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

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