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	sector_t last_sector;		/* head position */
43	unsigned int starved;		/* times reads have starved writes */
44
45	/*
46	 * settings that change how the i/o scheduler behaves
47	 */
48	int fifo_expire[2];
49	int fifo_batch;
50	int writes_starved;
51	int front_merges;
52};
53
54static void deadline_move_request(struct deadline_data *, struct request *);
55
56static inline struct rb_root *
57deadline_rb_root(struct deadline_data *dd, struct request *rq)
58{
59	return &dd->sort_list[rq_data_dir(rq)];
60}
61
62/*
63 * get the request after `rq' in sector-sorted order
64 */
65static inline struct request *
66deadline_latter_request(struct request *rq)
67{
68	struct rb_node *node = rb_next(&rq->rb_node);
69
70	if (node)
71		return rb_entry_rq(node);
72
73	return NULL;
74}
75
76static void
77deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
78{
79	struct rb_root *root = deadline_rb_root(dd, rq);
80
81	elv_rb_add(root, rq);
82}
83
84static inline void
85deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
86{
87	const int data_dir = rq_data_dir(rq);
88
89	if (dd->next_rq[data_dir] == rq)
90		dd->next_rq[data_dir] = deadline_latter_request(rq);
91
92	elv_rb_del(deadline_rb_root(dd, rq), rq);
93}
94
95/*
96 * add rq to rbtree and fifo
97 */
98static void
99deadline_add_request(struct request_queue *q, struct request *rq)
100{
101	struct deadline_data *dd = q->elevator->elevator_data;
102	const int data_dir = rq_data_dir(rq);
103
104	deadline_add_rq_rb(dd, rq);
105
106	/*
107	 * set expire time and add to fifo list
108	 */
109	rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
110	list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
111}
112
113/*
114 * remove rq from rbtree and fifo.
115 */
116static void deadline_remove_request(struct request_queue *q, struct request *rq)
117{
118	struct deadline_data *dd = q->elevator->elevator_data;
119
120	rq_fifo_clear(rq);
121	deadline_del_rq_rb(dd, rq);
122}
123
124static int
125deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
126{
127	struct deadline_data *dd = q->elevator->elevator_data;
128	struct request *__rq;
129	int ret;
130
131	/*
132	 * check for front merge
133	 */
134	if (dd->front_merges) {
135		sector_t sector = bio_end_sector(bio);
136
137		__rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
138		if (__rq) {
139			BUG_ON(sector != blk_rq_pos(__rq));
140
141			if (elv_rq_merge_ok(__rq, bio)) {
142				ret = ELEVATOR_FRONT_MERGE;
143				goto out;
144			}
145		}
146	}
147
148	return ELEVATOR_NO_MERGE;
149out:
150	*req = __rq;
151	return ret;
152}
153
154static void deadline_merged_request(struct request_queue *q,
155				    struct request *req, int type)
156{
157	struct deadline_data *dd = q->elevator->elevator_data;
158
159	/*
160	 * if the merge was a front merge, we need to reposition request
161	 */
162	if (type == ELEVATOR_FRONT_MERGE) {
163		elv_rb_del(deadline_rb_root(dd, req), req);
164		deadline_add_rq_rb(dd, req);
165	}
166}
167
168static void
169deadline_merged_requests(struct request_queue *q, struct request *req,
170			 struct request *next)
171{
172	/*
173	 * if next expires before rq, assign its expire time to rq
174	 * and move into next position (next will be deleted) in fifo
175	 */
176	if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
177		if (time_before(next->fifo_time, 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	deadline_remove_request(q, rq);
198	elv_dispatch_add_tail(q, rq);
199}
200
201/*
202 * move an entry to dispatch queue
203 */
204static void
205deadline_move_request(struct deadline_data *dd, struct request *rq)
206{
207	const int data_dir = rq_data_dir(rq);
208
209	dd->next_rq[READ] = NULL;
210	dd->next_rq[WRITE] = NULL;
211	dd->next_rq[data_dir] = deadline_latter_request(rq);
212
213	dd->last_sector = rq_end_sector(rq);
214
215	/*
216	 * take it off the sort and fifo list, move
217	 * to dispatch queue
218	 */
219	deadline_move_to_dispatch(dd, rq);
220}
221
222/*
223 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
224 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
225 */
226static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
227{
228	struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
229
230	/*
231	 * rq is expired!
232	 */
233	if (time_after_eq(jiffies, rq->fifo_time))
234		return 1;
235
236	return 0;
237}
238
239/*
240 * deadline_dispatch_requests selects the best request according to
241 * read/write expire, fifo_batch, etc
242 */
243static int deadline_dispatch_requests(struct request_queue *q, int force)
244{
245	struct deadline_data *dd = q->elevator->elevator_data;
246	const int reads = !list_empty(&dd->fifo_list[READ]);
247	const int writes = !list_empty(&dd->fifo_list[WRITE]);
248	struct request *rq;
249	int data_dir;
250
251	/*
252	 * batches are currently reads XOR writes
253	 */
254	if (dd->next_rq[WRITE])
255		rq = dd->next_rq[WRITE];
256	else
257		rq = dd->next_rq[READ];
258
259	if (rq && dd->batching < dd->fifo_batch)
260		/* we have a next request are still entitled to batch */
261		goto dispatch_request;
262
263	/*
264	 * at this point we are not running a batch. select the appropriate
265	 * data direction (read / write)
266	 */
267
268	if (reads) {
269		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
270
271		if (writes && (dd->starved++ >= dd->writes_starved))
272			goto dispatch_writes;
273
274		data_dir = READ;
275
276		goto dispatch_find_request;
277	}
278
279	/*
280	 * there are either no reads or writes have been starved
281	 */
282
283	if (writes) {
284dispatch_writes:
285		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
286
287		dd->starved = 0;
288
289		data_dir = WRITE;
290
291		goto dispatch_find_request;
292	}
293
294	return 0;
295
296dispatch_find_request:
297	/*
298	 * we are not running a batch, find best request for selected data_dir
299	 */
300	if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
301		/*
302		 * A deadline has expired, the last request was in the other
303		 * direction, or we have run out of higher-sectored requests.
304		 * Start again from the request with the earliest expiry time.
305		 */
306		rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
307	} else {
308		/*
309		 * The last req was the same dir and we have a next request in
310		 * sort order. No expired requests so continue on from here.
311		 */
312		rq = dd->next_rq[data_dir];
313	}
314
315	dd->batching = 0;
316
317dispatch_request:
318	/*
319	 * rq is the selected appropriate request.
320	 */
321	dd->batching++;
322	deadline_move_request(dd, rq);
323
324	return 1;
325}
326
327static void deadline_exit_queue(struct elevator_queue *e)
328{
329	struct deadline_data *dd = e->elevator_data;
330
331	BUG_ON(!list_empty(&dd->fifo_list[READ]));
332	BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
333
334	kfree(dd);
335}
336
337/*
338 * initialize elevator private data (deadline_data).
339 */
340static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
341{
342	struct deadline_data *dd;
343	struct elevator_queue *eq;
344
345	eq = elevator_alloc(q, e);
346	if (!eq)
347		return -ENOMEM;
348
349	dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
350	if (!dd) {
351		kobject_put(&eq->kobj);
352		return -ENOMEM;
353	}
354	eq->elevator_data = dd;
355
356	INIT_LIST_HEAD(&dd->fifo_list[READ]);
357	INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
358	dd->sort_list[READ] = RB_ROOT;
359	dd->sort_list[WRITE] = RB_ROOT;
360	dd->fifo_expire[READ] = read_expire;
361	dd->fifo_expire[WRITE] = write_expire;
362	dd->writes_starved = writes_starved;
363	dd->front_merges = 1;
364	dd->fifo_batch = fifo_batch;
365
366	spin_lock_irq(q->queue_lock);
367	q->elevator = eq;
368	spin_unlock_irq(q->queue_lock);
369	return 0;
370}
371
372/*
373 * sysfs parts below
374 */
375
376static ssize_t
377deadline_var_show(int var, char *page)
378{
379	return sprintf(page, "%d\n", var);
380}
381
382static ssize_t
383deadline_var_store(int *var, const char *page, size_t count)
384{
385	char *p = (char *) page;
386
387	*var = simple_strtol(p, &p, 10);
388	return count;
389}
390
391#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)				\
392static ssize_t __FUNC(struct elevator_queue *e, char *page)		\
393{									\
394	struct deadline_data *dd = e->elevator_data;			\
395	int __data = __VAR;						\
396	if (__CONV)							\
397		__data = jiffies_to_msecs(__data);			\
398	return deadline_var_show(__data, (page));			\
399}
400SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
401SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
402SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
403SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
404SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
405#undef SHOW_FUNCTION
406
407#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
408static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)	\
409{									\
410	struct deadline_data *dd = e->elevator_data;			\
411	int __data;							\
412	int ret = deadline_var_store(&__data, (page), count);		\
413	if (__data < (MIN))						\
414		__data = (MIN);						\
415	else if (__data > (MAX))					\
416		__data = (MAX);						\
417	if (__CONV)							\
418		*(__PTR) = msecs_to_jiffies(__data);			\
419	else								\
420		*(__PTR) = __data;					\
421	return ret;							\
422}
423STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
424STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
425STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
426STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
427STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
428#undef STORE_FUNCTION
429
430#define DD_ATTR(name) \
431	__ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
432				      deadline_##name##_store)
433
434static struct elv_fs_entry deadline_attrs[] = {
435	DD_ATTR(read_expire),
436	DD_ATTR(write_expire),
437	DD_ATTR(writes_starved),
438	DD_ATTR(front_merges),
439	DD_ATTR(fifo_batch),
440	__ATTR_NULL
441};
442
443static struct elevator_type iosched_deadline = {
444	.ops = {
445		.elevator_merge_fn = 		deadline_merge,
446		.elevator_merged_fn =		deadline_merged_request,
447		.elevator_merge_req_fn =	deadline_merged_requests,
448		.elevator_dispatch_fn =		deadline_dispatch_requests,
449		.elevator_add_req_fn =		deadline_add_request,
450		.elevator_former_req_fn =	elv_rb_former_request,
451		.elevator_latter_req_fn =	elv_rb_latter_request,
452		.elevator_init_fn =		deadline_init_queue,
453		.elevator_exit_fn =		deadline_exit_queue,
454	},
455
456	.elevator_attrs = deadline_attrs,
457	.elevator_name = "deadline",
458	.elevator_owner = THIS_MODULE,
459};
460
461static int __init deadline_init(void)
462{
463	return elv_register(&iosched_deadline);
464}
465
466static void __exit deadline_exit(void)
467{
468	elv_unregister(&iosched_deadline);
469}
470
471module_init(deadline_init);
472module_exit(deadline_exit);
473
474MODULE_AUTHOR("Jens Axboe");
475MODULE_LICENSE("GPL");
476MODULE_DESCRIPTION("deadline IO scheduler");
477