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