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Linux/block/deadline-iosched.c

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  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 inline struct rb_root *
 54 deadline_rb_root(struct deadline_data *dd, struct request *rq)
 55 {
 56         return &dd->sort_list[rq_data_dir(rq)];
 57 }
 58 
 59 /*
 60  * get the request after `rq' in sector-sorted order
 61  */
 62 static inline struct request *
 63 deadline_latter_request(struct request *rq)
 64 {
 65         struct rb_node *node = rb_next(&rq->rb_node);
 66 
 67         if (node)
 68                 return rb_entry_rq(node);
 69 
 70         return NULL;
 71 }
 72 
 73 static void
 74 deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
 75 {
 76         struct rb_root *root = deadline_rb_root(dd, rq);
 77 
 78         elv_rb_add(root, rq);
 79 }
 80 
 81 static inline void
 82 deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
 83 {
 84         const int data_dir = rq_data_dir(rq);
 85 
 86         if (dd->next_rq[data_dir] == rq)
 87                 dd->next_rq[data_dir] = deadline_latter_request(rq);
 88 
 89         elv_rb_del(deadline_rb_root(dd, rq), rq);
 90 }
 91 
 92 /*
 93  * add rq to rbtree and fifo
 94  */
 95 static void
 96 deadline_add_request(struct request_queue *q, struct request *rq)
 97 {
 98         struct deadline_data *dd = q->elevator->elevator_data;
 99         const int data_dir = rq_data_dir(rq);
100 
101         /*
102          * This may be a requeue of a write request that has locked its
103          * target zone. If it is the case, this releases the zone lock.
104          */
105         blk_req_zone_write_unlock(rq);
106 
107         deadline_add_rq_rb(dd, rq);
108 
109         /*
110          * set expire time and add to fifo list
111          */
112         rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
113         list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
114 }
115 
116 /*
117  * remove rq from rbtree and fifo.
118  */
119 static void deadline_remove_request(struct request_queue *q, struct request *rq)
120 {
121         struct deadline_data *dd = q->elevator->elevator_data;
122 
123         rq_fifo_clear(rq);
124         deadline_del_rq_rb(dd, rq);
125 }
126 
127 static enum elv_merge
128 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
129 {
130         struct deadline_data *dd = q->elevator->elevator_data;
131         struct request *__rq;
132 
133         /*
134          * check for front merge
135          */
136         if (dd->front_merges) {
137                 sector_t sector = bio_end_sector(bio);
138 
139                 __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
140                 if (__rq) {
141                         BUG_ON(sector != blk_rq_pos(__rq));
142 
143                         if (elv_bio_merge_ok(__rq, bio)) {
144                                 *req = __rq;
145                                 return ELEVATOR_FRONT_MERGE;
146                         }
147                 }
148         }
149 
150         return ELEVATOR_NO_MERGE;
151 }
152 
153 static void deadline_merged_request(struct request_queue *q,
154                                     struct request *req, enum elv_merge 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((unsigned long)next->fifo_time,
177                                 (unsigned long)req->fifo_time)) {
178                         list_move(&req->queuelist, &next->queuelist);
179                         req->fifo_time = next->fifo_time;
180                 }
181         }
182 
183         /*
184          * kill knowledge of next, this one is a goner
185          */
186         deadline_remove_request(q, next);
187 }
188 
189 /*
190  * move request from sort list to dispatch queue.
191  */
192 static inline void
193 deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
194 {
195         struct request_queue *q = rq->q;
196 
197         /*
198          * For a zoned block device, write requests must write lock their
199          * target zone.
200          */
201         blk_req_zone_write_lock(rq);
202 
203         deadline_remove_request(q, rq);
204         elv_dispatch_add_tail(q, rq);
205 }
206 
207 /*
208  * move an entry to dispatch queue
209  */
210 static void
211 deadline_move_request(struct deadline_data *dd, struct request *rq)
212 {
213         const int data_dir = rq_data_dir(rq);
214 
215         dd->next_rq[READ] = NULL;
216         dd->next_rq[WRITE] = NULL;
217         dd->next_rq[data_dir] = deadline_latter_request(rq);
218 
219         /*
220          * take it off the sort and fifo list, move
221          * to dispatch queue
222          */
223         deadline_move_to_dispatch(dd, rq);
224 }
225 
226 /*
227  * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
228  * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
229  */
230 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
231 {
232         struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
233 
234         /*
235          * rq is expired!
236          */
237         if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
238                 return 1;
239 
240         return 0;
241 }
242 
243 /*
244  * For the specified data direction, return the next request to dispatch using
245  * arrival ordered lists.
246  */
247 static struct request *
248 deadline_fifo_request(struct deadline_data *dd, int data_dir)
249 {
250         struct request *rq;
251 
252         if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
253                 return NULL;
254 
255         if (list_empty(&dd->fifo_list[data_dir]))
256                 return NULL;
257 
258         rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
259         if (data_dir == READ || !blk_queue_is_zoned(rq->q))
260                 return rq;
261 
262         /*
263          * Look for a write request that can be dispatched, that is one with
264          * an unlocked target zone.
265          */
266         list_for_each_entry(rq, &dd->fifo_list[WRITE], queuelist) {
267                 if (blk_req_can_dispatch_to_zone(rq))
268                         return rq;
269         }
270 
271         return NULL;
272 }
273 
274 /*
275  * For the specified data direction, return the next request to dispatch using
276  * sector position sorted lists.
277  */
278 static struct request *
279 deadline_next_request(struct deadline_data *dd, int data_dir)
280 {
281         struct request *rq;
282 
283         if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
284                 return NULL;
285 
286         rq = dd->next_rq[data_dir];
287         if (!rq)
288                 return NULL;
289 
290         if (data_dir == READ || !blk_queue_is_zoned(rq->q))
291                 return rq;
292 
293         /*
294          * Look for a write request that can be dispatched, that is one with
295          * an unlocked target zone.
296          */
297         while (rq) {
298                 if (blk_req_can_dispatch_to_zone(rq))
299                         return rq;
300                 rq = deadline_latter_request(rq);
301         }
302 
303         return NULL;
304 }
305 
306 /*
307  * deadline_dispatch_requests selects the best request according to
308  * read/write expire, fifo_batch, etc
309  */
310 static int deadline_dispatch_requests(struct request_queue *q, int force)
311 {
312         struct deadline_data *dd = q->elevator->elevator_data;
313         const int reads = !list_empty(&dd->fifo_list[READ]);
314         const int writes = !list_empty(&dd->fifo_list[WRITE]);
315         struct request *rq, *next_rq;
316         int data_dir;
317 
318         /*
319          * batches are currently reads XOR writes
320          */
321         rq = deadline_next_request(dd, WRITE);
322         if (!rq)
323                 rq = deadline_next_request(dd, READ);
324 
325         if (rq && dd->batching < dd->fifo_batch)
326                 /* we have a next request are still entitled to batch */
327                 goto dispatch_request;
328 
329         /*
330          * at this point we are not running a batch. select the appropriate
331          * data direction (read / write)
332          */
333 
334         if (reads) {
335                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
336 
337                 if (deadline_fifo_request(dd, WRITE) &&
338                     (dd->starved++ >= dd->writes_starved))
339                         goto dispatch_writes;
340 
341                 data_dir = READ;
342 
343                 goto dispatch_find_request;
344         }
345 
346         /*
347          * there are either no reads or writes have been starved
348          */
349 
350         if (writes) {
351 dispatch_writes:
352                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
353 
354                 dd->starved = 0;
355 
356                 data_dir = WRITE;
357 
358                 goto dispatch_find_request;
359         }
360 
361         return 0;
362 
363 dispatch_find_request:
364         /*
365          * we are not running a batch, find best request for selected data_dir
366          */
367         next_rq = deadline_next_request(dd, data_dir);
368         if (deadline_check_fifo(dd, data_dir) || !next_rq) {
369                 /*
370                  * A deadline has expired, the last request was in the other
371                  * direction, or we have run out of higher-sectored requests.
372                  * Start again from the request with the earliest expiry time.
373                  */
374                 rq = deadline_fifo_request(dd, data_dir);
375         } else {
376                 /*
377                  * The last req was the same dir and we have a next request in
378                  * sort order. No expired requests so continue on from here.
379                  */
380                 rq = next_rq;
381         }
382 
383         /*
384          * For a zoned block device, if we only have writes queued and none of
385          * them can be dispatched, rq will be NULL.
386          */
387         if (!rq)
388                 return 0;
389 
390         dd->batching = 0;
391 
392 dispatch_request:
393         /*
394          * rq is the selected appropriate request.
395          */
396         dd->batching++;
397         deadline_move_request(dd, rq);
398 
399         return 1;
400 }
401 
402 /*
403  * For zoned block devices, write unlock the target zone of completed
404  * write requests.
405  */
406 static void
407 deadline_completed_request(struct request_queue *q, struct request *rq)
408 {
409         blk_req_zone_write_unlock(rq);
410 }
411 
412 static void deadline_exit_queue(struct elevator_queue *e)
413 {
414         struct deadline_data *dd = e->elevator_data;
415 
416         BUG_ON(!list_empty(&dd->fifo_list[READ]));
417         BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
418 
419         kfree(dd);
420 }
421 
422 /*
423  * initialize elevator private data (deadline_data).
424  */
425 static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
426 {
427         struct deadline_data *dd;
428         struct elevator_queue *eq;
429 
430         eq = elevator_alloc(q, e);
431         if (!eq)
432                 return -ENOMEM;
433 
434         dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
435         if (!dd) {
436                 kobject_put(&eq->kobj);
437                 return -ENOMEM;
438         }
439         eq->elevator_data = dd;
440 
441         INIT_LIST_HEAD(&dd->fifo_list[READ]);
442         INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
443         dd->sort_list[READ] = RB_ROOT;
444         dd->sort_list[WRITE] = RB_ROOT;
445         dd->fifo_expire[READ] = read_expire;
446         dd->fifo_expire[WRITE] = write_expire;
447         dd->writes_starved = writes_starved;
448         dd->front_merges = 1;
449         dd->fifo_batch = fifo_batch;
450 
451         spin_lock_irq(q->queue_lock);
452         q->elevator = eq;
453         spin_unlock_irq(q->queue_lock);
454         return 0;
455 }
456 
457 /*
458  * sysfs parts below
459  */
460 
461 static ssize_t
462 deadline_var_show(int var, char *page)
463 {
464         return sprintf(page, "%d\n", var);
465 }
466 
467 static void
468 deadline_var_store(int *var, const char *page)
469 {
470         char *p = (char *) page;
471 
472         *var = simple_strtol(p, &p, 10);
473 }
474 
475 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
476 static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
477 {                                                                       \
478         struct deadline_data *dd = e->elevator_data;                    \
479         int __data = __VAR;                                             \
480         if (__CONV)                                                     \
481                 __data = jiffies_to_msecs(__data);                      \
482         return deadline_var_show(__data, (page));                       \
483 }
484 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
485 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
486 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
487 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
488 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
489 #undef SHOW_FUNCTION
490 
491 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
492 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
493 {                                                                       \
494         struct deadline_data *dd = e->elevator_data;                    \
495         int __data;                                                     \
496         deadline_var_store(&__data, (page));                            \
497         if (__data < (MIN))                                             \
498                 __data = (MIN);                                         \
499         else if (__data > (MAX))                                        \
500                 __data = (MAX);                                         \
501         if (__CONV)                                                     \
502                 *(__PTR) = msecs_to_jiffies(__data);                    \
503         else                                                            \
504                 *(__PTR) = __data;                                      \
505         return count;                                                   \
506 }
507 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
508 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
509 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
510 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
511 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
512 #undef STORE_FUNCTION
513 
514 #define DD_ATTR(name) \
515         __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
516                                       deadline_##name##_store)
517 
518 static struct elv_fs_entry deadline_attrs[] = {
519         DD_ATTR(read_expire),
520         DD_ATTR(write_expire),
521         DD_ATTR(writes_starved),
522         DD_ATTR(front_merges),
523         DD_ATTR(fifo_batch),
524         __ATTR_NULL
525 };
526 
527 static struct elevator_type iosched_deadline = {
528         .ops.sq = {
529                 .elevator_merge_fn =            deadline_merge,
530                 .elevator_merged_fn =           deadline_merged_request,
531                 .elevator_merge_req_fn =        deadline_merged_requests,
532                 .elevator_dispatch_fn =         deadline_dispatch_requests,
533                 .elevator_completed_req_fn =    deadline_completed_request,
534                 .elevator_add_req_fn =          deadline_add_request,
535                 .elevator_former_req_fn =       elv_rb_former_request,
536                 .elevator_latter_req_fn =       elv_rb_latter_request,
537                 .elevator_init_fn =             deadline_init_queue,
538                 .elevator_exit_fn =             deadline_exit_queue,
539         },
540 
541         .elevator_attrs = deadline_attrs,
542         .elevator_name = "deadline",
543         .elevator_owner = THIS_MODULE,
544 };
545 
546 static int __init deadline_init(void)
547 {
548         return elv_register(&iosched_deadline);
549 }
550 
551 static void __exit deadline_exit(void)
552 {
553         elv_unregister(&iosched_deadline);
554 }
555 
556 module_init(deadline_init);
557 module_exit(deadline_exit);
558 
559 MODULE_AUTHOR("Jens Axboe");
560 MODULE_LICENSE("GPL");
561 MODULE_DESCRIPTION("deadline IO scheduler");
562 

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