2 * Deadline i/o scheduler.
4 * Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
6 #include <linux/kernel.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>
18 * See Documentation/block/deadline-iosched.txt
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. */
26 struct deadline_data {
32 * requests (deadline_rq s) are present on both sort_list and fifo_list
34 struct rb_root sort_list[2];
35 struct list_head fifo_list[2];
38 * next in sort order. read, write or both are NULL
40 struct request *next_rq[2];
41 unsigned int batching; /* number of sequential requests made */
42 unsigned int starved; /* times reads have starved writes */
45 * settings that change how the i/o scheduler behaves
53 static void deadline_move_request(struct deadline_data *, struct request *);
55 static inline struct rb_root *
56 deadline_rb_root(struct deadline_data *dd, struct request *rq)
58 return &dd->sort_list[rq_data_dir(rq)];
62 * get the request after `rq' in sector-sorted order
64 static inline struct request *
65 deadline_latter_request(struct request *rq)
67 struct rb_node *node = rb_next(&rq->rb_node);
70 return rb_entry_rq(node);
76 deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
78 struct rb_root *root = deadline_rb_root(dd, rq);
84 deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
86 const int data_dir = rq_data_dir(rq);
88 if (dd->next_rq[data_dir] == rq)
89 dd->next_rq[data_dir] = deadline_latter_request(rq);
91 elv_rb_del(deadline_rb_root(dd, rq), rq);
95 * add rq to rbtree and fifo
98 deadline_add_request(struct request_queue *q, struct request *rq)
100 struct deadline_data *dd = q->elevator->elevator_data;
101 const int data_dir = rq_data_dir(rq);
103 deadline_add_rq_rb(dd, rq);
106 * set expire time and add to fifo list
108 rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
109 list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
113 * remove rq from rbtree and fifo.
115 static void deadline_remove_request(struct request_queue *q, struct request *rq)
117 struct deadline_data *dd = q->elevator->elevator_data;
120 deadline_del_rq_rb(dd, rq);
123 static enum elv_merge
124 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
126 struct deadline_data *dd = q->elevator->elevator_data;
127 struct request *__rq;
130 * check for front merge
132 if (dd->front_merges) {
133 sector_t sector = bio_end_sector(bio);
135 __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
137 BUG_ON(sector != blk_rq_pos(__rq));
139 if (elv_bio_merge_ok(__rq, bio)) {
141 return ELEVATOR_FRONT_MERGE;
146 return ELEVATOR_NO_MERGE;
149 static void deadline_merged_request(struct request_queue *q,
150 struct request *req, enum elv_merge type)
152 struct deadline_data *dd = q->elevator->elevator_data;
155 * if the merge was a front merge, we need to reposition request
157 if (type == ELEVATOR_FRONT_MERGE) {
158 elv_rb_del(deadline_rb_root(dd, req), req);
159 deadline_add_rq_rb(dd, req);
164 deadline_merged_requests(struct request_queue *q, struct request *req,
165 struct request *next)
168 * if next expires before rq, assign its expire time to rq
169 * and move into next position (next will be deleted) in fifo
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;
180 * kill knowledge of next, this one is a goner
182 deadline_remove_request(q, next);
186 * move request from sort list to dispatch queue.
189 deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
191 struct request_queue *q = rq->q;
193 deadline_remove_request(q, rq);
194 elv_dispatch_add_tail(q, rq);
198 * move an entry to dispatch queue
201 deadline_move_request(struct deadline_data *dd, struct request *rq)
203 const int data_dir = rq_data_dir(rq);
205 dd->next_rq[READ] = NULL;
206 dd->next_rq[WRITE] = NULL;
207 dd->next_rq[data_dir] = deadline_latter_request(rq);
210 * take it off the sort and fifo list, move
213 deadline_move_to_dispatch(dd, rq);
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])
220 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
222 struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
227 if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
234 * deadline_dispatch_requests selects the best request according to
235 * read/write expire, fifo_batch, etc
237 static int deadline_dispatch_requests(struct request_queue *q, int force)
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]);
246 * batches are currently reads XOR writes
248 if (dd->next_rq[WRITE])
249 rq = dd->next_rq[WRITE];
251 rq = dd->next_rq[READ];
253 if (rq && dd->batching < dd->fifo_batch)
254 /* we have a next request are still entitled to batch */
255 goto dispatch_request;
258 * at this point we are not running a batch. select the appropriate
259 * data direction (read / write)
263 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
265 if (writes && (dd->starved++ >= dd->writes_starved))
266 goto dispatch_writes;
270 goto dispatch_find_request;
274 * there are either no reads or writes have been starved
279 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
285 goto dispatch_find_request;
290 dispatch_find_request:
292 * we are not running a batch, find best request for selected data_dir
294 if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
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.
300 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
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.
306 rq = dd->next_rq[data_dir];
313 * rq is the selected appropriate request.
316 deadline_move_request(dd, rq);
321 static void deadline_exit_queue(struct elevator_queue *e)
323 struct deadline_data *dd = e->elevator_data;
325 BUG_ON(!list_empty(&dd->fifo_list[READ]));
326 BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
332 * initialize elevator private data (deadline_data).
334 static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
336 struct deadline_data *dd;
337 struct elevator_queue *eq;
339 eq = elevator_alloc(q, e);
343 dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
345 kobject_put(&eq->kobj);
348 eq->elevator_data = dd;
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;
360 spin_lock_irq(q->queue_lock);
362 spin_unlock_irq(q->queue_lock);
371 deadline_var_show(int var, char *page)
373 return sprintf(page, "%d\n", var);
377 deadline_var_store(int *var, const char *page, size_t count)
379 char *p = (char *) page;
381 *var = simple_strtol(p, &p, 10);
385 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
386 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
388 struct deadline_data *dd = e->elevator_data; \
389 int __data = __VAR; \
391 __data = jiffies_to_msecs(__data); \
392 return deadline_var_show(__data, (page)); \
394 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
395 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
396 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
397 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
398 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
401 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
402 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
404 struct deadline_data *dd = e->elevator_data; \
406 int ret = deadline_var_store(&__data, (page), count); \
407 if (__data < (MIN)) \
409 else if (__data > (MAX)) \
412 *(__PTR) = msecs_to_jiffies(__data); \
417 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
418 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
419 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
420 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
421 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
422 #undef STORE_FUNCTION
424 #define DD_ATTR(name) \
425 __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
426 deadline_##name##_store)
428 static struct elv_fs_entry deadline_attrs[] = {
429 DD_ATTR(read_expire),
430 DD_ATTR(write_expire),
431 DD_ATTR(writes_starved),
432 DD_ATTR(front_merges),
437 static struct elevator_type iosched_deadline = {
439 .elevator_merge_fn = deadline_merge,
440 .elevator_merged_fn = deadline_merged_request,
441 .elevator_merge_req_fn = deadline_merged_requests,
442 .elevator_dispatch_fn = deadline_dispatch_requests,
443 .elevator_add_req_fn = deadline_add_request,
444 .elevator_former_req_fn = elv_rb_former_request,
445 .elevator_latter_req_fn = elv_rb_latter_request,
446 .elevator_init_fn = deadline_init_queue,
447 .elevator_exit_fn = deadline_exit_queue,
450 .elevator_attrs = deadline_attrs,
451 .elevator_name = "deadline",
452 .elevator_owner = THIS_MODULE,
455 static int __init deadline_init(void)
457 return elv_register(&iosched_deadline);
460 static void __exit deadline_exit(void)
462 elv_unregister(&iosched_deadline);
465 module_init(deadline_init);
466 module_exit(deadline_exit);
468 MODULE_AUTHOR("Jens Axboe");
469 MODULE_LICENSE("GPL");
470 MODULE_DESCRIPTION("deadline IO scheduler");