src/task.c

/*
 * Task management functions.
 *
 * Copyright 2000-2009 Willy Tarreau <w@1wt.eu>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 */

#include <string.h>

#include <import/eb32sctree.h>
#include <import/eb32tree.h>

#include <haproxy/api.h>
#include <haproxy/fd.h>
#include <haproxy/freq_ctr.h>
#include <haproxy/list.h>
#include <haproxy/pool.h>
#include <haproxy/stream.h>
#include <haproxy/task.h>
#include <haproxy/time.h>
#include <haproxy/tools.h>


DECLARE_POOL(pool_head_task,    "task",    sizeof(struct task));
DECLARE_POOL(pool_head_tasklet, "tasklet", sizeof(struct tasklet));

/* This is the memory pool containing all the signal structs. These
 * struct are used to store each required signal between two tasks.
 */
DECLARE_POOL(pool_head_notification, "notification", sizeof(struct notification));

unsigned int nb_tasks = 0;
volatile unsigned long global_tasks_mask = 0; /* Mask of threads with tasks in the global runqueue */
unsigned int tasks_run_queue = 0;
unsigned int tasks_run_queue_cur = 0;    /* copy of the run queue size */
unsigned int nb_tasks_cur = 0;     /* copy of the tasks count */
unsigned int niced_tasks = 0;      /* number of niced tasks in the run queue */

THREAD_LOCAL struct task_per_thread *sched = &task_per_thread[0]; /* scheduler context for the current thread */

__decl_aligned_spinlock(rq_lock); /* spin lock related to run queue */
__decl_aligned_rwlock(wq_lock);   /* RW lock related to the wait queue */

#ifdef USE_THREAD
struct eb_root timers;      /* sorted timers tree, global */
struct eb_root rqueue;      /* tree constituting the run queue */
int global_rqueue_size; /* Number of element sin the global runqueue */
#endif

static unsigned int rqueue_ticks;  /* insertion count */

struct task_per_thread task_per_thread[MAX_THREADS];

/* Puts the task <t> in run queue at a position depending on t->nice. <t> is
 * returned. The nice value assigns boosts in 32th of the run queue size. A
 * nice value of -1024 sets the task to -tasks_run_queue*32, while a nice value
 * of 1024 sets the task to tasks_run_queue*32. The state flags are cleared, so
 * the caller will have to set its flags after this call.
 * The task must not already be in the run queue. If unsure, use the safer
 * task_wakeup() function.
 */
void __task_wakeup(struct task *t, struct eb_root *root)
{
#ifdef USE_THREAD
	if (root == &rqueue) {
		HA_SPIN_LOCK(TASK_RQ_LOCK, &rq_lock);
	}
#endif
	/* Make sure if the task isn't in the runqueue, nobody inserts it
	 * in the meanwhile.
	 */
	_HA_ATOMIC_ADD(&tasks_run_queue, 1);
#ifdef USE_THREAD
	if (root == &rqueue) {
		global_tasks_mask |= t->thread_mask;
		__ha_barrier_store();
	}
#endif
	t->rq.key = _HA_ATOMIC_ADD(&rqueue_ticks, 1);

	if (likely(t->nice)) {
		int offset;

		_HA_ATOMIC_ADD(&niced_tasks, 1);
		offset = t->nice * (int)global.tune.runqueue_depth;
		t->rq.key += offset;
	}

	if (task_profiling_mask & tid_bit)
		t->call_date = now_mono_time();

	eb32sc_insert(root, &t->rq, t->thread_mask);
#ifdef USE_THREAD
	if (root == &rqueue) {
		global_rqueue_size++;
		_HA_ATOMIC_OR(&t->state, TASK_GLOBAL);
		HA_SPIN_UNLOCK(TASK_RQ_LOCK, &rq_lock);
	} else
#endif
	{
		int nb = ((void *)root - (void *)&task_per_thread[0].rqueue) / sizeof(task_per_thread[0]);
		task_per_thread[nb].rqueue_size++;
	}
#ifdef USE_THREAD
	/* If all threads that are supposed to handle this task are sleeping,
	 * wake one.
	 */
	if ((((t->thread_mask & all_threads_mask) & sleeping_thread_mask) ==
	     (t->thread_mask & all_threads_mask))) {
		unsigned long m = (t->thread_mask & all_threads_mask) &~ tid_bit;

		m = (m & (m - 1)) ^ m; // keep lowest bit set
		_HA_ATOMIC_AND(&sleeping_thread_mask, ~m);
		wake_thread(my_ffsl(m) - 1);
	}
#endif
	return;
}

/*
 * __task_queue()
 *
 * Inserts a task into wait queue <wq> at the position given by its expiration
 * date. It does not matter if the task was already in the wait queue or not,
 * as it will be unlinked. The task must not have an infinite expiration timer.
 * Last, tasks must not be queued further than the end of the tree, which is
 * between <now_ms> and <now_ms> + 2^31 ms (now+24days in 32bit).
 *
 * This function should not be used directly, it is meant to be called by the
 * inline version of task_queue() which performs a few cheap preliminary tests
 * before deciding to call __task_queue(). Moreover this function doesn't care
 * at all about locking so the caller must be careful when deciding whether to
 * lock or not around this call.
 */
void __task_queue(struct task *task, struct eb_root *wq)
{
	if (likely(task_in_wq(task)))
		__task_unlink_wq(task);

	/* the task is not in the queue now */
	task->wq.key = task->expire;
#ifdef DEBUG_CHECK_INVALID_EXPIRATION_DATES
	if (tick_is_lt(task->wq.key, now_ms))
		/* we're queuing too far away or in the past (most likely) */
		return;
#endif

	eb32_insert(wq, &task->wq);
}

/*
 * Extract all expired timers from the timer queue, and wakes up all
 * associated tasks.
 */
void wake_expired_tasks()
{
	struct task_per_thread * const tt = sched; // thread's tasks
	struct task *task;
	struct eb32_node *eb;
	__decl_thread(int key);

	while (1) {
  lookup_next_local:
		eb = eb32_lookup_ge(&tt->timers, now_ms - TIMER_LOOK_BACK);
		if (!eb) {
			/* we might have reached the end of the tree, typically because
			* <now_ms> is in the first half and we're first scanning the last
			* half. Let's loop back to the beginning of the tree now.
			*/
			eb = eb32_first(&tt->timers);
			if (likely(!eb))
				break;
		}

		/* It is possible that this task was left at an earlier place in the
		 * tree because a recent call to task_queue() has not moved it. This
		 * happens when the new expiration date is later than the old one.
		 * Since it is very unlikely that we reach a timeout anyway, it's a
		 * lot cheaper to proceed like this because we almost never update
		 * the tree. We may also find disabled expiration dates there. Since
		 * we have detached the task from the tree, we simply call task_queue
		 * to take care of this. Note that we might occasionally requeue it at
		 * the same place, before <eb>, so we have to check if this happens,
		 * and adjust <eb>, otherwise we may skip it which is not what we want.
		 * We may also not requeue the task (and not point eb at it) if its
		 * expiration time is not set. We also make sure we leave the real
		 * expiration date for the next task in the queue so that when calling
		 * next_timer_expiry() we're guaranteed to see the next real date and
		 * not the next apparent date. This is in order to avoid useless
		 * wakeups.
		 */

		task = eb32_entry(eb, struct task, wq);
		if (tick_is_expired(task->expire, now_ms)) {
			/* expired task, wake it up */
			__task_unlink_wq(task);
			task_wakeup(task, TASK_WOKEN_TIMER);
		}
		else if (task->expire != eb->key) {
			/* task is not expired but its key doesn't match so let's
			 * update it and skip to next apparently expired task.
			 */
			__task_unlink_wq(task);
			if (tick_isset(task->expire))
				__task_queue(task, &tt->timers);
		}
		else {
			/* task not expired and correctly placed */
			break;
		}
	}

#ifdef USE_THREAD
	if (eb_is_empty(&timers))
		goto leave;

	HA_RWLOCK_RDLOCK(TASK_WQ_LOCK, &wq_lock);
	eb = eb32_lookup_ge(&timers, now_ms - TIMER_LOOK_BACK);
	if (!eb) {
		eb = eb32_first(&timers);
		if (likely(!eb)) {
			HA_RWLOCK_RDUNLOCK(TASK_WQ_LOCK, &wq_lock);
			goto leave;
		}
	}
	key = eb->key;
	HA_RWLOCK_RDUNLOCK(TASK_WQ_LOCK, &wq_lock);

	if (tick_is_lt(now_ms, key))
		goto leave;

	/* There's really something of interest here, let's visit the queue */

	while (1) {
		HA_RWLOCK_WRLOCK(TASK_WQ_LOCK, &wq_lock);
  lookup_next:
		eb = eb32_lookup_ge(&timers, now_ms - TIMER_LOOK_BACK);
		if (!eb) {
			/* we might have reached the end of the tree, typically because
			* <now_ms> is in the first half and we're first scanning the last
			* half. Let's loop back to the beginning of the tree now.
			*/
			eb = eb32_first(&timers);
			if (likely(!eb))
				break;
		}

		task = eb32_entry(eb, struct task, wq);
		if (tick_is_expired(task->expire, now_ms)) {
			/* expired task, wake it up */
			__task_unlink_wq(task);
			task_wakeup(task, TASK_WOKEN_TIMER);
		}
		else if (task->expire != eb->key) {
			/* task is not expired but its key doesn't match so let's
			 * update it and skip to next apparently expired task.
			 */
			__task_unlink_wq(task);
			if (tick_isset(task->expire))
				__task_queue(task, &tt->timers);
			goto lookup_next;
		}
		else {
			/* task not expired and correctly placed */
			break;
		}
		HA_RWLOCK_WRUNLOCK(TASK_WQ_LOCK, &wq_lock);
	}

	HA_RWLOCK_WRUNLOCK(TASK_WQ_LOCK, &wq_lock);
#endif
leave:
	return;
}

/* Checks the next timer for the current thread by looking into its own timer
 * list and the global one. It may return TICK_ETERNITY if no timer is present.
 * Note that the next timer might very well be slightly in the past.
 */
int next_timer_expiry()
{
	struct task_per_thread * const tt = sched; // thread's tasks
	struct eb32_node *eb;
	int ret = TICK_ETERNITY;
	__decl_thread(int key);

	/* first check in the thread-local timers */
	eb = eb32_lookup_ge(&tt->timers, now_ms - TIMER_LOOK_BACK);
	if (!eb) {
		/* we might have reached the end of the tree, typically because
		 * <now_ms> is in the first half and we're first scanning the last
		 * half. Let's loop back to the beginning of the tree now.
		 */
		eb = eb32_first(&tt->timers);
	}

	if (eb)
		ret = eb->key;

#ifdef USE_THREAD
	if (!eb_is_empty(&timers)) {
		HA_RWLOCK_RDLOCK(TASK_WQ_LOCK, &wq_lock);
		eb = eb32_lookup_ge(&timers, now_ms - TIMER_LOOK_BACK);
		if (!eb)
			eb = eb32_first(&timers);
		if (eb)
			key = eb->key;
		HA_RWLOCK_RDUNLOCK(TASK_WQ_LOCK, &wq_lock);
		if (eb)
			ret = tick_first(ret, key);
	}
#endif
	return ret;
}

/* Walks over tasklet list <list> and run at most <max> of them. Returns
 * the number of entries effectively processed (tasks and tasklets merged).
 * The count of tasks in the list for the current thread is adjusted.
 */
int run_tasks_from_list(struct list *list, int max)
{
	struct task *(*process)(struct task *t, void *ctx, unsigned short state);
	struct task *t;
	unsigned short state;
	void *ctx;
	int done = 0;

	while (done < max && !LIST_ISEMPTY(list)) {
		t = (struct task *)LIST_ELEM(list->n, struct tasklet *, list);
		state = (t->state & (TASK_SHARED_WQ|TASK_SELF_WAKING));

		ti->flags &= ~TI_FL_STUCK; // this thread is still running
		activity[tid].ctxsw++;
		ctx = t->context;
		process = t->process;
		t->calls++;
		sched->current = t;

		if (TASK_IS_TASKLET(t)) {
			state = _HA_ATOMIC_XCHG(&t->state, state);
			__ha_barrier_atomic_store();
			__tasklet_remove_from_tasklet_list((struct tasklet *)t);
			process(t, ctx, state);
			done++;
			sched->current = NULL;
			__ha_barrier_store();
			continue;
		}

		state = _HA_ATOMIC_XCHG(&t->state, state | TASK_RUNNING);
		__ha_barrier_atomic_store();
		__tasklet_remove_from_tasklet_list((struct tasklet *)t);

		/* OK then this is a regular task */

		task_per_thread[tid].task_list_size--;
		if (unlikely(t->call_date)) {
			uint64_t now_ns = now_mono_time();

			t->lat_time += now_ns - t->call_date;
			t->call_date = now_ns;
		}

		__ha_barrier_store();
		if (likely(process == process_stream))
			t = process_stream(t, ctx, state);
		else if (process != NULL)
			t = process(t, ctx, state);
		else {
			__task_free(t);
			sched->current = NULL;
			__ha_barrier_store();
			/* We don't want max_processed to be decremented if
			 * we're just freeing a destroyed task, we should only
			 * do so if we really ran a task.
			 */
			continue;
		}
		sched->current = NULL;
		__ha_barrier_store();
		/* If there is a pending state  we have to wake up the task
		 * immediately, else we defer it into wait queue
		 */
		if (t != NULL) {
			if (unlikely(t->call_date)) {
				t->cpu_time += now_mono_time() - t->call_date;
				t->call_date = 0;
			}

			state = _HA_ATOMIC_AND(&t->state, ~TASK_RUNNING);
			if (state & TASK_WOKEN_ANY)
				task_wakeup(t, 0);
			else
				task_queue(t);
		}
		done++;
	}

	return done;
}

/* The run queue is chronologically sorted in a tree. An insertion counter is
 * used to assign a position to each task. This counter may be combined with
 * other variables (eg: nice value) to set the final position in the tree. The
 * counter may wrap without a problem, of course. We then limit the number of
 * tasks processed to 200 in any case, so that general latency remains low and
 * so that task positions have a chance to be considered. The function scans
 * both the global and local run queues and picks the most urgent task between
 * the two. We need to grab the global runqueue lock to touch it so it's taken
 * on the very first access to the global run queue and is released as soon as
 * it reaches the end.
 *
 * The function adjusts <next> if a new event is closer.
 */
void process_runnable_tasks()
{
	struct task_per_thread * const tt = sched;
	struct eb32sc_node *lrq; // next local run queue entry
	struct eb32sc_node *grq; // next global run queue entry
	struct task *t;
	const unsigned int default_weights[TL_CLASSES] = {
		[TL_URGENT] = 64, // ~50% of CPU bandwidth for I/O
		[TL_NORMAL] = 48, // ~37% of CPU bandwidth for tasks
		[TL_BULK]   = 16, // ~13% of CPU bandwidth for self-wakers
	};
	unsigned int max[TL_CLASSES]; // max to be run per class
	unsigned int max_total;       // sum of max above
	struct mt_list *tmp_list;
	unsigned int queue;
	int max_processed;

	ti->flags &= ~TI_FL_STUCK; // this thread is still running

	if (!thread_has_tasks()) {
		activity[tid].empty_rq++;
		return;
	}

	tasks_run_queue_cur = tasks_run_queue; /* keep a copy for reporting */
	nb_tasks_cur = nb_tasks;
	max_processed = global.tune.runqueue_depth;

	if (likely(niced_tasks))
		max_processed = (max_processed + 3) / 4;

 not_done_yet:
	max[TL_URGENT] = max[TL_NORMAL] = max[TL_BULK] = 0;

	/* urgent tasklets list gets a default weight of ~50% */
	if ((tt->tl_class_mask & (1 << TL_URGENT)) ||
	    !MT_LIST_ISEMPTY(&tt->shared_tasklet_list))
		max[TL_URGENT] = default_weights[TL_URGENT];

	/* normal tasklets list gets a default weight of ~37% */
	if ((tt->tl_class_mask & (1 << TL_NORMAL)) ||
	    (sched->rqueue_size > 0) || (global_tasks_mask & tid_bit))
		max[TL_NORMAL] = default_weights[TL_NORMAL];

	/* bulk tasklets list gets a default weight of ~13% */
	if ((tt->tl_class_mask & (1 << TL_BULK)))
		max[TL_BULK] = default_weights[TL_BULK];

	/* Now compute a fair share of the weights. Total may slightly exceed
	 * 100% due to rounding, this is not a problem. Note that by design
	 * the sum cannot be NULL as we cannot get there without tasklets to
	 * process.
	 */
	max_total = max[TL_URGENT] + max[TL_NORMAL] + max[TL_BULK];
	for (queue = 0; queue < TL_CLASSES; queue++)
		max[queue]  = ((unsigned)max_processed * max[queue] + max_total - 1) / max_total;

	lrq = grq = NULL;

	/* pick up to max[TL_NORMAL] regular tasks from prio-ordered run queues */
	/* Note: the grq lock is always held when grq is not null */
	while (tt->task_list_size < max[TL_NORMAL]) {
		if ((global_tasks_mask & tid_bit) && !grq) {
#ifdef USE_THREAD
			HA_SPIN_LOCK(TASK_RQ_LOCK, &rq_lock);
			grq = eb32sc_lookup_ge(&rqueue, rqueue_ticks - TIMER_LOOK_BACK, tid_bit);
			if (unlikely(!grq)) {
				grq = eb32sc_first(&rqueue, tid_bit);
				if (!grq) {
					global_tasks_mask &= ~tid_bit;
					HA_SPIN_UNLOCK(TASK_RQ_LOCK, &rq_lock);
				}
			}
#endif
		}

		/* If a global task is available for this thread, it's in grq
		 * now and the global RQ is locked.
		 */

		if (!lrq) {
			lrq = eb32sc_lookup_ge(&tt->rqueue, rqueue_ticks - TIMER_LOOK_BACK, tid_bit);
			if (unlikely(!lrq))
				lrq = eb32sc_first(&tt->rqueue, tid_bit);
		}

		if (!lrq && !grq)
			break;

		if (likely(!grq || (lrq && (int)(lrq->key - grq->key) <= 0))) {
			t = eb32sc_entry(lrq, struct task, rq);
			lrq = eb32sc_next(lrq, tid_bit);
			__task_unlink_rq(t);
		}
#ifdef USE_THREAD
		else {
			t = eb32sc_entry(grq, struct task, rq);
			grq = eb32sc_next(grq, tid_bit);
			__task_unlink_rq(t);
			if (unlikely(!grq)) {
				grq = eb32sc_first(&rqueue, tid_bit);
				if (!grq) {
					global_tasks_mask &= ~tid_bit;
					HA_SPIN_UNLOCK(TASK_RQ_LOCK, &rq_lock);
				}
			}
		}
#endif

		/* Make sure the entry doesn't appear to be in a list */
		LIST_INIT(&((struct tasklet *)t)->list);
		/* And add it to the local task list */
		tasklet_insert_into_tasklet_list(&tt->tasklets[TL_NORMAL], (struct tasklet *)t);
		tt->tl_class_mask |= 1 << TL_NORMAL;
		tt->task_list_size++;
		activity[tid].tasksw++;
	}

	/* release the rqueue lock */
	if (grq) {
		HA_SPIN_UNLOCK(TASK_RQ_LOCK, &rq_lock);
		grq = NULL;
	}

	/* Merge the list of tasklets waken up by other threads to the
	 * main list.
	 */
	tmp_list = MT_LIST_BEHEAD(&tt->shared_tasklet_list);
	if (tmp_list) {
		LIST_SPLICE_END_DETACHED(&tt->tasklets[TL_URGENT], (struct list *)tmp_list);
		if (!LIST_ISEMPTY(&tt->tasklets[TL_URGENT]))
			tt->tl_class_mask |= 1 << TL_URGENT;
	}

	/* execute tasklets in each queue */
	for (queue = 0; queue < TL_CLASSES; queue++) {
		if (max[queue] > 0) {
			tt->current_queue = queue;
			max_processed -= run_tasks_from_list(&tt->tasklets[queue], max[queue]);
			tt->current_queue = -1;
			if (LIST_ISEMPTY(&tt->tasklets[queue]))
				tt->tl_class_mask &= ~(1 << queue);
		}
	}

	/* some tasks may have woken other ones up */
	if (max_processed > 0 && thread_has_tasks())
		goto not_done_yet;

	if (tt->tl_class_mask)
		activity[tid].long_rq++;
}

/* create a work list array for <nbthread> threads, using tasks made of
 * function <fct>. The context passed to the function will be the pointer to
 * the thread's work list, which will contain a copy of argument <arg>. The
 * wake up reason will be TASK_WOKEN_OTHER. The pointer to the work_list array
 * is returned on success, otherwise NULL on failure.
 */
struct work_list *work_list_create(int nbthread,
                                   struct task *(*fct)(struct task *, void *, unsigned short),
                                   void *arg)
{
	struct work_list *wl;
	int i;

	wl = calloc(nbthread, sizeof(*wl));
	if (!wl)
		goto fail;

	for (i = 0; i < nbthread; i++) {
		MT_LIST_INIT(&wl[i].head);
		wl[i].task = task_new(1UL << i);
		if (!wl[i].task)
			goto fail;
		wl[i].task->process = fct;
		wl[i].task->context = &wl[i];
		wl[i].arg = arg;
	}
	return wl;

 fail:
	work_list_destroy(wl, nbthread);
	return NULL;
}

/* destroy work list <work> */
void work_list_destroy(struct work_list *work, int nbthread)
{
	int t;

	if (!work)
		return;
	for (t = 0; t < nbthread; t++)
		task_destroy(work[t].task);
	free(work);
}

/*
 * Delete every tasks before running the master polling loop
 */
void mworker_cleantasks()
{
	struct task *t;
	int i;
	struct eb32_node *tmp_wq = NULL;
	struct eb32sc_node *tmp_rq = NULL;

#ifdef USE_THREAD
	/* cleanup the global run queue */
	tmp_rq = eb32sc_first(&rqueue, MAX_THREADS_MASK);
	while (tmp_rq) {
		t = eb32sc_entry(tmp_rq, struct task, rq);
		tmp_rq = eb32sc_next(tmp_rq, MAX_THREADS_MASK);
		task_destroy(t);
	}
	/* cleanup the timers queue */
	tmp_wq = eb32_first(&timers);
	while (tmp_wq) {
		t = eb32_entry(tmp_wq, struct task, wq);
		tmp_wq = eb32_next(tmp_wq);
		task_destroy(t);
	}
#endif
	/* clean the per thread run queue */
	for (i = 0; i < global.nbthread; i++) {
		tmp_rq = eb32sc_first(&task_per_thread[i].rqueue, MAX_THREADS_MASK);
		while (tmp_rq) {
			t = eb32sc_entry(tmp_rq, struct task, rq);
			tmp_rq = eb32sc_next(tmp_rq, MAX_THREADS_MASK);
			task_destroy(t);
		}
		/* cleanup the per thread timers queue */
		tmp_wq = eb32_first(&task_per_thread[i].timers);
		while (tmp_wq) {
			t = eb32_entry(tmp_wq, struct task, wq);
			tmp_wq = eb32_next(tmp_wq);
			task_destroy(t);
		}
	}
}

/* perform minimal intializations */
static void init_task()
{
	int i;

#ifdef USE_THREAD
	memset(&timers, 0, sizeof(timers));
	memset(&rqueue, 0, sizeof(rqueue));
#endif
	memset(&task_per_thread, 0, sizeof(task_per_thread));
	for (i = 0; i < MAX_THREADS; i++) {
		LIST_INIT(&task_per_thread[i].tasklets[TL_URGENT]);
		LIST_INIT(&task_per_thread[i].tasklets[TL_NORMAL]);
		LIST_INIT(&task_per_thread[i].tasklets[TL_BULK]);
		MT_LIST_INIT(&task_per_thread[i].shared_tasklet_list);
	}
}

INITCALL0(STG_PREPARE, init_task);

/*
 * Local variables:
 *  c-indent-level: 8
 *  c-basic-offset: 8
 * End:
 */