
+                /* This is an interesting situation: t is scheduled,
+                 * but was just recently unlinked.  It cannot be
+                 * linked anywhere else (because then it would have
+                 * been relinked to this CPU), thus it must be in some
+                 * queue. We must remove it from the list in this
+                 * case.
+                 */
+                remove(&gsnedf, t);
+        }
+}
+
+
+/* preempt - force a CPU to reschedule
+ */
+static noinline void preempt(cpu_entry_t *entry)
+{
+        /* We cannot make the is_np() decision here if it is a remote CPU
+         * because requesting exit_np() requires that we currently use the
+         * address space of the task. Thus, in the remote case we just send
+         * the IPI and let schedule() handle the problem.
+         */
+
+        if (smp_processor_id() == entry->cpu) {
+                if (entry->scheduled && is_np(entry->scheduled))
+                        request_exit_np(entry->scheduled);
+                else
+                        set_tsk_need_resched(current);
+        } else
+                /* in case that it is a remote CPU we have to defer the
+                 * the decision to the remote CPU
+                 * FIXME: We could save a few IPI's here if we leave the flag
+                 * set when we are waiting for a np_exit().
+                 */
+                if (!test_will_schedule(entry->cpu))
+                        smp_send_reschedule(entry->cpu);
+}
+
+/* requeue - Put an unlinked task into gsn-edf domain.
+ *           Caller must hold gsnedf_lock.
+ */
+static noinline void requeue(struct task_struct* task)
+{
+        BUG_ON(!task);
+        /* sanity check before insertion */
+        BUG_ON(is_queued(task));
+
+        if (is_released(task, litmus_clock()))
+                __add_ready(&gsnedf, task);
+        else {
+                /* it has got to wait */
+                add_release(&gsnedf, task);
+        }
+}
+
+/* check for any necessary preemptions */
+static void check_for_preemptions(void)
+{
+        struct task_struct *task;
+        cpu_entry_t* last;
+
+        for(last = lowest_prio_cpu();
+            edf_preemption_needed(&gsnedf, last->linked);
+            last = lowest_prio_cpu()) {
+                /* preemption necessary */
+                task = __take_ready(&gsnedf);
+                TRACE("check_for_preemptions: attempting to link task %d to %d\n",
+                      task->pid, last->cpu);
+                if (last->linked)
+                        requeue(last->linked);
+                link_task_to_cpu(task, last);
+                preempt(last);
+        }
+}
+
+/* gsnedf_job_arrival: task is either resumed or released */
+static noinline void gsnedf_job_arrival(struct task_struct* task)
+{
+        BUG_ON(!task);
+
+        requeue(task);
+        check_for_preemptions();
+}
+
+static void gsnedf_release_jobs(rt_domain_t* rt, struct heap* tasks)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&gsnedf_lock, flags);
+
+        __merge_ready(rt, tasks);
+        check_for_preemptions();
+
+        spin_unlock_irqrestore(&gsnedf_lock, flags);
+}
+
+/* caller holds gsnedf_lock */
+static noinline void job_completion(struct task_struct *t, int forced)
+{
+        BUG_ON(!t);
+
+        sched_trace_task_completion(t, forced);
+
+        TRACE_TASK(t, "job_completion().\n");
+
+        /* set flags */
+        set_rt_flags(t, RT_F_SLEEP);
+        /* prepare for next period */
+        prepare_for_next_period(t);
+        if (is_released(t, litmus_clock()))
+                sched_trace_task_release(t);
+        /* unlink */
+        unlink(t);
+        /* requeue
+         * But don't requeue a blocking task. */
+        if (is_running(t))
+                gsnedf_job_arrival(t);
+}
+
+/* gsnedf_tick - this function is called for every local timer
+ *                         interrupt.
+ *
+ *                   checks whether the current task has expired and checks
+ *                   whether we need to preempt it if it has not expired
+ */
+static void gsnedf_tick(struct task_struct* t)
+{
+        if (is_realtime(t) && budget_exhausted(t)) {
+                if (!is_np(t)) {
+                        /* np tasks will be preempted when they become
+                         * preemptable again
+                         */
+                        set_tsk_need_resched(t);
+                        set_will_schedule();
+                        TRACE("gsnedf_scheduler_tick: "
+                              "%d is preemptable "
+                              " => FORCE_RESCHED\n", t->pid);
+                } else {
+                        TRACE("gsnedf_scheduler_tick: "
+                              "%d is non-preemptable, "
+                              "preemption delayed.\n", t->pid);
+                        request_exit_np(t);
+                }
+        }
+}
+
+/* Getting schedule() right is a bit tricky. schedule() may not make any
+ * assumptions on the state of the current task since it may be called for a
+ * number of reasons. The reasons include a scheduler_tick() determined that it
+ * was necessary, because sys_exit_np() was called, because some Linux
+ * subsystem determined so, or even (in the worst case) because there is a bug
+ * hidden somewhere. Thus, we must take extreme care to determine what the
+ * current state is.
+ *
+ * The CPU could currently be scheduling a task (or not), be linked (or not).
+ *
+ * The following assertions for the scheduled task could hold:
+ *
+ *      - !is_running(scheduled)        // the job blocks
+ *      - scheduled->timeslice == 0     // the job completed (forcefully)
+ *      - get_rt_flag() == RT_F_SLEEP   // the job completed (by syscall)
+ *      - linked != scheduled           // we need to reschedule (for any reason)
+ *      - is_np(scheduled)              // rescheduling must be delayed,
+ *                                         sys_exit_np must be requested
+ *
+ * Any of these can occur together.
+ */
+static struct task_struct* gsnedf_schedule(struct task_struct * prev)
+{
+        cpu_entry_t* entry = &__get_cpu_var(gsnedf_cpu_entries);
+        int out_of_time, sleep, preempt, np, exists, blocks;
+        struct task_struct* next = NULL;
+
+        spin_lock(&gsnedf_lock);
+        clear_will_schedule();
+
+        /* sanity checking */
+        BUG_ON(entry->scheduled && entry->scheduled != prev);
+        BUG_ON(entry->scheduled && !is_realtime(prev));
+        BUG_ON(is_realtime(prev) && !entry->scheduled);
+
+        /* (0) Determine state */
+        exists      = entry->scheduled != NULL;
+        blocks      = exists && !is_running(entry->scheduled);
+        out_of_time = exists && budget_exhausted(entry->scheduled);
+        np          = exists && is_np(entry->scheduled);
+        sleep       = exists && get_rt_flags(entry->scheduled) == RT_F_SLEEP;
+        preempt     = entry->scheduled != entry->linked;
+
+        TRACE_TASK(prev, "invoked gsnedf_schedule.\n");
+
+        if (exists)
+                TRACE_TASK(prev,
+                           "blocks:%d out_of_time:%d np:%d sleep:%d preempt:%d "
+                           "state:%d sig:%d\n",
+                           blocks, out_of_time, np, sleep, preempt,
+                           prev->state, signal_pending(prev));
+        if (entry->linked && preempt)
+                TRACE_TASK(prev, "will be preempted by %s/%d\n",
+                           entry->linked->comm, entry->linked->pid);
+
+
+        /* If a task blocks we have no choice but to reschedule.
+         */
+        if (blocks)
+                unlink(entry->scheduled);
+
+        /* Request a sys_exit_np() call if we would like to preempt but cannot.
+         * We need to make sure to update the link structure anyway in case
+         * that we are still linked. Multiple calls to request_exit_np() don't
+         * hurt.
+         */
+        if (np && (out_of_time || preempt || sleep)) {
+                unlink(entry->scheduled);
+                request_exit_np(entry->scheduled);
+        }
+
+        /* Any task that is preemptable and either exhausts its execution
+         * budget or wants to sleep completes. We may have to reschedule after
+         * this. Don't do a job completion if we block (can't have timers running
+         * for blocked jobs). Preemption go first for the same reason.
+         */
+        if (!np && (out_of_time || sleep) && !blocks && !preempt)
+                job_completion(entry->scheduled, !sleep);
+
+        /* Link pending task if we became unlinked.
+         */
+        if (!entry->linked)
+                link_task_to_cpu(__take_ready(&gsnedf), entry);
+
+        /* The final scheduling decision. Do we need to switch for some reason?
+         * If linked is different from scheduled, then select linked as next.
+         */
+        if ((!np || blocks) &&
+            entry->linked != entry->scheduled) {
+                /* Schedule a linked job? */
+                if (entry->linked) {
+                        entry->linked->rt_param.scheduled_on = entry->cpu;
+                        next = entry->linked;
+                }
+                if (entry->scheduled) {
+                        /* not gonna be scheduled soon */
+                        entry->scheduled->rt_param.scheduled_on = NO_CPU;
+                        TRACE_TASK(entry->scheduled, "scheduled_on = NO_CPU\n");
+                }
+        } else
+                /* Only override Linux scheduler if we have a real-time task
+                 * scheduled that needs to continue.
+                 */
+                if (exists)
+                        next = prev;
+
+        spin_unlock(&gsnedf_lock);
+
+        TRACE("gsnedf_lock released, next=0x%p\n", next);
+
+
+        if (next)
+                TRACE_TASK(next, "scheduled at %llu\n", litmus_clock());
+        else if (exists && !next)
+                TRACE("becomes idle at %llu.\n", litmus_clock());
+
+
+        return next;
+}
+
+
+/* _finish_switch - we just finished the switch away from prev
+ */
+static void gsnedf_finish_switch(struct task_struct *prev)
+{
+        cpu_entry_t*    entry = &__get_cpu_var(gsnedf_cpu_entries);
+
+        entry->scheduled = is_realtime(current) ? current : NULL;
+        TRACE_TASK(prev, "switched away from\n");
+}
+
+
+/*      Prepare a task for running in RT mode
+ */
+static void gsnedf_task_new(struct task_struct * t, int on_rq, int running)
+{
+        unsigned long           flags;
+        cpu_entry_t*            entry;
+
+        TRACE("gsn edf: task new %d\n", t->pid);
+
+        spin_lock_irqsave(&gsnedf_lock, flags);
+
+        /* setup job params */
+        release_at(t, litmus_clock());
+
+        if (running) {
+                entry = &per_cpu(gsnedf_cpu_entries, task_cpu(t));
+                BUG_ON(entry->scheduled);
+                entry->scheduled = t;
+                tsk_rt(t)->scheduled_on = task_cpu(t);
+        } else {
+                t->rt_param.scheduled_on = NO_CPU;
+        }
+        t->rt_param.linked_on          = NO_CPU;
+
+        gsnedf_job_arrival(t);
+        spin_unlock_irqrestore(&gsnedf_lock, flags);
+}
+
+static void gsnedf_task_wake_up(struct task_struct *task)
+{
+        unsigned long flags;
+        lt_t now;
+
+        TRACE_TASK(task, "wake_up at %llu\n", litmus_clock());
+
+        spin_lock_irqsave(&gsnedf_lock, flags);
+        /* 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.
+         */
+        if (get_rt_flags(task) == RT_F_EXIT_SEM) {
+                set_rt_flags(task, RT_F_RUNNING);
+        } else {
+                now = litmus_clock();
+                if (is_tardy(task, now)) {
+                        /* new sporadic release */
+                        release_at(task, now);
+                        sched_trace_task_release(task);
+                }
+                else {
+                        if (task->rt.time_slice) {
+                                /* came back in time before deadline
+                                */
+                                set_rt_flags(task, RT_F_RUNNING);
+                        }
+                }
+        }
+        gsnedf_job_arrival(task);
+        spin_unlock_irqrestore(&gsnedf_lock, flags);
+}
+
+static void gsnedf_task_block(struct task_struct *t)
+{
+        unsigned long flags;
+
+        TRACE_TASK(t, "block at %llu\n", litmus_clock());
+
+        /* unlink if necessary */
+        spin_lock_irqsave(&gsnedf_lock, flags);
+        unlink(t);
+        spin_unlock_irqrestore(&gsnedf_lock, flags);
+
+        BUG_ON(!is_realtime(t));
+}
+
+
+static void gsnedf_task_exit(struct task_struct * t)
+{
+        unsigned long flags;
+
+        /* unlink if necessary */
+        spin_lock_irqsave(&gsnedf_lock, flags);
+        unlink(t);
+        if (tsk_rt(t)->scheduled_on != NO_CPU) {
+                gsnedf_cpus[tsk_rt(t)->scheduled_on]->scheduled = NULL;
+                tsk_rt(t)->scheduled_on = NO_CPU;
+        }
+        spin_unlock_irqrestore(&gsnedf_lock, flags);
+
+        BUG_ON(!is_realtime(t));
+        TRACE_TASK(t, "RIP\n");
+}
+
+#ifdef CONFIG_FMLP
+
+/* Update the queue position of a task that got it's priority boosted via
+ * priority inheritance. */
+static void update_queue_position(struct task_struct *holder)
+{
+        /* We don't know whether holder is in the ready queue. It should, but
+         * on a budget overrun it may already be in a release queue.  Hence,
+         * calling unlink() is not possible since it assumes that the task is
+         * not in a release queue.  However, we can safely check whether
+         * sem->holder is currently in a queue or scheduled after locking both
+         * the release and the ready queue lock. */
+
+        /* Assumption: caller holds gsnedf_lock */
+
+        int check_preempt = 0;
+
+        if (tsk_rt(holder)->linked_on != NO_CPU) {
+                TRACE_TASK(holder, "%s: linked  on %d\n",
+                           __FUNCTION__, tsk_rt(holder)->linked_on);
+                /* Holder is scheduled; need to re-order CPUs.
+                 * We can't use heap_decrease() here since
+                 * the cpu_heap is ordered in reverse direction, so
+                 * it is actually an increase. */
+                heap_delete(cpu_lower_prio, &gsnedf_cpu_heap,
+                            gsnedf_cpus[tsk_rt(holder)->linked_on]->hn);
+                heap_insert(cpu_lower_prio, &gsnedf_cpu_heap,
+                            gsnedf_cpus[tsk_rt(holder)->linked_on]->hn);
+        } else {
+                /* holder may be queued: first stop queue changes */
+                spin_lock(&gsnedf.release_lock);
+                if (is_queued(holder)) {
+                        TRACE_TASK(holder, "%s: is queued\n",
+                                   __FUNCTION__);
+                        /* We need to update the position
+                         * of holder in some heap. Note that this
+                         * may be a release heap. */
+                        check_preempt =
+                                !heap_decrease(edf_ready_order,
+                                               tsk_rt(holder)->heap_node);
+                } else {
+                        /* Nothing to do: if it is not queued and not linked
+                         * then it is currently being moved by other code
+                         * (e.g., a timer interrupt handler) that will use the
+                         * correct priority when enqueuing the task. */
+                        TRACE_TASK(holder, "%s: is NOT queued => Done.\n",
+                                   __FUNCTION__);
+                }
+                spin_unlock(&gsnedf.release_lock);
+
+                /* If holder was enqueued in a release heap, then the following
+                 * preemption check is pointless, but we can't easily detect
+                 * that case. If you want to fix this, then consider that
+                 * simply adding a state flag requires O(n) time to update when
+                 * releasing n tasks, which conflicts with the goal to have
+                 * O(log n) merges. */
+                if (check_preempt) {
+                        /* heap_decrease() hit the top level of the heap: make
+                         * sure preemption checks get the right task, not the
+                         * potentially stale cache. */
+                        heap_uncache_min(edf_ready_order,
+                                         &gsnedf.ready_queue);
+                        check_for_preemptions();
+                }
+        }
+}
+
+static long gsnedf_pi_block(struct pi_semaphore *sem,
+                            struct task_struct *new_waiter)
+{
+        /* This callback has to handle the situation where a new waiter is
+         * added to the wait queue of the semaphore.
+         *
+         * We must check if has a higher priority than the currently
+         * highest-priority task, and then potentially reschedule.
+         */
+
+        BUG_ON(!new_waiter);
+
+        if (edf_higher_prio(new_waiter, sem->hp.task)) {
+                TRACE_TASK(new_waiter, " boosts priority via %p\n", sem);
+                /* called with IRQs disabled */
+                spin_lock(&gsnedf_lock);
+                /* store new highest-priority task */
+                sem->hp.task = new_waiter;
+                if (sem->holder) {
+                        TRACE_TASK(sem->holder,
+                                   " holds %p and will inherit from %s/%d\n",
+                                   sem,
+                                   new_waiter->comm, new_waiter->pid);
+                        /* let holder inherit */
+                        sem->holder->rt_param.inh_task = new_waiter;
+                        update_queue_position(sem->holder);
+                }
+                spin_unlock(&gsnedf_lock);
+        }
+
+        return 0;
+}
+
+static long gsnedf_inherit_priority(struct pi_semaphore *sem,
+                                    struct task_struct *new_owner)
+{
+        /* We don't need to acquire the gsnedf_lock since at the time of this
+         * call new_owner isn't actually scheduled yet (it's still sleeping)
+         * and since the calling function already holds sem->wait.lock, which
+         * prevents concurrent sem->hp.task changes.
+         */
+
+        if (sem->hp.task && sem->hp.task != new_owner) {
+                new_owner->rt_param.inh_task = sem->hp.task;
+                TRACE_TASK(new_owner, "inherited priority from %s/%d\n",
+                           sem->hp.task->comm, sem->hp.task->pid);
+        } else
+                TRACE_TASK(new_owner,
+                           "cannot inherit priority, "
+                           "no higher priority job waits.\n");
+        return 0;
+}
+
+/* This function is called on a semaphore release, and assumes that
+ * the current task is also the semaphore holder.
+ */
+static long gsnedf_return_priority(struct pi_semaphore *sem)
+{
+        struct task_struct* t = current;
+        int ret = 0;
+
+        /* Find new highest-priority semaphore task
+         * if holder task is the current hp.task.
+         *
+         * Calling function holds sem->wait.lock.
+         */
+        if (t == sem->hp.task)
+                edf_set_hp_task(sem);
+
+        TRACE_CUR("gsnedf_return_priority for lock %p\n", sem);
+
+        if (t->rt_param.inh_task) {
+                /* interrupts already disabled by PI code */
+                spin_lock(&gsnedf_lock);
+
+                /* Reset inh_task to NULL. */
+                t->rt_param.inh_task = NULL;
+
+                /* Check if rescheduling is necessary */
+                unlink(t);
+                gsnedf_job_arrival(t);
+                spin_unlock(&gsnedf_lock);
+        }
+
+        return ret;
+}
+
+#endif
+
+static long gsnedf_admit_task(struct task_struct* tsk)
+{
+        return 0;
+}
+
+static long gsnedf_activate_plugin(void)
+{
+        int cpu;
+        cpu_entry_t *entry;
+
+        heap_init(&gsnedf_cpu_heap);
+
+        for_each_online_cpu(cpu) {
+                entry = &per_cpu(gsnedf_cpu_entries, cpu);
+                heap_node_init(&entry->hn, entry);
+                atomic_set(&entry->will_schedule, 0);
+                entry->linked    = NULL;
+                entry->scheduled = NULL;
+                TRACE("GSN-EDF: Initializing CPU #%d.\n", cpu);
+                update_cpu_position(entry);
+        }
+        return 0;
+}
+
+/*      Plugin object   */
+static struct sched_plugin gsn_edf_plugin __cacheline_aligned_in_smp = {
+        .plugin_name            = "GSN-EDF",
+        .finish_switch          = gsnedf_finish_switch,
+        .tick                   = gsnedf_tick,
+        .task_new               = gsnedf_task_new,
+        .complete_job           = complete_job,
+        .task_exit              = gsnedf_task_exit,
+        .schedule               = gsnedf_schedule,
+        .task_wake_up           = gsnedf_task_wake_up,
+        .task_block             = gsnedf_task_block,
+#ifdef CONFIG_FMLP
+        .fmlp_active            = 1,
+        .pi_block               = gsnedf_pi_block,
+        .inherit_priority       = gsnedf_inherit_priority,
+        .return_priority        = gsnedf_return_priority,
+#endif
+        .admit_task             = gsnedf_admit_task,
+        .activate_plugin        = gsnedf_activate_plugin,
+};
+
+
+static int __init init_gsn_edf(void)
+{
+        int cpu;
+        cpu_entry_t *entry;
+
+        heap_init(&gsnedf_cpu_heap);
+        /* initialize CPU state */
+        for (cpu = 0; cpu < NR_CPUS; cpu++)  {
+                entry = &per_cpu(gsnedf_cpu_entries, cpu);
+                gsnedf_cpus[cpu] = entry;
+                atomic_set(&entry->will_schedule, 0);
+                entry->cpu       = cpu;
+                entry->hn        = &gsnedf_heap_node[cpu];
+                heap_node_init(&entry->hn, entry);
+        }
+        edf_domain_init(&gsnedf, NULL, gsnedf_release_jobs);
+        return register_sched_plugin(&gsn_edf_plugin);
+}
+
+
+module_init(init_gsn_edf);