1/*
  2 *  Deadline i/o scheduler.
  3 *
  4 *  Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
  5 */
  6#include <linux/kernel.h>
  7#include <linux/fs.h>
  8#include <linux/blkdev.h>
  9#include <linux/elevator.h>
 10#include <linux/bio.h>
 11#include <linux/module.h>
 12#include <linux/slab.h>
 13#include <linux/init.h>
 14#include <linux/compiler.h>
 15#include <linux/rbtree.h>
 16
 17/*
 18 * See Documentation/block/deadline-iosched.txt
 19 */
 20static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
 21static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
 22static const int writes_starved = 2;    /* max times reads can starve a write */
 23static const int fifo_batch = 16;       /* # of sequential requests treated as one
 24				     by the above parameters. For throughput. */
 25
 26struct deadline_data {
 27	/*
 28	 * run time data
 29	 */
 30
 31	/*
 32	 * requests (deadline_rq s) are present on both sort_list and fifo_list
 33	 */
 34	struct rb_root sort_list[2];	
 35	struct list_head fifo_list[2];
 36
 37	/*
 38	 * next in sort order. read, write or both are NULL
 39	 */
 40	struct request *next_rq[2];
 41	unsigned int batching;		/* number of sequential requests made */
 42	unsigned int starved;		/* times reads have starved writes */
 43
 44	/*
 45	 * settings that change how the i/o scheduler behaves
 46	 */
 47	int fifo_expire[2];
 48	int fifo_batch;
 49	int writes_starved;
 50	int front_merges;
 51};
 52
 53static inline struct rb_root *
 54deadline_rb_root(struct deadline_data *dd, struct request *rq)
 55{
 56	return &dd->sort_list[rq_data_dir(rq)];
 57}
 58
 59/*
 60 * get the request after `rq' in sector-sorted order
 61 */
 62static inline struct request *
 63deadline_latter_request(struct request *rq)
 64{
 65	struct rb_node *node = rb_next(&rq->rb_node);
 66
 67	if (node)
 68		return rb_entry_rq(node);
 69
 70	return NULL;
 71}
 72
 73static void
 74deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
 75{
 76	struct rb_root *root = deadline_rb_root(dd, rq);
 77
 78	elv_rb_add(root, rq);
 79}
 80
 81static inline void
 82deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
 83{
 84	const int data_dir = rq_data_dir(rq);
 85
 86	if (dd->next_rq[data_dir] == rq)
 87		dd->next_rq[data_dir] = deadline_latter_request(rq);
 88
 89	elv_rb_del(deadline_rb_root(dd, rq), rq);
 90}
 91
 92/*
 93 * add rq to rbtree and fifo
 94 */
 95static void
 96deadline_add_request(struct request_queue *q, struct request *rq)
 97{
 98	struct deadline_data *dd = q->elevator->elevator_data;
 99	const int data_dir = rq_data_dir(rq);
100
101	/*
102	 * This may be a requeue of a write request that has locked its
103	 * target zone. If it is the case, this releases the zone lock.
104	 */
105	blk_req_zone_write_unlock(rq);
106
107	deadline_add_rq_rb(dd, rq);
108
109	/*
110	 * set expire time and add to fifo list
111	 */
112	rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
113	list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
114}
115
116/*
117 * remove rq from rbtree and fifo.
118 */
119static void deadline_remove_request(struct request_queue *q, struct request *rq)
120{
121	struct deadline_data *dd = q->elevator->elevator_data;
122
123	rq_fifo_clear(rq);
124	deadline_del_rq_rb(dd, rq);
125}
126
127static enum elv_merge
128deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
129{
130	struct deadline_data *dd = q->elevator->elevator_data;
131	struct request *__rq;
132
133	/*
134	 * check for front merge
135	 */
136	if (dd->front_merges) {
137		sector_t sector = bio_end_sector(bio);
138
139		__rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
140		if (__rq) {
141			BUG_ON(sector != blk_rq_pos(__rq));
142
143			if (elv_bio_merge_ok(__rq, bio)) {
144				*req = __rq;
145				return ELEVATOR_FRONT_MERGE;
146			}
147		}
148	}
149
150	return ELEVATOR_NO_MERGE;
151}
152
153static void deadline_merged_request(struct request_queue *q,
154				    struct request *req, enum elv_merge type)
155{
156	struct deadline_data *dd = q->elevator->elevator_data;
157
158	/*
159	 * if the merge was a front merge, we need to reposition request
160	 */
161	if (type == ELEVATOR_FRONT_MERGE) {
162		elv_rb_del(deadline_rb_root(dd, req), req);
163		deadline_add_rq_rb(dd, req);
164	}
165}
166
167static void
168deadline_merged_requests(struct request_queue *q, struct request *req,
169			 struct request *next)
170{
171	/*
172	 * if next expires before rq, assign its expire time to rq
173	 * and move into next position (next will be deleted) in fifo
174	 */
175	if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
176		if (time_before((unsigned long)next->fifo_time,
177				(unsigned long)req->fifo_time)) {
178			list_move(&req->queuelist, &next->queuelist);
179			req->fifo_time = next->fifo_time;
180		}
181	}
182
183	/*
184	 * kill knowledge of next, this one is a goner
185	 */
186	deadline_remove_request(q, next);
187}
188
189/*
190 * move request from sort list to dispatch queue.
191 */
192static inline void
193deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
194{
195	struct request_queue *q = rq->q;
196
197	/*
198	 * For a zoned block device, write requests must write lock their
199	 * target zone.
200	 */
201	blk_req_zone_write_lock(rq);
202
203	deadline_remove_request(q, rq);
204	elv_dispatch_add_tail(q, rq);
205}
206
207/*
208 * move an entry to dispatch queue
209 */
210static void
211deadline_move_request(struct deadline_data *dd, struct request *rq)
212{
213	const int data_dir = rq_data_dir(rq);
214
215	dd->next_rq[READ] = NULL;
216	dd->next_rq[WRITE] = NULL;
217	dd->next_rq[data_dir] = deadline_latter_request(rq);
218
219	/*
220	 * take it off the sort and fifo list, move
221	 * to dispatch queue
222	 */
223	deadline_move_to_dispatch(dd, rq);
224}
225
226/*
227 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
228 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
229 */
230static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
231{
232	struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
233
234	/*
235	 * rq is expired!
236	 */
237	if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
238		return 1;
239
240	return 0;
241}
242
243/*
244 * For the specified data direction, return the next request to dispatch using
245 * arrival ordered lists.
246 */
247static struct request *
248deadline_fifo_request(struct deadline_data *dd, int data_dir)
249{
250	struct request *rq;
251
252	if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
253		return NULL;
254
255	if (list_empty(&dd->fifo_list[data_dir]))
256		return NULL;
257
258	rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
259	if (data_dir == READ || !blk_queue_is_zoned(rq->q))
260		return rq;
261
262	/*
263	 * Look for a write request that can be dispatched, that is one with
264	 * an unlocked target zone.
265	 */
266	list_for_each_entry(rq, &dd->fifo_list[WRITE], queuelist) {
267		if (blk_req_can_dispatch_to_zone(rq))
268			return rq;
269	}
270
271	return NULL;
272}
273
274/*
275 * For the specified data direction, return the next request to dispatch using
276 * sector position sorted lists.
277 */
278static struct request *
279deadline_next_request(struct deadline_data *dd, int data_dir)
280{
281	struct request *rq;
282
283	if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
284		return NULL;
285
286	rq = dd->next_rq[data_dir];
287	if (!rq)
288		return NULL;
289
290	if (data_dir == READ || !blk_queue_is_zoned(rq->q))
291		return rq;
292
293	/*
294	 * Look for a write request that can be dispatched, that is one with
295	 * an unlocked target zone.
296	 */
297	while (rq) {
298		if (blk_req_can_dispatch_to_zone(rq))
299			return rq;
300		rq = deadline_latter_request(rq);
301	}
302
303	return NULL;
304}
305
306/*
307 * deadline_dispatch_requests selects the best request according to
308 * read/write expire, fifo_batch, etc
309 */
310static int deadline_dispatch_requests(struct request_queue *q, int force)
311{
312	struct deadline_data *dd = q->elevator->elevator_data;
313	const int reads = !list_empty(&dd->fifo_list[READ]);
314	const int writes = !list_empty(&dd->fifo_list[WRITE]);
315	struct request *rq, *next_rq;
316	int data_dir;
317
318	/*
319	 * batches are currently reads XOR writes
320	 */
321	rq = deadline_next_request(dd, WRITE);
322	if (!rq)
323		rq = deadline_next_request(dd, READ);
324
325	if (rq && dd->batching < dd->fifo_batch)
326		/* we have a next request are still entitled to batch */
327		goto dispatch_request;
328
329	/*
330	 * at this point we are not running a batch. select the appropriate
331	 * data direction (read / write)
332	 */
333
334	if (reads) {
335		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
336
337		if (deadline_fifo_request(dd, WRITE) &&
338		    (dd->starved++ >= dd->writes_starved))
339			goto dispatch_writes;
340
341		data_dir = READ;
342
343		goto dispatch_find_request;
344	}
345
346	/*
347	 * there are either no reads or writes have been starved
348	 */
349
350	if (writes) {
351dispatch_writes:
352		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
353
354		dd->starved = 0;
355
356		data_dir = WRITE;
357
358		goto dispatch_find_request;
359	}
360
361	return 0;
362
363dispatch_find_request:
364	/*
365	 * we are not running a batch, find best request for selected data_dir
366	 */
367	next_rq = deadline_next_request(dd, data_dir);
368	if (deadline_check_fifo(dd, data_dir) || !next_rq) {
369		/*
370		 * A deadline has expired, the last request was in the other
371		 * direction, or we have run out of higher-sectored requests.
372		 * Start again from the request with the earliest expiry time.
373		 */
374		rq = deadline_fifo_request(dd, data_dir);
375	} else {
376		/*
377		 * The last req was the same dir and we have a next request in
378		 * sort order. No expired requests so continue on from here.
379		 */
380		rq = next_rq;
381	}
382
383	/*
384	 * For a zoned block device, if we only have writes queued and none of
385	 * them can be dispatched, rq will be NULL.
386	 */
387	if (!rq)
388		return 0;
389
390	dd->batching = 0;
391
392dispatch_request:
393	/*
394	 * rq is the selected appropriate request.
395	 */
396	dd->batching++;
397	deadline_move_request(dd, rq);
398
399	return 1;
400}
401
402/*
403 * For zoned block devices, write unlock the target zone of completed
404 * write requests.
405 */
406static void
407deadline_completed_request(struct request_queue *q, struct request *rq)
408{
409	blk_req_zone_write_unlock(rq);
410}
411
412static void deadline_exit_queue(struct elevator_queue *e)
413{
414	struct deadline_data *dd = e->elevator_data;
415
416	BUG_ON(!list_empty(&dd->fifo_list[READ]));
417	BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
418
419	kfree(dd);
420}
421
422/*
423 * initialize elevator private data (deadline_data).
424 */
425static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
426{
427	struct deadline_data *dd;
428	struct elevator_queue *eq;
429
430	eq = elevator_alloc(q, e);
431	if (!eq)
432		return -ENOMEM;
433
434	dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
435	if (!dd) {
436		kobject_put(&eq->kobj);
437		return -ENOMEM;
438	}
439	eq->elevator_data = dd;
440
441	INIT_LIST_HEAD(&dd->fifo_list[READ]);
442	INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
443	dd->sort_list[READ] = RB_ROOT;
444	dd->sort_list[WRITE] = RB_ROOT;
445	dd->fifo_expire[READ] = read_expire;
446	dd->fifo_expire[WRITE] = write_expire;
447	dd->writes_starved = writes_starved;
448	dd->front_merges = 1;
449	dd->fifo_batch = fifo_batch;
450
451	spin_lock_irq(q->queue_lock);
452	q->elevator = eq;
453	spin_unlock_irq(q->queue_lock);
454	return 0;
455}
456
457/*
458 * sysfs parts below
459 */
460
461static ssize_t
462deadline_var_show(int var, char *page)
463{
464	return sprintf(page, "%d\n", var);
465}
466
467static void
468deadline_var_store(int *var, const char *page)
469{
470	char *p = (char *) page;
471
472	*var = simple_strtol(p, &p, 10);
473}
474
475#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)				\
476static ssize_t __FUNC(struct elevator_queue *e, char *page)		\
477{									\
478	struct deadline_data *dd = e->elevator_data;			\
479	int __data = __VAR;						\
480	if (__CONV)							\
481		__data = jiffies_to_msecs(__data);			\
482	return deadline_var_show(__data, (page));			\
483}
484SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
485SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
486SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
487SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
488SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
489#undef SHOW_FUNCTION
490
491#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
492static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)	\
493{									\
494	struct deadline_data *dd = e->elevator_data;			\
495	int __data;							\
496	deadline_var_store(&__data, (page));				\
497	if (__data < (MIN))						\
498		__data = (MIN);						\
499	else if (__data > (MAX))					\
500		__data = (MAX);						\
501	if (__CONV)							\
502		*(__PTR) = msecs_to_jiffies(__data);			\
503	else								\
504		*(__PTR) = __data;					\
505	return count;							\
506}
507STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
508STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
509STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
510STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
511STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
512#undef STORE_FUNCTION
513
514#define DD_ATTR(name) \
515	__ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
516				      deadline_##name##_store)
517
518static struct elv_fs_entry deadline_attrs[] = {
519	DD_ATTR(read_expire),
520	DD_ATTR(write_expire),
521	DD_ATTR(writes_starved),
522	DD_ATTR(front_merges),
523	DD_ATTR(fifo_batch),
524	__ATTR_NULL
525};
526
527static struct elevator_type iosched_deadline = {
528	.ops.sq = {
529		.elevator_merge_fn = 		deadline_merge,
530		.elevator_merged_fn =		deadline_merged_request,
531		.elevator_merge_req_fn =	deadline_merged_requests,
532		.elevator_dispatch_fn =		deadline_dispatch_requests,
533		.elevator_completed_req_fn =	deadline_completed_request,
534		.elevator_add_req_fn =		deadline_add_request,
535		.elevator_former_req_fn =	elv_rb_former_request,
536		.elevator_latter_req_fn =	elv_rb_latter_request,
537		.elevator_init_fn =		deadline_init_queue,
538		.elevator_exit_fn =		deadline_exit_queue,
539	},
540
541	.elevator_attrs = deadline_attrs,
542	.elevator_name = "deadline",
543	.elevator_owner = THIS_MODULE,
544};
545
546static int __init deadline_init(void)
547{
548	return elv_register(&iosched_deadline);
549}
550
551static void __exit deadline_exit(void)
552{
553	elv_unregister(&iosched_deadline);
554}
555
556module_init(deadline_init);
557module_exit(deadline_exit);
558
559MODULE_AUTHOR("Jens Axboe");
560MODULE_LICENSE("GPL");
561MODULE_DESCRIPTION("deadline IO scheduler");