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 int
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 int ret;
129
130 /*
131 * check for front merge
132 */
133 if (dd->front_merges) {
134 sector_t sector = bio_end_sector(bio);
135
136 __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
137 if (__rq) {
138 BUG_ON(sector != blk_rq_pos(__rq));
139
140 if (elv_rq_merge_ok(__rq, bio)) {
141 ret = ELEVATOR_FRONT_MERGE;
142 goto out;
143 }
144 }
145 }
146
147 return ELEVATOR_NO_MERGE;
148 out:
149 *req = __rq;
150 return ret;
151 }
152
153 static void deadline_merged_request(struct request_queue *q,
154 struct request *req, int type)
155 {
156 struct deadline_data *dd = q->elevator->elevator_data;
157
158 /*
159 * if the merge was a front merge, we need to reposition request
160 */
161 if (type == ELEVATOR_FRONT_MERGE) {
162 elv_rb_del(deadline_rb_root(dd, req), req);
163 deadline_add_rq_rb(dd, req);
164 }
165 }
166
167 static void
168 deadline_merged_requests(struct request_queue *q, struct request *req,
169 struct request *next)
170 {
171 /*
172 * if next expires before rq, assign its expire time to rq
173 * and move into next position (next will be deleted) in fifo
174 */
175 if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
176 if (time_before(next->fifo_time, req->fifo_time)) {
177 list_move(&req->queuelist, &next->queuelist);
178 req->fifo_time = next->fifo_time;
179 }
180 }
181
182 /*
183 * kill knowledge of next, this one is a goner
184 */
185 deadline_remove_request(q, next);
186 }
187
188 /*
189 * move request from sort list to dispatch queue.
190 */
191 static inline void
192 deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
193 {
194 struct request_queue *q = rq->q;
195
196 deadline_remove_request(q, rq);
197 elv_dispatch_add_tail(q, rq);
198 }
199
200 /*
201 * move an entry to dispatch queue
202 */
203 static void
204 deadline_move_request(struct deadline_data *dd, struct request *rq)
205 {
206 const int data_dir = rq_data_dir(rq);
207
208 dd->next_rq[READ] = NULL;
209 dd->next_rq[WRITE] = NULL;
210 dd->next_rq[data_dir] = deadline_latter_request(rq);
211
212 /*
213 * take it off the sort and fifo list, move
214 * to dispatch queue
215 */
216 deadline_move_to_dispatch(dd, rq);
217 }
218
219 /*
220 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
221 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
222 */
223 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
224 {
225 struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
226
227 /*
228 * rq is expired!
229 */
230 if (time_after_eq(jiffies, rq->fifo_time))
231 return 1;
232
233 return 0;
234 }
235
236 /*
237 * deadline_dispatch_requests selects the best request according to
238 * read/write expire, fifo_batch, etc
239 */
240 static int deadline_dispatch_requests(struct request_queue *q, int force)
241 {
242 struct deadline_data *dd = q->elevator->elevator_data;
243 const int reads = !list_empty(&dd->fifo_list[READ]);
244 const int writes = !list_empty(&dd->fifo_list[WRITE]);
245 struct request *rq;
246 int data_dir;
247
248 /*
249 * batches are currently reads XOR writes
250 */
251 if (dd->next_rq[WRITE])
252 rq = dd->next_rq[WRITE];
253 else
254 rq = dd->next_rq[READ];
255
256 if (rq && dd->batching < dd->fifo_batch)
257 /* we have a next request are still entitled to batch */
258 goto dispatch_request;
259
260 /*
261 * at this point we are not running a batch. select the appropriate
262 * data direction (read / write)
263 */
264
265 if (reads) {
266 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
267
268 if (writes && (dd->starved++ >= dd->writes_starved))
269 goto dispatch_writes;
270
271 data_dir = READ;
272
273 goto dispatch_find_request;
274 }
275
276 /*
277 * there are either no reads or writes have been starved
278 */
279
280 if (writes) {
281 dispatch_writes:
282 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
283
284 dd->starved = 0;
285
286 data_dir = WRITE;
287
288 goto dispatch_find_request;
289 }
290
291 return 0;
292
293 dispatch_find_request:
294 /*
295 * we are not running a batch, find best request for selected data_dir
296 */
297 if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
298 /*
299 * A deadline has expired, the last request was in the other
300 * direction, or we have run out of higher-sectored requests.
301 * Start again from the request with the earliest expiry time.
302 */
303 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
304 } else {
305 /*
306 * The last req was the same dir and we have a next request in
307 * sort order. No expired requests so continue on from here.
308 */
309 rq = dd->next_rq[data_dir];
310 }
311
312 dd->batching = 0;
313
314 dispatch_request:
315 /*
316 * rq is the selected appropriate request.
317 */
318 dd->batching++;
319 deadline_move_request(dd, rq);
320
321 return 1;
322 }
323
324 static void deadline_exit_queue(struct elevator_queue *e)
325 {
326 struct deadline_data *dd = e->elevator_data;
327
328 BUG_ON(!list_empty(&dd->fifo_list[READ]));
329 BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
330
331 kfree(dd);
332 }
333
334 /*
335 * initialize elevator private data (deadline_data).
336 */
337 static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
338 {
339 struct deadline_data *dd;
340 struct elevator_queue *eq;
341
342 eq = elevator_alloc(q, e);
343 if (!eq)
344 return -ENOMEM;
345
346 dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
347 if (!dd) {
348 kobject_put(&eq->kobj);
349 return -ENOMEM;
350 }
351 eq->elevator_data = dd;
352
353 INIT_LIST_HEAD(&dd->fifo_list[READ]);
354 INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
355 dd->sort_list[READ] = RB_ROOT;
356 dd->sort_list[WRITE] = RB_ROOT;
357 dd->fifo_expire[READ] = read_expire;
358 dd->fifo_expire[WRITE] = write_expire;
359 dd->writes_starved = writes_starved;
360 dd->front_merges = 1;
361 dd->fifo_batch = fifo_batch;
362
363 spin_lock_irq(q->queue_lock);
364 q->elevator = eq;
365 spin_unlock_irq(q->queue_lock);
366 return 0;
367 }
368
369 /*
370 * sysfs parts below
371 */
372
373 static ssize_t
374 deadline_var_show(int var, char *page)
375 {
376 return sprintf(page, "%d\n", var);
377 }
378
379 static ssize_t
380 deadline_var_store(int *var, const char *page, size_t count)
381 {
382 char *p = (char *) page;
383
384 *var = simple_strtol(p, &p, 10);
385 return count;
386 }
387
388 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
389 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
390 { \
391 struct deadline_data *dd = e->elevator_data; \
392 int __data = __VAR; \
393 if (__CONV) \
394 __data = jiffies_to_msecs(__data); \
395 return deadline_var_show(__data, (page)); \
396 }
397 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
398 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
399 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
400 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
401 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
402 #undef SHOW_FUNCTION
403
404 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
405 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
406 { \
407 struct deadline_data *dd = e->elevator_data; \
408 int __data; \
409 int ret = deadline_var_store(&__data, (page), count); \
410 if (__data < (MIN)) \
411 __data = (MIN); \
412 else if (__data > (MAX)) \
413 __data = (MAX); \
414 if (__CONV) \
415 *(__PTR) = msecs_to_jiffies(__data); \
416 else \
417 *(__PTR) = __data; \
418 return ret; \
419 }
420 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
421 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
422 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
423 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
424 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
425 #undef STORE_FUNCTION
426
427 #define DD_ATTR(name) \
428 __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
429 deadline_##name##_store)
430
431 static struct elv_fs_entry deadline_attrs[] = {
432 DD_ATTR(read_expire),
433 DD_ATTR(write_expire),
434 DD_ATTR(writes_starved),
435 DD_ATTR(front_merges),
436 DD_ATTR(fifo_batch),
437 __ATTR_NULL
438 };
439
440 static struct elevator_type iosched_deadline = {
441 .ops = {
442 .elevator_merge_fn = deadline_merge,
443 .elevator_merged_fn = deadline_merged_request,
444 .elevator_merge_req_fn = deadline_merged_requests,
445 .elevator_dispatch_fn = deadline_dispatch_requests,
446 .elevator_add_req_fn = deadline_add_request,
447 .elevator_former_req_fn = elv_rb_former_request,
448 .elevator_latter_req_fn = elv_rb_latter_request,
449 .elevator_init_fn = deadline_init_queue,
450 .elevator_exit_fn = deadline_exit_queue,
451 },
452
453 .elevator_attrs = deadline_attrs,
454 .elevator_name = "deadline",
455 .elevator_owner = THIS_MODULE,
456 };
457
458 static int __init deadline_init(void)
459 {
460 return elv_register(&iosched_deadline);
461 }
462
463 static void __exit deadline_exit(void)
464 {
465 elv_unregister(&iosched_deadline);
466 }
467
468 module_init(deadline_init);
469 module_exit(deadline_exit);
470
471 MODULE_AUTHOR("Jens Axboe");
472 MODULE_LICENSE("GPL");
473 MODULE_DESCRIPTION("deadline IO scheduler");
474
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