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1da177e4 1/*
1da177e4
LT
2 * Deadline i/o scheduler.
3 *
0fe23479 4 * Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
1da177e4
LT
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>
1da177e4
LT
11#include <linux/module.h>
12#include <linux/slab.h>
13#include <linux/init.h>
14#include <linux/compiler.h>
1da177e4
LT
15#include <linux/rbtree.h>
16
17/*
18 * See Documentation/block/deadline-iosched.txt
19 */
64100099
AV
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
1da177e4
LT
24 by the above parameters. For throughput. */
25
1da177e4
LT
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];
4fb72f76 36
1da177e4
LT
37 /*
38 * next in sort order. read, write or both are NULL
39 */
8840faa1 40 struct request *next_rq[2];
1da177e4
LT
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;
1da177e4
LT
52};
53
8840faa1 54static void deadline_move_request(struct deadline_data *, struct request *);
1da177e4 55
4fb72f76
AC
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}
1da177e4 61
5d1a5366
AC
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
1da177e4 76static void
8840faa1 77deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
1da177e4 78{
4fb72f76 79 struct rb_root *root = deadline_rb_root(dd, rq);
b8aca35a 80 struct request *__alias;
1da177e4 81
4fb72f76 82 while (unlikely(__alias = elv_rb_add(root, rq)))
8840faa1 83 deadline_move_request(dd, __alias);
1da177e4
LT
84}
85
86static inline void
8840faa1 87deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
1da177e4 88{
b8aca35a 89 const int data_dir = rq_data_dir(rq);
1da177e4 90
5d1a5366
AC
91 if (dd->next_rq[data_dir] == rq)
92 dd->next_rq[data_dir] = deadline_latter_request(rq);
1da177e4 93
4fb72f76 94 elv_rb_del(deadline_rb_root(dd, rq), rq);
1da177e4
LT
95}
96
97/*
8840faa1 98 * add rq to rbtree and fifo
1da177e4 99 */
b4878f24 100static void
1da177e4
LT
101deadline_add_request(struct request_queue *q, struct request *rq)
102{
103 struct deadline_data *dd = q->elevator->elevator_data;
8840faa1 104 const int data_dir = rq_data_dir(rq);
1da177e4 105
8840faa1 106 deadline_add_rq_rb(dd, rq);
9817064b 107
1da177e4 108 /*
4fb72f76 109 * set expire time and add to fifo list
1da177e4 110 */
8840faa1
JA
111 rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
112 list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
1da177e4
LT
113}
114
115/*
9817064b 116 * remove rq from rbtree and fifo.
1da177e4 117 */
165125e1 118static void deadline_remove_request(struct request_queue *q, struct request *rq)
1da177e4 119{
b4878f24 120 struct deadline_data *dd = q->elevator->elevator_data;
1da177e4 121
8840faa1
JA
122 rq_fifo_clear(rq);
123 deadline_del_rq_rb(dd, rq);
1da177e4
LT
124}
125
126static int
165125e1 127deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
1da177e4
LT
128{
129 struct deadline_data *dd = q->elevator->elevator_data;
130 struct request *__rq;
131 int ret;
132
1da177e4
LT
133 /*
134 * check for front merge
135 */
136 if (dd->front_merges) {
b8aca35a 137 sector_t sector = bio->bi_sector + bio_sectors(bio);
1da177e4 138
b8aca35a 139 __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
1da177e4 140 if (__rq) {
83096ebf 141 BUG_ON(sector != blk_rq_pos(__rq));
1da177e4
LT
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;
151out:
1da177e4
LT
152 *req = __rq;
153 return ret;
154}
155
165125e1
JA
156static void deadline_merged_request(struct request_queue *q,
157 struct request *req, int type)
1da177e4
LT
158{
159 struct deadline_data *dd = q->elevator->elevator_data;
1da177e4 160
1da177e4
LT
161 /*
162 * if the merge was a front merge, we need to reposition request
163 */
b8aca35a 164 if (type == ELEVATOR_FRONT_MERGE) {
4fb72f76 165 elv_rb_del(deadline_rb_root(dd, req), req);
8840faa1 166 deadline_add_rq_rb(dd, req);
1da177e4 167 }
1da177e4
LT
168}
169
170static void
165125e1 171deadline_merged_requests(struct request_queue *q, struct request *req,
1da177e4
LT
172 struct request *next)
173{
1da177e4 174 /*
8840faa1
JA
175 * if next expires before rq, assign its expire time to rq
176 * and move into next position (next will be deleted) in fifo
1da177e4 177 */
8840faa1
JA
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));
1da177e4
LT
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 */
194static inline void
8840faa1 195deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
1da177e4 196{
165125e1 197 struct request_queue *q = rq->q;
1da177e4 198
8840faa1
JA
199 deadline_remove_request(q, rq);
200 elv_dispatch_add_tail(q, rq);
1da177e4
LT
201}
202
203/*
204 * move an entry to dispatch queue
205 */
206static void
8840faa1 207deadline_move_request(struct deadline_data *dd, struct request *rq)
1da177e4 208{
b8aca35a 209 const int data_dir = rq_data_dir(rq);
1da177e4 210
8840faa1
JA
211 dd->next_rq[READ] = NULL;
212 dd->next_rq[WRITE] = NULL;
5d1a5366 213 dd->next_rq[data_dir] = deadline_latter_request(rq);
1da177e4 214
4fb72f76 215 dd->last_sector = rq_end_sector(rq);
1da177e4
LT
216
217 /*
218 * take it off the sort and fifo list, move
219 * to dispatch queue
220 */
8840faa1 221 deadline_move_to_dispatch(dd, rq);
1da177e4
LT
222}
223
1da177e4 224/*
4fb72f76 225 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
1da177e4
LT
226 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
227 */
228static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
229{
8840faa1 230 struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
1da177e4
LT
231
232 /*
8840faa1 233 * rq is expired!
1da177e4 234 */
8840faa1 235 if (time_after(jiffies, rq_fifo_time(rq)))
1da177e4
LT
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 */
165125e1 245static int deadline_dispatch_requests(struct request_queue *q, int force)
1da177e4 246{
b4878f24 247 struct deadline_data *dd = q->elevator->elevator_data;
1da177e4
LT
248 const int reads = !list_empty(&dd->fifo_list[READ]);
249 const int writes = !list_empty(&dd->fifo_list[WRITE]);
8840faa1 250 struct request *rq;
4b0dc07e 251 int data_dir;
1da177e4
LT
252
253 /*
254 * batches are currently reads XOR writes
255 */
8840faa1
JA
256 if (dd->next_rq[WRITE])
257 rq = dd->next_rq[WRITE];
9d5c1e1b 258 else
8840faa1 259 rq = dd->next_rq[READ];
1da177e4 260
63de428b
AC
261 if (rq && dd->batching < dd->fifo_batch)
262 /* we have a next request are still entitled to batch */
263 goto dispatch_request;
1da177e4
LT
264
265 /*
266 * at this point we are not running a batch. select the appropriate
267 * data direction (read / write)
268 */
269
270 if (reads) {
dd67d051 271 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
1da177e4
LT
272
273 if (writes && (dd->starved++ >= dd->writes_starved))
274 goto dispatch_writes;
275
276 data_dir = READ;
1da177e4
LT
277
278 goto dispatch_find_request;
279 }
280
281 /*
282 * there are either no reads or writes have been starved
283 */
284
285 if (writes) {
286dispatch_writes:
dd67d051 287 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
1da177e4
LT
288
289 dd->starved = 0;
290
291 data_dir = WRITE;
1da177e4
LT
292
293 goto dispatch_find_request;
294 }
295
296 return 0;
297
298dispatch_find_request:
299 /*
300 * we are not running a batch, find best request for selected data_dir
301 */
6f5d8aa6
AC
302 if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
303 /*
304 * A deadline has expired, the last request was in the other
305 * direction, or we have run out of higher-sectored requests.
306 * Start again from the request with the earliest expiry time.
307 */
8840faa1 308 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
6f5d8aa6 309 } else {
1da177e4
LT
310 /*
311 * The last req was the same dir and we have a next request in
312 * sort order. No expired requests so continue on from here.
313 */
8840faa1 314 rq = dd->next_rq[data_dir];
1da177e4
LT
315 }
316
dfb3d72a
AC
317 dd->batching = 0;
318
1da177e4
LT
319dispatch_request:
320 /*
8840faa1 321 * rq is the selected appropriate request.
1da177e4
LT
322 */
323 dd->batching++;
8840faa1 324 deadline_move_request(dd, rq);
1da177e4
LT
325
326 return 1;
327}
328
b374d18a 329static void deadline_exit_queue(struct elevator_queue *e)
1da177e4
LT
330{
331 struct deadline_data *dd = e->elevator_data;
332
333 BUG_ON(!list_empty(&dd->fifo_list[READ]));
334 BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
335
1da177e4
LT
336 kfree(dd);
337}
338
339/*
8840faa1 340 * initialize elevator private data (deadline_data).
1da177e4 341 */
165125e1 342static void *deadline_init_queue(struct request_queue *q)
1da177e4
LT
343{
344 struct deadline_data *dd;
1da177e4 345
94f6030c 346 dd = kmalloc_node(sizeof(*dd), GFP_KERNEL | __GFP_ZERO, q->node);
1da177e4 347 if (!dd)
bc1c1169 348 return NULL;
1da177e4 349
1da177e4
LT
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;
1da177e4
LT
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;
bc1c1169 359 return dd;
1da177e4
LT
360}
361
1da177e4
LT
362/*
363 * sysfs parts below
364 */
1da177e4
LT
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) \
b374d18a 382static ssize_t __FUNC(struct elevator_queue *e, char *page) \
1da177e4 383{ \
3d1ab40f
AV
384 struct deadline_data *dd = e->elevator_data; \
385 int __data = __VAR; \
1da177e4
LT
386 if (__CONV) \
387 __data = jiffies_to_msecs(__data); \
388 return deadline_var_show(__data, (page)); \
389}
e572ec7e
AV
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);
1da177e4
LT
395#undef SHOW_FUNCTION
396
397#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
b374d18a 398static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
1da177e4 399{ \
3d1ab40f 400 struct deadline_data *dd = e->elevator_data; \
1da177e4
LT
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}
e572ec7e
AV
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);
1da177e4
LT
418#undef STORE_FUNCTION
419
e572ec7e
AV
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
1da177e4
LT
431};
432
1da177e4
LT
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,
b4878f24
JA
438 .elevator_dispatch_fn = deadline_dispatch_requests,
439 .elevator_add_req_fn = deadline_add_request,
b8aca35a
JA
440 .elevator_former_req_fn = elv_rb_former_request,
441 .elevator_latter_req_fn = elv_rb_latter_request,
1da177e4
LT
442 .elevator_init_fn = deadline_init_queue,
443 .elevator_exit_fn = deadline_exit_queue,
444 },
445
3d1ab40f 446 .elevator_attrs = deadline_attrs,
1da177e4
LT
447 .elevator_name = "deadline",
448 .elevator_owner = THIS_MODULE,
449};
450
451static int __init deadline_init(void)
452{
2fdd82bd
AB
453 elv_register(&iosched_deadline);
454
455 return 0;
1da177e4
LT
456}
457
458static void __exit deadline_exit(void)
459{
1da177e4
LT
460 elv_unregister(&iosched_deadline);
461}
462
463module_init(deadline_init);
464module_exit(deadline_exit);
465
466MODULE_AUTHOR("Jens Axboe");
467MODULE_LICENSE("GPL");
468MODULE_DESCRIPTION("deadline IO scheduler");