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 */
20 static const int read_expire = HZ / 2; /* max time before a read is submitted. */
21 static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
22 static const int writes_starved = 2; /* max times reads can starve a write */
23 static const int fifo_batch = 16; /* # of sequential requests treated as one
24 by the above parameters. For throughput. */
25
26 struct 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
54 static void deadline_move_request(struct deadline_data *, struct request *);
55
56 #define RQ_RB_ROOT(dd, rq) (&(dd)->sort_list[rq_data_dir((rq))])
57
58 /*
59 * get the request after `rq' in sector-sorted order
60 */
61 static inline struct request *
62 deadline_latter_request(struct request *rq)
63 {
64 struct rb_node *node = rb_next(&rq->rb_node);
65
66 if (node)
67 return rb_entry_rq(node);
68
69 return NULL;
70 }
71
72 static void
73 deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
74 {
75 struct rb_root *root = RQ_RB_ROOT(dd, rq);
76 struct request *__alias;
77
78 retry:
79 __alias = elv_rb_add(root, rq);
80 if (unlikely(__alias)) {
81 deadline_move_request(dd, __alias);
82 goto retry;
83 }
84 }
85
86 static inline void
87 deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
88 {
89 const int data_dir = rq_data_dir(rq);
90
91 if (dd->next_rq[data_dir] == rq)
92 dd->next_rq[data_dir] = deadline_latter_request(rq);
93
94 elv_rb_del(RQ_RB_ROOT(dd, rq), rq);
95 }
96
97 /*
98 * add rq to rbtree and fifo
99 */
100 static void
101 deadline_add_request(struct request_queue *q, struct request *rq)
102 {
103 struct deadline_data *dd = q->elevator->elevator_data;
104 const int data_dir = rq_data_dir(rq);
105
106 deadline_add_rq_rb(dd, rq);
107
108 /*
109 * set expire time (only used for reads) and add to fifo list
110 */
111 rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
112 list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
113 }
114
115 /*
116 * remove rq from rbtree and fifo.
117 */
118 static void deadline_remove_request(struct request_queue *q, struct request *rq)
119 {
120 struct deadline_data *dd = q->elevator->elevator_data;
121
122 rq_fifo_clear(rq);
123 deadline_del_rq_rb(dd, rq);
124 }
125
126 static int
127 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
128 {
129 struct deadline_data *dd = q->elevator->elevator_data;
130 struct request *__rq;
131 int ret;
132
133 /*
134 * check for front merge
135 */
136 if (dd->front_merges) {
137 sector_t sector = bio->bi_sector + bio_sectors(bio);
138
139 __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
140 if (__rq) {
141 BUG_ON(sector != __rq->sector);
142
143 if (elv_rq_merge_ok(__rq, bio)) {
144 ret = ELEVATOR_FRONT_MERGE;
145 goto out;
146 }
147 }
148 }
149
150 return ELEVATOR_NO_MERGE;
151 out:
152 *req = __rq;
153 return ret;
154 }
155
156 static void deadline_merged_request(struct request_queue *q,
157 struct request *req, int type)
158 {
159 struct deadline_data *dd = q->elevator->elevator_data;
160
161 /*
162 * if the merge was a front merge, we need to reposition request
163 */
164 if (type == ELEVATOR_FRONT_MERGE) {
165 elv_rb_del(RQ_RB_ROOT(dd, req), req);
166 deadline_add_rq_rb(dd, req);
167 }
168 }
169
170 static void
171 deadline_merged_requests(struct request_queue *q, struct request *req,
172 struct request *next)
173 {
174 /*
175 * if next expires before rq, assign its expire time to rq
176 * and move into next position (next will be deleted) in fifo
177 */
178 if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
179 if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
180 list_move(&req->queuelist, &next->queuelist);
181 rq_set_fifo_time(req, rq_fifo_time(next));
182 }
183 }
184
185 /*
186 * kill knowledge of next, this one is a goner
187 */
188 deadline_remove_request(q, next);
189 }
190
191 /*
192 * move request from sort list to dispatch queue.
193 */
194 static inline void
195 deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
196 {
197 struct request_queue *q = rq->q;
198
199 deadline_remove_request(q, rq);
200 elv_dispatch_add_tail(q, rq);
201 }
202
203 /*
204 * move an entry to dispatch queue
205 */
206 static void
207 deadline_move_request(struct deadline_data *dd, struct request *rq)
208 {
209 const int data_dir = rq_data_dir(rq);
210
211 dd->next_rq[READ] = NULL;
212 dd->next_rq[WRITE] = NULL;
213 dd->next_rq[data_dir] = deadline_latter_request(rq);
214
215 dd->last_sector = rq->sector + rq->nr_sectors;
216
217 /*
218 * take it off the sort and fifo list, move
219 * to dispatch queue
220 */
221 deadline_move_to_dispatch(dd, rq);
222 }
223
224 /*
225 * deadline_check_fifo returns 0 if there are no expired reads on the fifo,
226 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
227 */
228 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
229 {
230 struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
231
232 /*
233 * rq is expired!
234 */
235 if (time_after(jiffies, rq_fifo_time(rq)))
236 return 1;
237
238 return 0;
239 }
240
241 /*
242 * deadline_dispatch_requests selects the best request according to
243 * read/write expire, fifo_batch, etc
244 */
245 static int deadline_dispatch_requests(struct request_queue *q, int force)
246 {
247 struct deadline_data *dd = q->elevator->elevator_data;
248 const int reads = !list_empty(&dd->fifo_list[READ]);
249 const int writes = !list_empty(&dd->fifo_list[WRITE]);
250 struct request *rq;
251 int data_dir;
252
253 /*
254 * batches are currently reads XOR writes
255 */
256 if (dd->next_rq[WRITE])
257 rq = dd->next_rq[WRITE];
258 else
259 rq = dd->next_rq[READ];
260
261 if (rq) {
262 /* we have a "next request" */
263
264 if (dd->last_sector != rq->sector)
265 /* end the batch on a non sequential request */
266 dd->batching += dd->fifo_batch;
267
268 if (dd->batching < dd->fifo_batch)
269 /* we are still entitled to batch */
270 goto dispatch_request;
271 }
272
273 /*
274 * at this point we are not running a batch. select the appropriate
275 * data direction (read / write)
276 */
277
278 if (reads) {
279 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
280
281 if (writes && (dd->starved++ >= dd->writes_starved))
282 goto dispatch_writes;
283
284 data_dir = READ;
285
286 goto dispatch_find_request;
287 }
288
289 /*
290 * there are either no reads or writes have been starved
291 */
292
293 if (writes) {
294 dispatch_writes:
295 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
296
297 dd->starved = 0;
298
299 data_dir = WRITE;
300
301 goto dispatch_find_request;
302 }
303
304 return 0;
305
306 dispatch_find_request:
307 /*
308 * we are not running a batch, find best request for selected data_dir
309 */
310 if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
311 /*
312 * A deadline has expired, the last request was in the other
313 * direction, or we have run out of higher-sectored requests.
314 * Start again from the request with the earliest expiry time.
315 */
316 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
317 } else {
318 /*
319 * The last req was the same dir and we have a next request in
320 * sort order. No expired requests so continue on from here.
321 */
322 rq = dd->next_rq[data_dir];
323 }
324
325 dd->batching = 0;
326
327 dispatch_request:
328 /*
329 * rq is the selected appropriate request.
330 */
331 dd->batching++;
332 deadline_move_request(dd, rq);
333
334 return 1;
335 }
336
337 static int deadline_queue_empty(struct request_queue *q)
338 {
339 struct deadline_data *dd = q->elevator->elevator_data;
340
341 return list_empty(&dd->fifo_list[WRITE])
342 && list_empty(&dd->fifo_list[READ]);
343 }
344
345 static void deadline_exit_queue(elevator_t *e)
346 {
347 struct deadline_data *dd = e->elevator_data;
348
349 BUG_ON(!list_empty(&dd->fifo_list[READ]));
350 BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
351
352 kfree(dd);
353 }
354
355 /*
356 * initialize elevator private data (deadline_data).
357 */
358 static void *deadline_init_queue(struct request_queue *q)
359 {
360 struct deadline_data *dd;
361
362 dd = kmalloc_node(sizeof(*dd), GFP_KERNEL | __GFP_ZERO, q->node);
363 if (!dd)
364 return NULL;
365
366 INIT_LIST_HEAD(&dd->fifo_list[READ]);
367 INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
368 dd->sort_list[READ] = RB_ROOT;
369 dd->sort_list[WRITE] = RB_ROOT;
370 dd->fifo_expire[READ] = read_expire;
371 dd->fifo_expire[WRITE] = write_expire;
372 dd->writes_starved = writes_starved;
373 dd->front_merges = 1;
374 dd->fifo_batch = fifo_batch;
375 return dd;
376 }
377
378 /*
379 * sysfs parts below
380 */
381
382 static ssize_t
383 deadline_var_show(int var, char *page)
384 {
385 return sprintf(page, "%d\n", var);
386 }
387
388 static ssize_t
389 deadline_var_store(int *var, const char *page, size_t count)
390 {
391 char *p = (char *) page;
392
393 *var = simple_strtol(p, &p, 10);
394 return count;
395 }
396
397 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
398 static ssize_t __FUNC(elevator_t *e, char *page) \
399 { \
400 struct deadline_data *dd = e->elevator_data; \
401 int __data = __VAR; \
402 if (__CONV) \
403 __data = jiffies_to_msecs(__data); \
404 return deadline_var_show(__data, (page)); \
405 }
406 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
407 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
408 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
409 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
410 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
411 #undef SHOW_FUNCTION
412
413 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
414 static ssize_t __FUNC(elevator_t *e, const char *page, size_t count) \
415 { \
416 struct deadline_data *dd = e->elevator_data; \
417 int __data; \
418 int ret = deadline_var_store(&__data, (page), count); \
419 if (__data < (MIN)) \
420 __data = (MIN); \
421 else if (__data > (MAX)) \
422 __data = (MAX); \
423 if (__CONV) \
424 *(__PTR) = msecs_to_jiffies(__data); \
425 else \
426 *(__PTR) = __data; \
427 return ret; \
428 }
429 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
430 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
431 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
432 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
433 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
434 #undef STORE_FUNCTION
435
436 #define DD_ATTR(name) \
437 __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
438 deadline_##name##_store)
439
440 static struct elv_fs_entry deadline_attrs[] = {
441 DD_ATTR(read_expire),
442 DD_ATTR(write_expire),
443 DD_ATTR(writes_starved),
444 DD_ATTR(front_merges),
445 DD_ATTR(fifo_batch),
446 __ATTR_NULL
447 };
448
449 static struct elevator_type iosched_deadline = {
450 .ops = {
451 .elevator_merge_fn = deadline_merge,
452 .elevator_merged_fn = deadline_merged_request,
453 .elevator_merge_req_fn = deadline_merged_requests,
454 .elevator_dispatch_fn = deadline_dispatch_requests,
455 .elevator_add_req_fn = deadline_add_request,
456 .elevator_queue_empty_fn = deadline_queue_empty,
457 .elevator_former_req_fn = elv_rb_former_request,
458 .elevator_latter_req_fn = elv_rb_latter_request,
459 .elevator_init_fn = deadline_init_queue,
460 .elevator_exit_fn = deadline_exit_queue,
461 },
462
463 .elevator_attrs = deadline_attrs,
464 .elevator_name = "deadline",
465 .elevator_owner = THIS_MODULE,
466 };
467
468 static int __init deadline_init(void)
469 {
470 elv_register(&iosched_deadline);
471
472 return 0;
473 }
474
475 static void __exit deadline_exit(void)
476 {
477 elv_unregister(&iosched_deadline);
478 }
479
480 module_init(deadline_init);
481 module_exit(deadline_exit);
482
483 MODULE_AUTHOR("Jens Axboe");
484 MODULE_LICENSE("GPL");
485 MODULE_DESCRIPTION("deadline IO scheduler");
486
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