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 sector_t last_sector; /* head position */
43 unsigned int starved; /* times reads have starved writes */
46 * settings that change how the i/o scheduler behaves
54 static void deadline_move_request(struct deadline_data *, struct request *);
56 static inline struct rb_root *
57 deadline_rb_root(struct deadline_data *dd, struct request *rq)
59 return &dd->sort_list[rq_data_dir(rq)];
63 * get the request after `rq' in sector-sorted order
65 static inline struct request *
66 deadline_latter_request(struct request *rq)
68 struct rb_node *node = rb_next(&rq->rb_node);
71 return rb_entry_rq(node);
77 deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
79 struct rb_root *root = deadline_rb_root(dd, rq);
85 deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
87 const int data_dir = rq_data_dir(rq);
89 if (dd->next_rq[data_dir] == rq)
90 dd->next_rq[data_dir] = deadline_latter_request(rq);
92 elv_rb_del(deadline_rb_root(dd, rq), rq);
96 * add rq to rbtree and fifo
99 deadline_add_request(struct request_queue *q, struct request *rq)
101 struct deadline_data *dd = q->elevator->elevator_data;
102 const int data_dir = rq_data_dir(rq);
104 deadline_add_rq_rb(dd, rq);
107 * set expire time and add to fifo list
109 rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
110 list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
114 * remove rq from rbtree and fifo.
116 static void deadline_remove_request(struct request_queue *q, struct request *rq)
118 struct deadline_data *dd = q->elevator->elevator_data;
121 deadline_del_rq_rb(dd, rq);
125 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
127 struct deadline_data *dd = q->elevator->elevator_data;
128 struct request *__rq;
132 * check for front merge
134 if (dd->front_merges) {
135 sector_t sector = bio_end_sector(bio);
137 __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
139 BUG_ON(sector != blk_rq_pos(__rq));
141 if (elv_rq_merge_ok(__rq, bio)) {
142 ret = ELEVATOR_FRONT_MERGE;
148 return ELEVATOR_NO_MERGE;
154 static void deadline_merged_request(struct request_queue *q,
155 struct request *req, int type)
157 struct deadline_data *dd = q->elevator->elevator_data;
160 * if the merge was a front merge, we need to reposition request
162 if (type == ELEVATOR_FRONT_MERGE) {
163 elv_rb_del(deadline_rb_root(dd, req), req);
164 deadline_add_rq_rb(dd, req);
169 deadline_merged_requests(struct request_queue *q, struct request *req,
170 struct request *next)
173 * if next expires before rq, assign its expire time to rq
174 * and move into next position (next will be deleted) in fifo
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;
184 * kill knowledge of next, this one is a goner
186 deadline_remove_request(q, next);
190 * move request from sort list to dispatch queue.
193 deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
195 struct request_queue *q = rq->q;
197 deadline_remove_request(q, rq);
198 elv_dispatch_add_tail(q, rq);
202 * move an entry to dispatch queue
205 deadline_move_request(struct deadline_data *dd, struct request *rq)
207 const int data_dir = rq_data_dir(rq);
209 dd->next_rq[READ] = NULL;
210 dd->next_rq[WRITE] = NULL;
211 dd->next_rq[data_dir] = deadline_latter_request(rq);
213 dd->last_sector = rq_end_sector(rq);
216 * take it off the sort and fifo list, move
219 deadline_move_to_dispatch(dd, rq);
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])
226 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
228 struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
233 if (time_after_eq(jiffies, rq->fifo_time))
240 * deadline_dispatch_requests selects the best request according to
241 * read/write expire, fifo_batch, etc
243 static int deadline_dispatch_requests(struct request_queue *q, int force)
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]);
252 * batches are currently reads XOR writes
254 if (dd->next_rq[WRITE])
255 rq = dd->next_rq[WRITE];
257 rq = dd->next_rq[READ];
259 if (rq && dd->batching < dd->fifo_batch)
260 /* we have a next request are still entitled to batch */
261 goto dispatch_request;
264 * at this point we are not running a batch. select the appropriate
265 * data direction (read / write)
269 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
271 if (writes && (dd->starved++ >= dd->writes_starved))
272 goto dispatch_writes;
276 goto dispatch_find_request;
280 * there are either no reads or writes have been starved
285 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
291 goto dispatch_find_request;
296 dispatch_find_request:
298 * we are not running a batch, find best request for selected data_dir
300 if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
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.
306 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
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.
312 rq = dd->next_rq[data_dir];
319 * rq is the selected appropriate request.
322 deadline_move_request(dd, rq);
327 static void deadline_exit_queue(struct elevator_queue *e)
329 struct deadline_data *dd = e->elevator_data;
331 BUG_ON(!list_empty(&dd->fifo_list[READ]));
332 BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
338 * initialize elevator private data (deadline_data).
340 static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
342 struct deadline_data *dd;
343 struct elevator_queue *eq;
345 eq = elevator_alloc(q, e);
349 dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
351 kobject_put(&eq->kobj);
354 eq->elevator_data = dd;
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;
366 spin_lock_irq(q->queue_lock);
368 spin_unlock_irq(q->queue_lock);
377 deadline_var_show(int var, char *page)
379 return sprintf(page, "%d\n", var);
383 deadline_var_store(int *var, const char *page, size_t count)
385 char *p = (char *) page;
387 *var = simple_strtol(p, &p, 10);
391 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
392 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
394 struct deadline_data *dd = e->elevator_data; \
395 int __data = __VAR; \
397 __data = jiffies_to_msecs(__data); \
398 return deadline_var_show(__data, (page)); \
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);
407 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
408 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
410 struct deadline_data *dd = e->elevator_data; \
412 int ret = deadline_var_store(&__data, (page), count); \
413 if (__data < (MIN)) \
415 else if (__data > (MAX)) \
418 *(__PTR) = msecs_to_jiffies(__data); \
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
430 #define DD_ATTR(name) \
431 __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
432 deadline_##name##_store)
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),
443 static struct elevator_type iosched_deadline = {
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,
456 .elevator_attrs = deadline_attrs,
457 .elevator_name = "deadline",
458 .elevator_owner = THIS_MODULE,
461 static int __init deadline_init(void)
463 return elv_register(&iosched_deadline);
466 static void __exit deadline_exit(void)
468 elv_unregister(&iosched_deadline);
471 module_init(deadline_init);
472 module_exit(deadline_exit);
474 MODULE_AUTHOR("Jens Axboe");
475 MODULE_LICENSE("GPL");
476 MODULE_DESCRIPTION("deadline IO scheduler");