path: root/lib/workqueue.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Quagga Work Queue Support.
 *
 * Copyright (C) 2005 Sun Microsystems, Inc.
 */

#include <zebra.h>
#include "frrevent.h"
#include "memory.h"
#include "workqueue.h"
#include "linklist.h"
#include "command.h"
#include "log.h"

DEFINE_MTYPE(LIB, WORK_QUEUE, "Work queue");
DEFINE_MTYPE_STATIC(LIB, WORK_QUEUE_ITEM, "Work queue item");
DEFINE_MTYPE_STATIC(LIB, WORK_QUEUE_NAME, "Work queue name string");

/* master list of work_queues */
static struct list _work_queues;
/* pointer primarily to avoid an otherwise harmless warning on
 * ALL_LIST_ELEMENTS_RO
 */
static struct list *work_queues = &_work_queues;

#define WORK_QUEUE_MIN_GRANULARITY 1

static struct work_queue_item *work_queue_item_new(struct work_queue *wq)
{
	struct work_queue_item *item;
	assert(wq);

	item = XCALLOC(MTYPE_WORK_QUEUE_ITEM, sizeof(struct work_queue_item));

	return item;
}

static void work_queue_item_free(struct work_queue_item *item)
{
	XFREE(MTYPE_WORK_QUEUE_ITEM, item);
	return;
}

static inline void work_queue_item_dequeue(struct work_queue *wq,
					   struct work_queue_item *item)
{
	assert(wq->item_count > 0);

	wq->item_count--;
	STAILQ_REMOVE(&wq->items, item, work_queue_item, wq);
}

static void work_queue_item_remove(struct work_queue *wq,
				   struct work_queue_item *item)
{
	assert(item && item->data);

	/* call private data deletion callback if needed */
	if (wq->spec.del_item_data)
		wq->spec.del_item_data(wq, item->data);

	work_queue_item_dequeue(wq, item);

	work_queue_item_free(item);

	return;
}

/* create new work queue */
struct work_queue *work_queue_new(struct event_loop *m, const char *queue_name)
{
	struct work_queue *new;

	new = XCALLOC(MTYPE_WORK_QUEUE, sizeof(struct work_queue));

	new->name = XSTRDUP(MTYPE_WORK_QUEUE_NAME, queue_name);
	new->master = m;
	SET_FLAG(new->flags, WQ_UNPLUGGED);

	STAILQ_INIT(&new->items);

	listnode_add(work_queues, new);

	new->cycles.granularity = WORK_QUEUE_MIN_GRANULARITY;

	/* Default values, can be overridden by caller */
	new->spec.hold = WORK_QUEUE_DEFAULT_HOLD;
	new->spec.yield = EVENT_YIELD_TIME_SLOT;
	new->spec.retry = WORK_QUEUE_DEFAULT_RETRY;

	return new;
}

void work_queue_free_and_null(struct work_queue **wqp)
{
	struct work_queue *wq = *wqp;

	EVENT_OFF(wq->thread);

	while (!work_queue_empty(wq)) {
		struct work_queue_item *item = work_queue_last_item(wq);

		work_queue_item_remove(wq, item);
	}

	listnode_delete(work_queues, wq);

	XFREE(MTYPE_WORK_QUEUE_NAME, wq->name);
	XFREE(MTYPE_WORK_QUEUE, wq);

	*wqp = NULL;
}

bool work_queue_is_scheduled(struct work_queue *wq)
{
	return event_is_scheduled(wq->thread);
}

static int work_queue_schedule(struct work_queue *wq, unsigned int delay)
{
	/* if appropriate, schedule work queue thread */
	if (CHECK_FLAG(wq->flags, WQ_UNPLUGGED) &&
	    !event_is_scheduled(wq->thread) && !work_queue_empty(wq)) {
		/* Schedule timer if there's a delay, otherwise just schedule
		 * as an 'event'
		 */
		if (delay > 0) {
			event_add_timer_msec(wq->master, work_queue_run, wq,
					     delay, &wq->thread);
			event_ignore_late_timer(wq->thread);
		} else
			event_add_event(wq->master, work_queue_run, wq, 0,
					&wq->thread);

		/* set thread yield time, if needed */
		if (event_is_scheduled(wq->thread) &&
		    wq->spec.yield != EVENT_YIELD_TIME_SLOT)
			event_set_yield_time(wq->thread, wq->spec.yield);
		return 1;
	} else
		return 0;
}

static inline void work_queue_item_enqueue(struct work_queue *wq,
					   struct work_queue_item *item)
{
	STAILQ_INSERT_TAIL(&wq->items, item, wq);
	wq->item_count++;
}

void work_queue_add(struct work_queue *wq, void *data)
{
	struct work_queue_item *item;

	assert(wq);

	item = work_queue_item_new(wq);

	item->data = data;
	work_queue_item_enqueue(wq, item);

	work_queue_schedule(wq, wq->spec.hold);

	return;
}

static void work_queue_item_requeue(struct work_queue *wq,
				    struct work_queue_item *item)
{
	work_queue_item_dequeue(wq, item);

	/* attach to end of list */
	work_queue_item_enqueue(wq, item);
}

DEFUN (show_work_queues,
       show_work_queues_cmd,
       "show work-queues",
       SHOW_STR
       "Work Queue information\n")
{
	struct listnode *node;
	struct work_queue *wq;

	vty_out(vty, "%c %8s %5s %8s %8s %21s\n", ' ', "List", "(ms) ",
		"Q. Runs", "Yields", "Cycle Counts   ");
	vty_out(vty, "%c %8s %5s %8s %8s %7s %6s %8s %6s %s\n", 'P', "Items",
		"Hold", "Total", "Total", "Best", "Gran.", "Total", "Avg.",
		"Name");

	for (ALL_LIST_ELEMENTS_RO(work_queues, node, wq)) {
		vty_out(vty, "%c %8d %5d %8ld %8ld %7d %6d %8ld %6u %s\n",
			(CHECK_FLAG(wq->flags, WQ_UNPLUGGED) ? ' ' : 'P'),
			work_queue_item_count(wq), wq->spec.hold, wq->runs,
			wq->yields, wq->cycles.best, wq->cycles.granularity,
			wq->cycles.total,
			(wq->runs) ? (unsigned int)(wq->cycles.total / wq->runs)
				   : 0,
			wq->name);
	}

	return CMD_SUCCESS;
}

void workqueue_cmd_init(void)
{
	install_element(VIEW_NODE, &show_work_queues_cmd);
}

/* 'plug' a queue: Stop it from being scheduled,
 * ie: prevent the queue from draining.
 */
void work_queue_plug(struct work_queue *wq)
{
	EVENT_OFF(wq->thread);

	UNSET_FLAG(wq->flags, WQ_UNPLUGGED);
}

/* unplug queue, schedule it again, if appropriate
 * Ie: Allow the queue to be drained again
 */
void work_queue_unplug(struct work_queue *wq)
{
	SET_FLAG(wq->flags, WQ_UNPLUGGED);

	/* if thread isnt already waiting, add one */
	work_queue_schedule(wq, wq->spec.hold);
}

/* timer thread to process a work queue
 * will reschedule itself if required,
 * otherwise work_queue_item_add
 */
void work_queue_run(struct event *thread)
{
	struct work_queue *wq;
	struct work_queue_item *item, *titem;
	wq_item_status ret = WQ_SUCCESS;
	unsigned int cycles = 0;
	char yielded = 0;

	wq = EVENT_ARG(thread);

	assert(wq);

	/* calculate cycle granularity:
	 * list iteration == 1 run
	 * listnode processing == 1 cycle
	 * granularity == # cycles between checks whether we should yield.
	 *
	 * granularity should be > 0, and can increase slowly after each run to
	 * provide some hysteris, but not past cycles.best or 2*cycles.
	 *
	 * Best: starts low, can only increase
	 *
	 * Granularity: starts at WORK_QUEUE_MIN_GRANULARITY, can be decreased
	 *              if we run to end of time slot, can increase otherwise
	 *              by a small factor.
	 *
	 * We could use just the average and save some work, however we want to
	 * be
	 * able to adjust quickly to CPU pressure. Average wont shift much if
	 * daemon has been running a long time.
	 */
	if (wq->cycles.granularity == 0)
		wq->cycles.granularity = WORK_QUEUE_MIN_GRANULARITY;

	STAILQ_FOREACH_SAFE (item, &wq->items, wq, titem) {
		assert(item->data);

		/* dont run items which are past their allowed retries */
		if (item->ran > wq->spec.max_retries) {
			work_queue_item_remove(wq, item);
			continue;
		}

		/* run and take care of items that want to be retried
		 * immediately */
		do {
			ret = wq->spec.workfunc(wq, item->data);
			item->ran++;
		} while (item->ran < wq->spec.max_retries);

		switch (ret) {
		case WQ_QUEUE_BLOCKED: {
			/* decrement item->ran again, cause this isn't an item
			 * specific error, and retry later
			 */
			item->ran--;
			goto stats;
		}
		case WQ_REQUEUE: {
			item->ran--;
			work_queue_item_requeue(wq, item);
			/* If a single node is being used with a meta-queue
			 * (e.g., zebra),
			 * update the next node as we don't want to exit the
			 * thread and
			 * reschedule it after every node. By definition,
			 * WQ_REQUEUE is
			 * meant to continue the processing; the yield logic
			 * will kick in
			 * to terminate the thread when time has exceeded.
			 */
			if (titem == NULL)
				titem = item;
			break;
		}
		case WQ_SUCCESS:
		default: {
			work_queue_item_remove(wq, item);
			break;
		}
		}

		/* completed cycle */
		cycles++;

		/* test if we should yield */
		if (!(cycles % wq->cycles.granularity) &&
		    event_should_yield(thread)) {
			yielded = 1;
			goto stats;
		}
	}

stats:

#define WQ_HYSTERESIS_FACTOR 4

	/* we yielded, check whether granularity should be reduced */
	if (yielded && (cycles < wq->cycles.granularity)) {
		wq->cycles.granularity =
			((cycles > 0) ? cycles : WORK_QUEUE_MIN_GRANULARITY);
	}
	/* otherwise, should granularity increase? */
	else if (cycles >= (wq->cycles.granularity)) {
		if (cycles > wq->cycles.best)
			wq->cycles.best = cycles;

		/* along with yielded check, provides hysteresis for granularity
		 */
		if (cycles > (wq->cycles.granularity * WQ_HYSTERESIS_FACTOR
			      * WQ_HYSTERESIS_FACTOR))
			wq->cycles.granularity *=
				WQ_HYSTERESIS_FACTOR; /* quick ramp-up */
		else if (cycles
			 > (wq->cycles.granularity * WQ_HYSTERESIS_FACTOR))
			wq->cycles.granularity += WQ_HYSTERESIS_FACTOR;
	}
#undef WQ_HYSTERIS_FACTOR

	wq->runs++;
	wq->cycles.total += cycles;
	if (yielded)
		wq->yields++;

	/* Is the queue done yet? If it is, call the completion callback. */
	if (!work_queue_empty(wq)) {
		if (ret == WQ_QUEUE_BLOCKED)
			work_queue_schedule(wq, wq->spec.retry);
		else
			work_queue_schedule(wq, 0);

	} else if (wq->spec.completion_func)
		wq->spec.completion_func(wq);
}