[SG] Get rid of __sg_mark_end()
[linux-2.6.git] / block / deadline-iosched.c
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         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;
52 };
53
54 static void deadline_move_request(struct deadline_data *, struct request *);
55
56 #define RQ_RB_ROOT(dd, rq)      (&(dd)->sort_list[rq_data_dir((rq))])
57
58 static void
59 deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
60 {
61         struct rb_root *root = RQ_RB_ROOT(dd, rq);
62         struct request *__alias;
63
64 retry:
65         __alias = elv_rb_add(root, rq);
66         if (unlikely(__alias)) {
67                 deadline_move_request(dd, __alias);
68                 goto retry;
69         }
70 }
71
72 static inline void
73 deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
74 {
75         const int data_dir = rq_data_dir(rq);
76
77         if (dd->next_rq[data_dir] == rq) {
78                 struct rb_node *rbnext = rb_next(&rq->rb_node);
79
80                 dd->next_rq[data_dir] = NULL;
81                 if (rbnext)
82                         dd->next_rq[data_dir] = rb_entry_rq(rbnext);
83         }
84
85         elv_rb_del(RQ_RB_ROOT(dd, rq), rq);
86 }
87
88 /*
89  * add rq to rbtree and fifo
90  */
91 static void
92 deadline_add_request(struct request_queue *q, struct request *rq)
93 {
94         struct deadline_data *dd = q->elevator->elevator_data;
95         const int data_dir = rq_data_dir(rq);
96
97         deadline_add_rq_rb(dd, rq);
98
99         /*
100          * set expire time (only used for reads) and add to fifo list
101          */
102         rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
103         list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
104 }
105
106 /*
107  * remove rq from rbtree and fifo.
108  */
109 static void deadline_remove_request(struct request_queue *q, struct request *rq)
110 {
111         struct deadline_data *dd = q->elevator->elevator_data;
112
113         rq_fifo_clear(rq);
114         deadline_del_rq_rb(dd, rq);
115 }
116
117 static int
118 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
119 {
120         struct deadline_data *dd = q->elevator->elevator_data;
121         struct request *__rq;
122         int ret;
123
124         /*
125          * check for front merge
126          */
127         if (dd->front_merges) {
128                 sector_t sector = bio->bi_sector + bio_sectors(bio);
129
130                 __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
131                 if (__rq) {
132                         BUG_ON(sector != __rq->sector);
133
134                         if (elv_rq_merge_ok(__rq, bio)) {
135                                 ret = ELEVATOR_FRONT_MERGE;
136                                 goto out;
137                         }
138                 }
139         }
140
141         return ELEVATOR_NO_MERGE;
142 out:
143         *req = __rq;
144         return ret;
145 }
146
147 static void deadline_merged_request(struct request_queue *q,
148                                     struct request *req, int type)
149 {
150         struct deadline_data *dd = q->elevator->elevator_data;
151
152         /*
153          * if the merge was a front merge, we need to reposition request
154          */
155         if (type == ELEVATOR_FRONT_MERGE) {
156                 elv_rb_del(RQ_RB_ROOT(dd, req), req);
157                 deadline_add_rq_rb(dd, req);
158         }
159 }
160
161 static void
162 deadline_merged_requests(struct request_queue *q, struct request *req,
163                          struct request *next)
164 {
165         /*
166          * if next expires before rq, assign its expire time to rq
167          * and move into next position (next will be deleted) in fifo
168          */
169         if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
170                 if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
171                         list_move(&req->queuelist, &next->queuelist);
172                         rq_set_fifo_time(req, rq_fifo_time(next));
173                 }
174         }
175
176         /*
177          * kill knowledge of next, this one is a goner
178          */
179         deadline_remove_request(q, next);
180 }
181
182 /*
183  * move request from sort list to dispatch queue.
184  */
185 static inline void
186 deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
187 {
188         struct request_queue *q = rq->q;
189
190         deadline_remove_request(q, rq);
191         elv_dispatch_add_tail(q, rq);
192 }
193
194 /*
195  * move an entry to dispatch queue
196  */
197 static void
198 deadline_move_request(struct deadline_data *dd, struct request *rq)
199 {
200         const int data_dir = rq_data_dir(rq);
201         struct rb_node *rbnext = rb_next(&rq->rb_node);
202
203         dd->next_rq[READ] = NULL;
204         dd->next_rq[WRITE] = NULL;
205
206         if (rbnext)
207                 dd->next_rq[data_dir] = rb_entry_rq(rbnext);
208         
209         dd->last_sector = rq->sector + rq->nr_sectors;
210
211         /*
212          * take it off the sort and fifo list, move
213          * to dispatch queue
214          */
215         deadline_move_to_dispatch(dd, rq);
216 }
217
218 /*
219  * deadline_check_fifo returns 0 if there are no expired reads on the fifo,
220  * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
221  */
222 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
223 {
224         struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
225
226         /*
227          * rq is expired!
228          */
229         if (time_after(jiffies, rq_fifo_time(rq)))
230                 return 1;
231
232         return 0;
233 }
234
235 /*
236  * deadline_dispatch_requests selects the best request according to
237  * read/write expire, fifo_batch, etc
238  */
239 static int deadline_dispatch_requests(struct request_queue *q, int force)
240 {
241         struct deadline_data *dd = q->elevator->elevator_data;
242         const int reads = !list_empty(&dd->fifo_list[READ]);
243         const int writes = !list_empty(&dd->fifo_list[WRITE]);
244         struct request *rq;
245         int data_dir;
246
247         /*
248          * batches are currently reads XOR writes
249          */
250         if (dd->next_rq[WRITE])
251                 rq = dd->next_rq[WRITE];
252         else
253                 rq = dd->next_rq[READ];
254
255         if (rq) {
256                 /* we have a "next request" */
257                 
258                 if (dd->last_sector != rq->sector)
259                         /* end the batch on a non sequential request */
260                         dd->batching += dd->fifo_batch;
261                 
262                 if (dd->batching < dd->fifo_batch)
263                         /* we are still entitled to batch */
264                         goto dispatch_request;
265         }
266
267         /*
268          * at this point we are not running a batch. select the appropriate
269          * data direction (read / write)
270          */
271
272         if (reads) {
273                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
274
275                 if (writes && (dd->starved++ >= dd->writes_starved))
276                         goto dispatch_writes;
277
278                 data_dir = READ;
279
280                 goto dispatch_find_request;
281         }
282
283         /*
284          * there are either no reads or writes have been starved
285          */
286
287         if (writes) {
288 dispatch_writes:
289                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
290
291                 dd->starved = 0;
292
293                 data_dir = WRITE;
294
295                 goto dispatch_find_request;
296         }
297
298         return 0;
299
300 dispatch_find_request:
301         /*
302          * we are not running a batch, find best request for selected data_dir
303          */
304         if (deadline_check_fifo(dd, data_dir)) {
305                 /* An expired request exists - satisfy it */
306                 dd->batching = 0;
307                 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
308                 
309         } else if (dd->next_rq[data_dir]) {
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                  */
314                 rq = dd->next_rq[data_dir];
315         } else {
316                 struct rb_node *node;
317                 /*
318                  * The last req was the other direction or we have run out of
319                  * higher-sectored requests. Go back to the lowest sectored
320                  * request (1 way elevator) and start a new batch.
321                  */
322                 dd->batching = 0;
323                 node = rb_first(&dd->sort_list[data_dir]);
324                 if (node)
325                         rq = rb_entry_rq(node);
326         }
327
328 dispatch_request:
329         /*
330          * rq is the selected appropriate request.
331          */
332         dd->batching++;
333         deadline_move_request(dd, rq);
334
335         return 1;
336 }
337
338 static int deadline_queue_empty(struct request_queue *q)
339 {
340         struct deadline_data *dd = q->elevator->elevator_data;
341
342         return list_empty(&dd->fifo_list[WRITE])
343                 && list_empty(&dd->fifo_list[READ]);
344 }
345
346 static void deadline_exit_queue(elevator_t *e)
347 {
348         struct deadline_data *dd = e->elevator_data;
349
350         BUG_ON(!list_empty(&dd->fifo_list[READ]));
351         BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
352
353         kfree(dd);
354 }
355
356 /*
357  * initialize elevator private data (deadline_data).
358  */
359 static void *deadline_init_queue(struct request_queue *q)
360 {
361         struct deadline_data *dd;
362
363         dd = kmalloc_node(sizeof(*dd), GFP_KERNEL | __GFP_ZERO, q->node);
364         if (!dd)
365                 return NULL;
366
367         INIT_LIST_HEAD(&dd->fifo_list[READ]);
368         INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
369         dd->sort_list[READ] = RB_ROOT;
370         dd->sort_list[WRITE] = RB_ROOT;
371         dd->fifo_expire[READ] = read_expire;
372         dd->fifo_expire[WRITE] = write_expire;
373         dd->writes_starved = writes_starved;
374         dd->front_merges = 1;
375         dd->fifo_batch = fifo_batch;
376         return dd;
377 }
378
379 /*
380  * sysfs parts below
381  */
382
383 static ssize_t
384 deadline_var_show(int var, char *page)
385 {
386         return sprintf(page, "%d\n", var);
387 }
388
389 static ssize_t
390 deadline_var_store(int *var, const char *page, size_t count)
391 {
392         char *p = (char *) page;
393
394         *var = simple_strtol(p, &p, 10);
395         return count;
396 }
397
398 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
399 static ssize_t __FUNC(elevator_t *e, char *page)                        \
400 {                                                                       \
401         struct deadline_data *dd = e->elevator_data;                    \
402         int __data = __VAR;                                             \
403         if (__CONV)                                                     \
404                 __data = jiffies_to_msecs(__data);                      \
405         return deadline_var_show(__data, (page));                       \
406 }
407 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
408 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
409 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
410 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
411 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
412 #undef SHOW_FUNCTION
413
414 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
415 static ssize_t __FUNC(elevator_t *e, const char *page, size_t count)    \
416 {                                                                       \
417         struct deadline_data *dd = e->elevator_data;                    \
418         int __data;                                                     \
419         int ret = deadline_var_store(&__data, (page), count);           \
420         if (__data < (MIN))                                             \
421                 __data = (MIN);                                         \
422         else if (__data > (MAX))                                        \
423                 __data = (MAX);                                         \
424         if (__CONV)                                                     \
425                 *(__PTR) = msecs_to_jiffies(__data);                    \
426         else                                                            \
427                 *(__PTR) = __data;                                      \
428         return ret;                                                     \
429 }
430 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
431 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
432 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
433 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
434 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
435 #undef STORE_FUNCTION
436
437 #define DD_ATTR(name) \
438         __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
439                                       deadline_##name##_store)
440
441 static struct elv_fs_entry deadline_attrs[] = {
442         DD_ATTR(read_expire),
443         DD_ATTR(write_expire),
444         DD_ATTR(writes_starved),
445         DD_ATTR(front_merges),
446         DD_ATTR(fifo_batch),
447         __ATTR_NULL
448 };
449
450 static struct elevator_type iosched_deadline = {
451         .ops = {
452                 .elevator_merge_fn =            deadline_merge,
453                 .elevator_merged_fn =           deadline_merged_request,
454                 .elevator_merge_req_fn =        deadline_merged_requests,
455                 .elevator_dispatch_fn =         deadline_dispatch_requests,
456                 .elevator_add_req_fn =          deadline_add_request,
457                 .elevator_queue_empty_fn =      deadline_queue_empty,
458                 .elevator_former_req_fn =       elv_rb_former_request,
459                 .elevator_latter_req_fn =       elv_rb_latter_request,
460                 .elevator_init_fn =             deadline_init_queue,
461                 .elevator_exit_fn =             deadline_exit_queue,
462         },
463
464         .elevator_attrs = deadline_attrs,
465         .elevator_name = "deadline",
466         .elevator_owner = THIS_MODULE,
467 };
468
469 static int __init deadline_init(void)
470 {
471         return elv_register(&iosched_deadline);
472 }
473
474 static void __exit deadline_exit(void)
475 {
476         elv_unregister(&iosched_deadline);
477 }
478
479 module_init(deadline_init);
480 module_exit(deadline_exit);
481
482 MODULE_AUTHOR("Jens Axboe");
483 MODULE_LICENSE("GPL");
484 MODULE_DESCRIPTION("deadline IO scheduler");