/* * 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 #include #include #include #include #include #include #include #include #include /* 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; /* Bail out early if we are the release master. * The release master never schedules any real-time tasks. */ if (gsnedf.release_master == entry->cpu) return 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); if (entry->cpu != gsnedf.release_master) { entry->scheduled = t; tsk_rt(t)->scheduled_on = task_cpu(t); } else { /* do not schedule on release master */ preempt(entry); /* force resched */ tsk_rt(t)->scheduled_on = NO_CPU; } } 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); gsnedf.release_master = atomic_read(&release_master_cpu); 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; if (cpu != gsnedf.release_master) { TRACE("GSN-EDF: Initializing CPU #%d.\n", cpu); update_cpu_position(entry); } else { TRACE("GSN-EDF: CPU %d is release master.\n", cpu); } } 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);