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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 */
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 static inline struct rb_root *
57 deadline_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 */
65 static inline struct request *
66 deadline_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
76 static void
77 deadline_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
84 static inline void
85 deadline_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 */
98 static void
99 deadline_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 */
116 static 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
124 static int
125 deadline_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;
149 out:
150 *req = __rq;
151 return ret;
152 }
153
154 static 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
168 static void
169 deadline_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 */
192 static inline void
193 deadline_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 */
204 static void
205 deadline_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 */
226 static 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 */
243 static 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) {
284 dispatch_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
296 dispatch_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
317 dispatch_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
327 static 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 */
340 static 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
376 static ssize_t
377 deadline_var_show(int var, char *page)
378 {
379 return sprintf(page, "%d\n", var);
380 }
381
382 static ssize_t
383 deadline_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) \
392 static 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 }
400 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
401 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
402 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
403 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
404 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
405 #undef SHOW_FUNCTION
406
407 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
408 static 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 }
423 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
424 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
425 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
426 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
427 STORE_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
434 static 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
443 static 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
461 static int __init deadline_init(void)
462 {
463 return elv_register(&iosched_deadline);
464 }
465
466 static void __exit deadline_exit(void)
467 {
468 elv_unregister(&iosched_deadline);
469 }
470
471 module_init(deadline_init);
472 module_exit(deadline_exit);
473
474 MODULE_AUTHOR("Jens Axboe");
475 MODULE_LICENSE("GPL");
476 MODULE_DESCRIPTION("deadline IO scheduler");