2 * Copyright (C) 2007 Oracle. All rights reserved.
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public
6 * License v2 as published by the Free Software Foundation.
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public
14 * License along with this program; if not, write to the
15 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
16 * Boston, MA 021110-1307, USA.
19 #include <linux/kthread.h>
20 #include <linux/list.h>
21 #include <linux/spinlock.h>
22 #include <linux/freezer.h>
23 #include "async-thread.h"
25 #define WORK_QUEUED_BIT 0
26 #define WORK_DONE_BIT 1
27 #define WORK_ORDER_DONE_BIT 2
28 #define WORK_HIGH_PRIO_BIT 3
31 * container for the kthread task pointer and the list of pending work
32 * One of these is allocated per thread.
34 struct btrfs_worker_thread {
35 /* pool we belong to */
36 struct btrfs_workers *workers;
38 /* list of struct btrfs_work that are waiting for service */
39 struct list_head pending;
40 struct list_head prio_pending;
42 /* list of worker threads from struct btrfs_workers */
43 struct list_head worker_list;
46 struct task_struct *task;
48 /* number of things on the pending list */
51 unsigned long sequence;
53 /* protects the pending list. */
56 /* set to non-zero when this thread is already awake and kicking */
59 /* are we currently idle */
64 * helper function to move a thread onto the idle list after it
65 * has finished some requests.
67 static void check_idle_worker(struct btrfs_worker_thread *worker)
69 if (!worker->idle && atomic_read(&worker->num_pending) <
70 worker->workers->idle_thresh / 2) {
72 spin_lock_irqsave(&worker->workers->lock, flags);
74 list_move(&worker->worker_list, &worker->workers->idle_list);
75 spin_unlock_irqrestore(&worker->workers->lock, flags);
80 * helper function to move a thread off the idle list after new
81 * pending work is added.
83 static void check_busy_worker(struct btrfs_worker_thread *worker)
85 if (worker->idle && atomic_read(&worker->num_pending) >=
86 worker->workers->idle_thresh) {
88 spin_lock_irqsave(&worker->workers->lock, flags);
90 list_move_tail(&worker->worker_list,
91 &worker->workers->worker_list);
92 spin_unlock_irqrestore(&worker->workers->lock, flags);
96 static noinline int run_ordered_completions(struct btrfs_workers *workers,
97 struct btrfs_work *work)
101 if (!workers->ordered)
104 set_bit(WORK_DONE_BIT, &work->flags);
106 spin_lock_irqsave(&workers->lock, flags);
109 if (!list_empty(&workers->prio_order_list)) {
110 work = list_entry(workers->prio_order_list.next,
111 struct btrfs_work, order_list);
112 } else if (!list_empty(&workers->order_list)) {
113 work = list_entry(workers->order_list.next,
114 struct btrfs_work, order_list);
118 if (!test_bit(WORK_DONE_BIT, &work->flags))
121 /* we are going to call the ordered done function, but
122 * we leave the work item on the list as a barrier so
123 * that later work items that are done don't have their
124 * functions called before this one returns
126 if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
129 spin_unlock_irqrestore(&workers->lock, flags);
131 work->ordered_func(work);
133 /* now take the lock again and call the freeing code */
134 spin_lock_irqsave(&workers->lock, flags);
135 list_del(&work->order_list);
136 work->ordered_free(work);
139 spin_unlock_irqrestore(&workers->lock, flags);
144 * main loop for servicing work items
146 static int worker_loop(void *arg)
148 struct btrfs_worker_thread *worker = arg;
149 struct list_head *cur;
150 struct btrfs_work *work;
152 spin_lock_irq(&worker->lock);
155 if (!list_empty(&worker->prio_pending))
156 cur = worker->prio_pending.next;
157 else if (!list_empty(&worker->pending))
158 cur = worker->pending.next;
162 work = list_entry(cur, struct btrfs_work, list);
163 list_del(&work->list);
164 clear_bit(WORK_QUEUED_BIT, &work->flags);
166 work->worker = worker;
167 spin_unlock_irq(&worker->lock);
171 atomic_dec(&worker->num_pending);
173 * unless this is an ordered work queue,
174 * 'work' was probably freed by func above.
176 run_ordered_completions(worker->workers, work);
178 spin_lock_irq(&worker->lock);
179 check_idle_worker(worker);
181 if (freezing(current)) {
183 spin_unlock_irq(&worker->lock);
186 spin_unlock_irq(&worker->lock);
187 if (!kthread_should_stop()) {
190 * we've dropped the lock, did someone else
194 if (!list_empty(&worker->pending) ||
195 !list_empty(&worker->prio_pending))
199 * this short schedule allows more work to
200 * come in without the queue functions
201 * needing to go through wake_up_process()
203 * worker->working is still 1, so nobody
204 * is going to try and wake us up
208 if (!list_empty(&worker->pending) ||
209 !list_empty(&worker->prio_pending))
212 if (kthread_should_stop())
215 /* still no more work?, sleep for real */
216 spin_lock_irq(&worker->lock);
217 set_current_state(TASK_INTERRUPTIBLE);
218 if (!list_empty(&worker->pending) ||
219 !list_empty(&worker->prio_pending))
223 * this makes sure we get a wakeup when someone
224 * adds something new to the queue
227 spin_unlock_irq(&worker->lock);
229 if (!kthread_should_stop())
232 __set_current_state(TASK_RUNNING);
234 } while (!kthread_should_stop());
239 * this will wait for all the worker threads to shutdown
241 int btrfs_stop_workers(struct btrfs_workers *workers)
243 struct list_head *cur;
244 struct btrfs_worker_thread *worker;
246 list_splice_init(&workers->idle_list, &workers->worker_list);
247 while (!list_empty(&workers->worker_list)) {
248 cur = workers->worker_list.next;
249 worker = list_entry(cur, struct btrfs_worker_thread,
251 kthread_stop(worker->task);
252 list_del(&worker->worker_list);
259 * simple init on struct btrfs_workers
261 void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max)
263 workers->num_workers = 0;
264 INIT_LIST_HEAD(&workers->worker_list);
265 INIT_LIST_HEAD(&workers->idle_list);
266 INIT_LIST_HEAD(&workers->order_list);
267 INIT_LIST_HEAD(&workers->prio_order_list);
268 spin_lock_init(&workers->lock);
269 workers->max_workers = max;
270 workers->idle_thresh = 32;
271 workers->name = name;
272 workers->ordered = 0;
276 * starts new worker threads. This does not enforce the max worker
277 * count in case you need to temporarily go past it.
279 int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
281 struct btrfs_worker_thread *worker;
285 for (i = 0; i < num_workers; i++) {
286 worker = kzalloc(sizeof(*worker), GFP_NOFS);
292 INIT_LIST_HEAD(&worker->pending);
293 INIT_LIST_HEAD(&worker->prio_pending);
294 INIT_LIST_HEAD(&worker->worker_list);
295 spin_lock_init(&worker->lock);
296 atomic_set(&worker->num_pending, 0);
297 worker->workers = workers;
298 worker->task = kthread_run(worker_loop, worker,
299 "btrfs-%s-%d", workers->name,
300 workers->num_workers + i);
301 if (IS_ERR(worker->task)) {
303 ret = PTR_ERR(worker->task);
307 spin_lock_irq(&workers->lock);
308 list_add_tail(&worker->worker_list, &workers->idle_list);
310 workers->num_workers++;
311 spin_unlock_irq(&workers->lock);
315 btrfs_stop_workers(workers);
320 * run through the list and find a worker thread that doesn't have a lot
321 * to do right now. This can return null if we aren't yet at the thread
322 * count limit and all of the threads are busy.
324 static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
326 struct btrfs_worker_thread *worker;
327 struct list_head *next;
328 int enforce_min = workers->num_workers < workers->max_workers;
331 * if we find an idle thread, don't move it to the end of the
332 * idle list. This improves the chance that the next submission
333 * will reuse the same thread, and maybe catch it while it is still
336 if (!list_empty(&workers->idle_list)) {
337 next = workers->idle_list.next;
338 worker = list_entry(next, struct btrfs_worker_thread,
342 if (enforce_min || list_empty(&workers->worker_list))
346 * if we pick a busy task, move the task to the end of the list.
347 * hopefully this will keep things somewhat evenly balanced.
348 * Do the move in batches based on the sequence number. This groups
349 * requests submitted at roughly the same time onto the same worker.
351 next = workers->worker_list.next;
352 worker = list_entry(next, struct btrfs_worker_thread, worker_list);
353 atomic_inc(&worker->num_pending);
356 if (worker->sequence % workers->idle_thresh == 0)
357 list_move_tail(next, &workers->worker_list);
362 * selects a worker thread to take the next job. This will either find
363 * an idle worker, start a new worker up to the max count, or just return
364 * one of the existing busy workers.
366 static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
368 struct btrfs_worker_thread *worker;
372 spin_lock_irqsave(&workers->lock, flags);
373 worker = next_worker(workers);
374 spin_unlock_irqrestore(&workers->lock, flags);
377 spin_lock_irqsave(&workers->lock, flags);
378 if (workers->num_workers >= workers->max_workers) {
379 struct list_head *fallback = NULL;
381 * we have failed to find any workers, just
382 * return the force one
384 if (!list_empty(&workers->worker_list))
385 fallback = workers->worker_list.next;
386 if (!list_empty(&workers->idle_list))
387 fallback = workers->idle_list.next;
389 worker = list_entry(fallback,
390 struct btrfs_worker_thread, worker_list);
391 spin_unlock_irqrestore(&workers->lock, flags);
393 spin_unlock_irqrestore(&workers->lock, flags);
394 /* we're below the limit, start another worker */
395 btrfs_start_workers(workers, 1);
403 * btrfs_requeue_work just puts the work item back on the tail of the list
404 * it was taken from. It is intended for use with long running work functions
405 * that make some progress and want to give the cpu up for others.
407 int btrfs_requeue_work(struct btrfs_work *work)
409 struct btrfs_worker_thread *worker = work->worker;
413 if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
416 spin_lock_irqsave(&worker->lock, flags);
417 if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
418 list_add_tail(&work->list, &worker->prio_pending);
420 list_add_tail(&work->list, &worker->pending);
421 atomic_inc(&worker->num_pending);
423 /* by definition we're busy, take ourselves off the idle
427 spin_lock_irqsave(&worker->workers->lock, flags);
429 list_move_tail(&worker->worker_list,
430 &worker->workers->worker_list);
431 spin_unlock_irqrestore(&worker->workers->lock, flags);
433 if (!worker->working) {
438 spin_unlock_irqrestore(&worker->lock, flags);
440 wake_up_process(worker->task);
446 void btrfs_set_work_high_prio(struct btrfs_work *work)
448 set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
452 * places a struct btrfs_work into the pending queue of one of the kthreads
454 int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
456 struct btrfs_worker_thread *worker;
460 /* don't requeue something already on a list */
461 if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
464 worker = find_worker(workers);
465 if (workers->ordered) {
466 spin_lock_irqsave(&workers->lock, flags);
467 if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
468 list_add_tail(&work->order_list,
469 &workers->prio_order_list);
471 list_add_tail(&work->order_list, &workers->order_list);
473 spin_unlock_irqrestore(&workers->lock, flags);
475 INIT_LIST_HEAD(&work->order_list);
478 spin_lock_irqsave(&worker->lock, flags);
480 if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
481 list_add_tail(&work->list, &worker->prio_pending);
483 list_add_tail(&work->list, &worker->pending);
484 atomic_inc(&worker->num_pending);
485 check_busy_worker(worker);
488 * avoid calling into wake_up_process if this thread has already
491 if (!worker->working)
495 spin_unlock_irqrestore(&worker->lock, flags);
498 wake_up_process(worker->task);