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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_set_fifo_time(rq, 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->bi_sector + bio_sectors(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(rq_fifo_time(next), rq_fifo_time(req))) {
178 list_move(&req->queuelist, &next->queuelist);
179 rq_set_fifo_time(req, rq_fifo_time(next));
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(jiffies, rq_fifo_time(rq)))
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)
341{
342 struct deadline_data *dd;
343
344 dd = kmalloc_node(sizeof(*dd), GFP_KERNEL | __GFP_ZERO, q->node);
345 if (!dd)
346 return -ENOMEM;
347
348 INIT_LIST_HEAD(&dd->fifo_list[READ]);
349 INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
350 dd->sort_list[READ] = RB_ROOT;
351 dd->sort_list[WRITE] = RB_ROOT;
352 dd->fifo_expire[READ] = read_expire;
353 dd->fifo_expire[WRITE] = write_expire;
354 dd->writes_starved = writes_starved;
355 dd->front_merges = 1;
356 dd->fifo_batch = fifo_batch;
357
358 q->elevator->elevator_data = dd;
359 return 0;
360}
361
362/*
363 * sysfs parts below
364 */
365
366static ssize_t
367deadline_var_show(int var, char *page)
368{
369 return sprintf(page, "%d\n", var);
370}
371
372static ssize_t
373deadline_var_store(int *var, const char *page, size_t count)
374{
375 char *p = (char *) page;
376
377 *var = simple_strtol(p, &p, 10);
378 return count;
379}
380
381#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
382static ssize_t __FUNC(struct elevator_queue *e, char *page) \
383{ \
384 struct deadline_data *dd = e->elevator_data; \
385 int __data = __VAR; \
386 if (__CONV) \
387 __data = jiffies_to_msecs(__data); \
388 return deadline_var_show(__data, (page)); \
389}
390SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
391SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
392SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
393SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
394SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
395#undef SHOW_FUNCTION
396
397#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
398static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
399{ \
400 struct deadline_data *dd = e->elevator_data; \
401 int __data; \
402 int ret = deadline_var_store(&__data, (page), count); \
403 if (__data < (MIN)) \
404 __data = (MIN); \
405 else if (__data > (MAX)) \
406 __data = (MAX); \
407 if (__CONV) \
408 *(__PTR) = msecs_to_jiffies(__data); \
409 else \
410 *(__PTR) = __data; \
411 return ret; \
412}
413STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
414STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
415STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
416STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
417STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
418#undef STORE_FUNCTION
419
420#define DD_ATTR(name) \
421 __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
422 deadline_##name##_store)
423
424static struct elv_fs_entry deadline_attrs[] = {
425 DD_ATTR(read_expire),
426 DD_ATTR(write_expire),
427 DD_ATTR(writes_starved),
428 DD_ATTR(front_merges),
429 DD_ATTR(fifo_batch),
430 __ATTR_NULL
431};
432
433static struct elevator_type iosched_deadline = {
434 .ops = {
435 .elevator_merge_fn = deadline_merge,
436 .elevator_merged_fn = deadline_merged_request,
437 .elevator_merge_req_fn = deadline_merged_requests,
438 .elevator_dispatch_fn = deadline_dispatch_requests,
439 .elevator_add_req_fn = deadline_add_request,
440 .elevator_former_req_fn = elv_rb_former_request,
441 .elevator_latter_req_fn = elv_rb_latter_request,
442 .elevator_init_fn = deadline_init_queue,
443 .elevator_exit_fn = deadline_exit_queue,
444 },
445
446 .elevator_attrs = deadline_attrs,
447 .elevator_name = "deadline",
448 .elevator_owner = THIS_MODULE,
449};
450
451static int __init deadline_init(void)
452{
453 return elv_register(&iosched_deadline);
454}
455
456static void __exit deadline_exit(void)
457{
458 elv_unregister(&iosched_deadline);
459}
460
461module_init(deadline_init);
462module_exit(deadline_exit);
463
464MODULE_AUTHOR("Jens Axboe");
465MODULE_LICENSE("GPL");
466MODULE_DESCRIPTION("deadline IO scheduler");