1 /*
2 * Hierarchical Budget Worst-case Fair Weighted Fair Queueing
3 * (B-WF2Q+): hierarchical scheduling algorithm by which the BFQ I/O
4 * scheduler schedules generic entities. The latter can represent
5 * either single bfq queues (associated with processes) or groups of
6 * bfq queues (associated with cgroups).
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2 of the
11 * License, or (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * General Public License for more details.
17 */
18 #include "bfq-iosched.h"
19
20 /**
21 * bfq_gt - compare two timestamps.
22 * @a: first ts.
23 * @b: second ts.
24 *
25 * Return @a > @b, dealing with wrapping correctly.
26 */
bfq_gt(u64 a,u64 b)27 static int bfq_gt(u64 a, u64 b)
28 {
29 return (s64)(a - b) > 0;
30 }
31
bfq_root_active_entity(struct rb_root * tree)32 static struct bfq_entity *bfq_root_active_entity(struct rb_root *tree)
33 {
34 struct rb_node *node = tree->rb_node;
35
36 return rb_entry(node, struct bfq_entity, rb_node);
37 }
38
bfq_class_idx(struct bfq_entity * entity)39 static unsigned int bfq_class_idx(struct bfq_entity *entity)
40 {
41 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
42
43 return bfqq ? bfqq->ioprio_class - 1 :
44 BFQ_DEFAULT_GRP_CLASS - 1;
45 }
46
47 static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
48 bool expiration);
49
50 static bool bfq_update_parent_budget(struct bfq_entity *next_in_service);
51
52 /**
53 * bfq_update_next_in_service - update sd->next_in_service
54 * @sd: sched_data for which to perform the update.
55 * @new_entity: if not NULL, pointer to the entity whose activation,
56 * requeueing or repositionig triggered the invocation of
57 * this function.
58 * @expiration: id true, this function is being invoked after the
59 * expiration of the in-service entity
60 *
61 * This function is called to update sd->next_in_service, which, in
62 * its turn, may change as a consequence of the insertion or
63 * extraction of an entity into/from one of the active trees of
64 * sd. These insertions/extractions occur as a consequence of
65 * activations/deactivations of entities, with some activations being
66 * 'true' activations, and other activations being requeueings (i.e.,
67 * implementing the second, requeueing phase of the mechanism used to
68 * reposition an entity in its active tree; see comments on
69 * __bfq_activate_entity and __bfq_requeue_entity for details). In
70 * both the last two activation sub-cases, new_entity points to the
71 * just activated or requeued entity.
72 *
73 * Returns true if sd->next_in_service changes in such a way that
74 * entity->parent may become the next_in_service for its parent
75 * entity.
76 */
bfq_update_next_in_service(struct bfq_sched_data * sd,struct bfq_entity * new_entity,bool expiration)77 static bool bfq_update_next_in_service(struct bfq_sched_data *sd,
78 struct bfq_entity *new_entity,
79 bool expiration)
80 {
81 struct bfq_entity *next_in_service = sd->next_in_service;
82 bool parent_sched_may_change = false;
83 bool change_without_lookup = false;
84
85 /*
86 * If this update is triggered by the activation, requeueing
87 * or repositiong of an entity that does not coincide with
88 * sd->next_in_service, then a full lookup in the active tree
89 * can be avoided. In fact, it is enough to check whether the
90 * just-modified entity has the same priority as
91 * sd->next_in_service, is eligible and has a lower virtual
92 * finish time than sd->next_in_service. If this compound
93 * condition holds, then the new entity becomes the new
94 * next_in_service. Otherwise no change is needed.
95 */
96 if (new_entity && new_entity != sd->next_in_service) {
97 /*
98 * Flag used to decide whether to replace
99 * sd->next_in_service with new_entity. Tentatively
100 * set to true, and left as true if
101 * sd->next_in_service is NULL.
102 */
103 change_without_lookup = true;
104
105 /*
106 * If there is already a next_in_service candidate
107 * entity, then compare timestamps to decide whether
108 * to replace sd->service_tree with new_entity.
109 */
110 if (next_in_service) {
111 unsigned int new_entity_class_idx =
112 bfq_class_idx(new_entity);
113 struct bfq_service_tree *st =
114 sd->service_tree + new_entity_class_idx;
115
116 change_without_lookup =
117 (new_entity_class_idx ==
118 bfq_class_idx(next_in_service)
119 &&
120 !bfq_gt(new_entity->start, st->vtime)
121 &&
122 bfq_gt(next_in_service->finish,
123 new_entity->finish));
124 }
125
126 if (change_without_lookup)
127 next_in_service = new_entity;
128 }
129
130 if (!change_without_lookup) /* lookup needed */
131 next_in_service = bfq_lookup_next_entity(sd, expiration);
132
133 if (next_in_service) {
134 bool new_budget_triggers_change =
135 bfq_update_parent_budget(next_in_service);
136
137 parent_sched_may_change = !sd->next_in_service ||
138 new_budget_triggers_change;
139 }
140
141 sd->next_in_service = next_in_service;
142
143 if (!next_in_service)
144 return parent_sched_may_change;
145
146 return parent_sched_may_change;
147 }
148
149 #ifdef CONFIG_BFQ_GROUP_IOSCHED
150
bfq_bfqq_to_bfqg(struct bfq_queue * bfqq)151 struct bfq_group *bfq_bfqq_to_bfqg(struct bfq_queue *bfqq)
152 {
153 struct bfq_entity *group_entity = bfqq->entity.parent;
154
155 if (!group_entity)
156 group_entity = &bfqq->bfqd->root_group->entity;
157
158 return container_of(group_entity, struct bfq_group, entity);
159 }
160
161 /*
162 * Returns true if this budget changes may let next_in_service->parent
163 * become the next_in_service entity for its parent entity.
164 */
bfq_update_parent_budget(struct bfq_entity * next_in_service)165 static bool bfq_update_parent_budget(struct bfq_entity *next_in_service)
166 {
167 struct bfq_entity *bfqg_entity;
168 struct bfq_group *bfqg;
169 struct bfq_sched_data *group_sd;
170 bool ret = false;
171
172 group_sd = next_in_service->sched_data;
173
174 bfqg = container_of(group_sd, struct bfq_group, sched_data);
175 /*
176 * bfq_group's my_entity field is not NULL only if the group
177 * is not the root group. We must not touch the root entity
178 * as it must never become an in-service entity.
179 */
180 bfqg_entity = bfqg->my_entity;
181 if (bfqg_entity) {
182 if (bfqg_entity->budget > next_in_service->budget)
183 ret = true;
184 bfqg_entity->budget = next_in_service->budget;
185 }
186
187 return ret;
188 }
189
190 /*
191 * This function tells whether entity stops being a candidate for next
192 * service, according to the restrictive definition of the field
193 * next_in_service. In particular, this function is invoked for an
194 * entity that is about to be set in service.
195 *
196 * If entity is a queue, then the entity is no longer a candidate for
197 * next service according to the that definition, because entity is
198 * about to become the in-service queue. This function then returns
199 * true if entity is a queue.
200 *
201 * In contrast, entity could still be a candidate for next service if
202 * it is not a queue, and has more than one active child. In fact,
203 * even if one of its children is about to be set in service, other
204 * active children may still be the next to serve, for the parent
205 * entity, even according to the above definition. As a consequence, a
206 * non-queue entity is not a candidate for next-service only if it has
207 * only one active child. And only if this condition holds, then this
208 * function returns true for a non-queue entity.
209 */
bfq_no_longer_next_in_service(struct bfq_entity * entity)210 static bool bfq_no_longer_next_in_service(struct bfq_entity *entity)
211 {
212 struct bfq_group *bfqg;
213
214 if (bfq_entity_to_bfqq(entity))
215 return true;
216
217 bfqg = container_of(entity, struct bfq_group, entity);
218
219 /*
220 * The field active_entities does not always contain the
221 * actual number of active children entities: it happens to
222 * not account for the in-service entity in case the latter is
223 * removed from its active tree (which may get done after
224 * invoking the function bfq_no_longer_next_in_service in
225 * bfq_get_next_queue). Fortunately, here, i.e., while
226 * bfq_no_longer_next_in_service is not yet completed in
227 * bfq_get_next_queue, bfq_active_extract has not yet been
228 * invoked, and thus active_entities still coincides with the
229 * actual number of active entities.
230 */
231 if (bfqg->active_entities == 1)
232 return true;
233
234 return false;
235 }
236
237 #else /* CONFIG_BFQ_GROUP_IOSCHED */
238
bfq_bfqq_to_bfqg(struct bfq_queue * bfqq)239 struct bfq_group *bfq_bfqq_to_bfqg(struct bfq_queue *bfqq)
240 {
241 return bfqq->bfqd->root_group;
242 }
243
bfq_update_parent_budget(struct bfq_entity * next_in_service)244 static bool bfq_update_parent_budget(struct bfq_entity *next_in_service)
245 {
246 return false;
247 }
248
bfq_no_longer_next_in_service(struct bfq_entity * entity)249 static bool bfq_no_longer_next_in_service(struct bfq_entity *entity)
250 {
251 return true;
252 }
253
254 #endif /* CONFIG_BFQ_GROUP_IOSCHED */
255
256 /*
257 * Shift for timestamp calculations. This actually limits the maximum
258 * service allowed in one timestamp delta (small shift values increase it),
259 * the maximum total weight that can be used for the queues in the system
260 * (big shift values increase it), and the period of virtual time
261 * wraparounds.
262 */
263 #define WFQ_SERVICE_SHIFT 22
264
bfq_entity_to_bfqq(struct bfq_entity * entity)265 struct bfq_queue *bfq_entity_to_bfqq(struct bfq_entity *entity)
266 {
267 struct bfq_queue *bfqq = NULL;
268
269 if (!entity->my_sched_data)
270 bfqq = container_of(entity, struct bfq_queue, entity);
271
272 return bfqq;
273 }
274
275
276 /**
277 * bfq_delta - map service into the virtual time domain.
278 * @service: amount of service.
279 * @weight: scale factor (weight of an entity or weight sum).
280 */
bfq_delta(unsigned long service,unsigned long weight)281 static u64 bfq_delta(unsigned long service, unsigned long weight)
282 {
283 u64 d = (u64)service << WFQ_SERVICE_SHIFT;
284
285 do_div(d, weight);
286 return d;
287 }
288
289 /**
290 * bfq_calc_finish - assign the finish time to an entity.
291 * @entity: the entity to act upon.
292 * @service: the service to be charged to the entity.
293 */
bfq_calc_finish(struct bfq_entity * entity,unsigned long service)294 static void bfq_calc_finish(struct bfq_entity *entity, unsigned long service)
295 {
296 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
297
298 entity->finish = entity->start +
299 bfq_delta(service, entity->weight);
300
301 if (bfqq) {
302 bfq_log_bfqq(bfqq->bfqd, bfqq,
303 "calc_finish: serv %lu, w %d",
304 service, entity->weight);
305 bfq_log_bfqq(bfqq->bfqd, bfqq,
306 "calc_finish: start %llu, finish %llu, delta %llu",
307 entity->start, entity->finish,
308 bfq_delta(service, entity->weight));
309 }
310 }
311
312 /**
313 * bfq_entity_of - get an entity from a node.
314 * @node: the node field of the entity.
315 *
316 * Convert a node pointer to the relative entity. This is used only
317 * to simplify the logic of some functions and not as the generic
318 * conversion mechanism because, e.g., in the tree walking functions,
319 * the check for a %NULL value would be redundant.
320 */
bfq_entity_of(struct rb_node * node)321 struct bfq_entity *bfq_entity_of(struct rb_node *node)
322 {
323 struct bfq_entity *entity = NULL;
324
325 if (node)
326 entity = rb_entry(node, struct bfq_entity, rb_node);
327
328 return entity;
329 }
330
331 /**
332 * bfq_extract - remove an entity from a tree.
333 * @root: the tree root.
334 * @entity: the entity to remove.
335 */
bfq_extract(struct rb_root * root,struct bfq_entity * entity)336 static void bfq_extract(struct rb_root *root, struct bfq_entity *entity)
337 {
338 entity->tree = NULL;
339 rb_erase(&entity->rb_node, root);
340 }
341
342 /**
343 * bfq_idle_extract - extract an entity from the idle tree.
344 * @st: the service tree of the owning @entity.
345 * @entity: the entity being removed.
346 */
bfq_idle_extract(struct bfq_service_tree * st,struct bfq_entity * entity)347 static void bfq_idle_extract(struct bfq_service_tree *st,
348 struct bfq_entity *entity)
349 {
350 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
351 struct rb_node *next;
352
353 if (entity == st->first_idle) {
354 next = rb_next(&entity->rb_node);
355 st->first_idle = bfq_entity_of(next);
356 }
357
358 if (entity == st->last_idle) {
359 next = rb_prev(&entity->rb_node);
360 st->last_idle = bfq_entity_of(next);
361 }
362
363 bfq_extract(&st->idle, entity);
364
365 if (bfqq)
366 list_del(&bfqq->bfqq_list);
367 }
368
369 /**
370 * bfq_insert - generic tree insertion.
371 * @root: tree root.
372 * @entity: entity to insert.
373 *
374 * This is used for the idle and the active tree, since they are both
375 * ordered by finish time.
376 */
bfq_insert(struct rb_root * root,struct bfq_entity * entity)377 static void bfq_insert(struct rb_root *root, struct bfq_entity *entity)
378 {
379 struct bfq_entity *entry;
380 struct rb_node **node = &root->rb_node;
381 struct rb_node *parent = NULL;
382
383 while (*node) {
384 parent = *node;
385 entry = rb_entry(parent, struct bfq_entity, rb_node);
386
387 if (bfq_gt(entry->finish, entity->finish))
388 node = &parent->rb_left;
389 else
390 node = &parent->rb_right;
391 }
392
393 rb_link_node(&entity->rb_node, parent, node);
394 rb_insert_color(&entity->rb_node, root);
395
396 entity->tree = root;
397 }
398
399 /**
400 * bfq_update_min - update the min_start field of a entity.
401 * @entity: the entity to update.
402 * @node: one of its children.
403 *
404 * This function is called when @entity may store an invalid value for
405 * min_start due to updates to the active tree. The function assumes
406 * that the subtree rooted at @node (which may be its left or its right
407 * child) has a valid min_start value.
408 */
bfq_update_min(struct bfq_entity * entity,struct rb_node * node)409 static void bfq_update_min(struct bfq_entity *entity, struct rb_node *node)
410 {
411 struct bfq_entity *child;
412
413 if (node) {
414 child = rb_entry(node, struct bfq_entity, rb_node);
415 if (bfq_gt(entity->min_start, child->min_start))
416 entity->min_start = child->min_start;
417 }
418 }
419
420 /**
421 * bfq_update_active_node - recalculate min_start.
422 * @node: the node to update.
423 *
424 * @node may have changed position or one of its children may have moved,
425 * this function updates its min_start value. The left and right subtrees
426 * are assumed to hold a correct min_start value.
427 */
bfq_update_active_node(struct rb_node * node)428 static void bfq_update_active_node(struct rb_node *node)
429 {
430 struct bfq_entity *entity = rb_entry(node, struct bfq_entity, rb_node);
431
432 entity->min_start = entity->start;
433 bfq_update_min(entity, node->rb_right);
434 bfq_update_min(entity, node->rb_left);
435 }
436
437 /**
438 * bfq_update_active_tree - update min_start for the whole active tree.
439 * @node: the starting node.
440 *
441 * @node must be the deepest modified node after an update. This function
442 * updates its min_start using the values held by its children, assuming
443 * that they did not change, and then updates all the nodes that may have
444 * changed in the path to the root. The only nodes that may have changed
445 * are the ones in the path or their siblings.
446 */
bfq_update_active_tree(struct rb_node * node)447 static void bfq_update_active_tree(struct rb_node *node)
448 {
449 struct rb_node *parent;
450
451 up:
452 bfq_update_active_node(node);
453
454 parent = rb_parent(node);
455 if (!parent)
456 return;
457
458 if (node == parent->rb_left && parent->rb_right)
459 bfq_update_active_node(parent->rb_right);
460 else if (parent->rb_left)
461 bfq_update_active_node(parent->rb_left);
462
463 node = parent;
464 goto up;
465 }
466
467 /**
468 * bfq_active_insert - insert an entity in the active tree of its
469 * group/device.
470 * @st: the service tree of the entity.
471 * @entity: the entity being inserted.
472 *
473 * The active tree is ordered by finish time, but an extra key is kept
474 * per each node, containing the minimum value for the start times of
475 * its children (and the node itself), so it's possible to search for
476 * the eligible node with the lowest finish time in logarithmic time.
477 */
bfq_active_insert(struct bfq_service_tree * st,struct bfq_entity * entity)478 static void bfq_active_insert(struct bfq_service_tree *st,
479 struct bfq_entity *entity)
480 {
481 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
482 struct rb_node *node = &entity->rb_node;
483 #ifdef CONFIG_BFQ_GROUP_IOSCHED
484 struct bfq_sched_data *sd = NULL;
485 struct bfq_group *bfqg = NULL;
486 struct bfq_data *bfqd = NULL;
487 #endif
488
489 bfq_insert(&st->active, entity);
490
491 if (node->rb_left)
492 node = node->rb_left;
493 else if (node->rb_right)
494 node = node->rb_right;
495
496 bfq_update_active_tree(node);
497
498 #ifdef CONFIG_BFQ_GROUP_IOSCHED
499 sd = entity->sched_data;
500 bfqg = container_of(sd, struct bfq_group, sched_data);
501 bfqd = (struct bfq_data *)bfqg->bfqd;
502 #endif
503 if (bfqq)
504 list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list);
505 #ifdef CONFIG_BFQ_GROUP_IOSCHED
506 if (bfqg != bfqd->root_group)
507 bfqg->active_entities++;
508 #endif
509 }
510
511 /**
512 * bfq_ioprio_to_weight - calc a weight from an ioprio.
513 * @ioprio: the ioprio value to convert.
514 */
bfq_ioprio_to_weight(int ioprio)515 unsigned short bfq_ioprio_to_weight(int ioprio)
516 {
517 return (IOPRIO_BE_NR - ioprio) * BFQ_WEIGHT_CONVERSION_COEFF;
518 }
519
520 /**
521 * bfq_weight_to_ioprio - calc an ioprio from a weight.
522 * @weight: the weight value to convert.
523 *
524 * To preserve as much as possible the old only-ioprio user interface,
525 * 0 is used as an escape ioprio value for weights (numerically) equal or
526 * larger than IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF.
527 */
bfq_weight_to_ioprio(int weight)528 static unsigned short bfq_weight_to_ioprio(int weight)
529 {
530 return max_t(int, 0,
531 IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF - weight);
532 }
533
bfq_get_entity(struct bfq_entity * entity)534 static void bfq_get_entity(struct bfq_entity *entity)
535 {
536 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
537
538 if (bfqq) {
539 bfqq->ref++;
540 bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
541 bfqq, bfqq->ref);
542 }
543 }
544
545 /**
546 * bfq_find_deepest - find the deepest node that an extraction can modify.
547 * @node: the node being removed.
548 *
549 * Do the first step of an extraction in an rb tree, looking for the
550 * node that will replace @node, and returning the deepest node that
551 * the following modifications to the tree can touch. If @node is the
552 * last node in the tree return %NULL.
553 */
bfq_find_deepest(struct rb_node * node)554 static struct rb_node *bfq_find_deepest(struct rb_node *node)
555 {
556 struct rb_node *deepest;
557
558 if (!node->rb_right && !node->rb_left)
559 deepest = rb_parent(node);
560 else if (!node->rb_right)
561 deepest = node->rb_left;
562 else if (!node->rb_left)
563 deepest = node->rb_right;
564 else {
565 deepest = rb_next(node);
566 if (deepest->rb_right)
567 deepest = deepest->rb_right;
568 else if (rb_parent(deepest) != node)
569 deepest = rb_parent(deepest);
570 }
571
572 return deepest;
573 }
574
575 /**
576 * bfq_active_extract - remove an entity from the active tree.
577 * @st: the service_tree containing the tree.
578 * @entity: the entity being removed.
579 */
bfq_active_extract(struct bfq_service_tree * st,struct bfq_entity * entity)580 static void bfq_active_extract(struct bfq_service_tree *st,
581 struct bfq_entity *entity)
582 {
583 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
584 struct rb_node *node;
585 #ifdef CONFIG_BFQ_GROUP_IOSCHED
586 struct bfq_sched_data *sd = NULL;
587 struct bfq_group *bfqg = NULL;
588 struct bfq_data *bfqd = NULL;
589 #endif
590
591 node = bfq_find_deepest(&entity->rb_node);
592 bfq_extract(&st->active, entity);
593
594 if (node)
595 bfq_update_active_tree(node);
596
597 #ifdef CONFIG_BFQ_GROUP_IOSCHED
598 sd = entity->sched_data;
599 bfqg = container_of(sd, struct bfq_group, sched_data);
600 bfqd = (struct bfq_data *)bfqg->bfqd;
601 #endif
602 if (bfqq)
603 list_del(&bfqq->bfqq_list);
604 #ifdef CONFIG_BFQ_GROUP_IOSCHED
605 if (bfqg != bfqd->root_group)
606 bfqg->active_entities--;
607 #endif
608 }
609
610 /**
611 * bfq_idle_insert - insert an entity into the idle tree.
612 * @st: the service tree containing the tree.
613 * @entity: the entity to insert.
614 */
bfq_idle_insert(struct bfq_service_tree * st,struct bfq_entity * entity)615 static void bfq_idle_insert(struct bfq_service_tree *st,
616 struct bfq_entity *entity)
617 {
618 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
619 struct bfq_entity *first_idle = st->first_idle;
620 struct bfq_entity *last_idle = st->last_idle;
621
622 if (!first_idle || bfq_gt(first_idle->finish, entity->finish))
623 st->first_idle = entity;
624 if (!last_idle || bfq_gt(entity->finish, last_idle->finish))
625 st->last_idle = entity;
626
627 bfq_insert(&st->idle, entity);
628
629 if (bfqq)
630 list_add(&bfqq->bfqq_list, &bfqq->bfqd->idle_list);
631 }
632
633 /**
634 * bfq_forget_entity - do not consider entity any longer for scheduling
635 * @st: the service tree.
636 * @entity: the entity being removed.
637 * @is_in_service: true if entity is currently the in-service entity.
638 *
639 * Forget everything about @entity. In addition, if entity represents
640 * a queue, and the latter is not in service, then release the service
641 * reference to the queue (the one taken through bfq_get_entity). In
642 * fact, in this case, there is really no more service reference to
643 * the queue, as the latter is also outside any service tree. If,
644 * instead, the queue is in service, then __bfq_bfqd_reset_in_service
645 * will take care of putting the reference when the queue finally
646 * stops being served.
647 */
bfq_forget_entity(struct bfq_service_tree * st,struct bfq_entity * entity,bool is_in_service)648 static void bfq_forget_entity(struct bfq_service_tree *st,
649 struct bfq_entity *entity,
650 bool is_in_service)
651 {
652 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
653
654 entity->on_st = false;
655 st->wsum -= entity->weight;
656 if (bfqq && !is_in_service)
657 bfq_put_queue(bfqq);
658 }
659
660 /**
661 * bfq_put_idle_entity - release the idle tree ref of an entity.
662 * @st: service tree for the entity.
663 * @entity: the entity being released.
664 */
bfq_put_idle_entity(struct bfq_service_tree * st,struct bfq_entity * entity)665 void bfq_put_idle_entity(struct bfq_service_tree *st, struct bfq_entity *entity)
666 {
667 bfq_idle_extract(st, entity);
668 bfq_forget_entity(st, entity,
669 entity == entity->sched_data->in_service_entity);
670 }
671
672 /**
673 * bfq_forget_idle - update the idle tree if necessary.
674 * @st: the service tree to act upon.
675 *
676 * To preserve the global O(log N) complexity we only remove one entry here;
677 * as the idle tree will not grow indefinitely this can be done safely.
678 */
bfq_forget_idle(struct bfq_service_tree * st)679 static void bfq_forget_idle(struct bfq_service_tree *st)
680 {
681 struct bfq_entity *first_idle = st->first_idle;
682 struct bfq_entity *last_idle = st->last_idle;
683
684 if (RB_EMPTY_ROOT(&st->active) && last_idle &&
685 !bfq_gt(last_idle->finish, st->vtime)) {
686 /*
687 * Forget the whole idle tree, increasing the vtime past
688 * the last finish time of idle entities.
689 */
690 st->vtime = last_idle->finish;
691 }
692
693 if (first_idle && !bfq_gt(first_idle->finish, st->vtime))
694 bfq_put_idle_entity(st, first_idle);
695 }
696
bfq_entity_service_tree(struct bfq_entity * entity)697 struct bfq_service_tree *bfq_entity_service_tree(struct bfq_entity *entity)
698 {
699 struct bfq_sched_data *sched_data = entity->sched_data;
700 unsigned int idx = bfq_class_idx(entity);
701
702 return sched_data->service_tree + idx;
703 }
704
705 /*
706 * Update weight and priority of entity. If update_class_too is true,
707 * then update the ioprio_class of entity too.
708 *
709 * The reason why the update of ioprio_class is controlled through the
710 * last parameter is as follows. Changing the ioprio class of an
711 * entity implies changing the destination service trees for that
712 * entity. If such a change occurred when the entity is already on one
713 * of the service trees for its previous class, then the state of the
714 * entity would become more complex: none of the new possible service
715 * trees for the entity, according to bfq_entity_service_tree(), would
716 * match any of the possible service trees on which the entity
717 * is. Complex operations involving these trees, such as entity
718 * activations and deactivations, should take into account this
719 * additional complexity. To avoid this issue, this function is
720 * invoked with update_class_too unset in the points in the code where
721 * entity may happen to be on some tree.
722 */
723 struct bfq_service_tree *
__bfq_entity_update_weight_prio(struct bfq_service_tree * old_st,struct bfq_entity * entity,bool update_class_too)724 __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
725 struct bfq_entity *entity,
726 bool update_class_too)
727 {
728 struct bfq_service_tree *new_st = old_st;
729
730 if (entity->prio_changed) {
731 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
732 unsigned int prev_weight, new_weight;
733 struct bfq_data *bfqd = NULL;
734 struct rb_root *root;
735 #ifdef CONFIG_BFQ_GROUP_IOSCHED
736 struct bfq_sched_data *sd;
737 struct bfq_group *bfqg;
738 #endif
739
740 if (bfqq)
741 bfqd = bfqq->bfqd;
742 #ifdef CONFIG_BFQ_GROUP_IOSCHED
743 else {
744 sd = entity->my_sched_data;
745 bfqg = container_of(sd, struct bfq_group, sched_data);
746 bfqd = (struct bfq_data *)bfqg->bfqd;
747 }
748 #endif
749
750 old_st->wsum -= entity->weight;
751
752 if (entity->new_weight != entity->orig_weight) {
753 if (entity->new_weight < BFQ_MIN_WEIGHT ||
754 entity->new_weight > BFQ_MAX_WEIGHT) {
755 pr_crit("update_weight_prio: new_weight %d\n",
756 entity->new_weight);
757 if (entity->new_weight < BFQ_MIN_WEIGHT)
758 entity->new_weight = BFQ_MIN_WEIGHT;
759 else
760 entity->new_weight = BFQ_MAX_WEIGHT;
761 }
762 entity->orig_weight = entity->new_weight;
763 if (bfqq)
764 bfqq->ioprio =
765 bfq_weight_to_ioprio(entity->orig_weight);
766 }
767
768 if (bfqq && update_class_too)
769 bfqq->ioprio_class = bfqq->new_ioprio_class;
770
771 /*
772 * Reset prio_changed only if the ioprio_class change
773 * is not pending any longer.
774 */
775 if (!bfqq || bfqq->ioprio_class == bfqq->new_ioprio_class)
776 entity->prio_changed = 0;
777
778 /*
779 * NOTE: here we may be changing the weight too early,
780 * this will cause unfairness. The correct approach
781 * would have required additional complexity to defer
782 * weight changes to the proper time instants (i.e.,
783 * when entity->finish <= old_st->vtime).
784 */
785 new_st = bfq_entity_service_tree(entity);
786
787 prev_weight = entity->weight;
788 new_weight = entity->orig_weight *
789 (bfqq ? bfqq->wr_coeff : 1);
790 /*
791 * If the weight of the entity changes, and the entity is a
792 * queue, remove the entity from its old weight counter (if
793 * there is a counter associated with the entity).
794 */
795 if (prev_weight != new_weight && bfqq) {
796 root = &bfqd->queue_weights_tree;
797 __bfq_weights_tree_remove(bfqd, bfqq, root);
798 }
799 entity->weight = new_weight;
800 /*
801 * Add the entity, if it is not a weight-raised queue,
802 * to the counter associated with its new weight.
803 */
804 if (prev_weight != new_weight && bfqq && bfqq->wr_coeff == 1) {
805 /* If we get here, root has been initialized. */
806 bfq_weights_tree_add(bfqd, bfqq, root);
807 }
808
809 new_st->wsum += entity->weight;
810
811 if (new_st != old_st)
812 entity->start = new_st->vtime;
813 }
814
815 return new_st;
816 }
817
818 /**
819 * bfq_bfqq_served - update the scheduler status after selection for
820 * service.
821 * @bfqq: the queue being served.
822 * @served: bytes to transfer.
823 *
824 * NOTE: this can be optimized, as the timestamps of upper level entities
825 * are synchronized every time a new bfqq is selected for service. By now,
826 * we keep it to better check consistency.
827 */
bfq_bfqq_served(struct bfq_queue * bfqq,int served)828 void bfq_bfqq_served(struct bfq_queue *bfqq, int served)
829 {
830 struct bfq_entity *entity = &bfqq->entity;
831 struct bfq_service_tree *st;
832
833 if (!bfqq->service_from_backlogged)
834 bfqq->first_IO_time = jiffies;
835
836 if (bfqq->wr_coeff > 1)
837 bfqq->service_from_wr += served;
838
839 bfqq->service_from_backlogged += served;
840 for_each_entity(entity) {
841 st = bfq_entity_service_tree(entity);
842
843 entity->service += served;
844
845 st->vtime += bfq_delta(served, st->wsum);
846 bfq_forget_idle(st);
847 }
848 bfq_log_bfqq(bfqq->bfqd, bfqq, "bfqq_served %d secs", served);
849 }
850
851 /**
852 * bfq_bfqq_charge_time - charge an amount of service equivalent to the length
853 * of the time interval during which bfqq has been in
854 * service.
855 * @bfqd: the device
856 * @bfqq: the queue that needs a service update.
857 * @time_ms: the amount of time during which the queue has received service
858 *
859 * If a queue does not consume its budget fast enough, then providing
860 * the queue with service fairness may impair throughput, more or less
861 * severely. For this reason, queues that consume their budget slowly
862 * are provided with time fairness instead of service fairness. This
863 * goal is achieved through the BFQ scheduling engine, even if such an
864 * engine works in the service, and not in the time domain. The trick
865 * is charging these queues with an inflated amount of service, equal
866 * to the amount of service that they would have received during their
867 * service slot if they had been fast, i.e., if their requests had
868 * been dispatched at a rate equal to the estimated peak rate.
869 *
870 * It is worth noting that time fairness can cause important
871 * distortions in terms of bandwidth distribution, on devices with
872 * internal queueing. The reason is that I/O requests dispatched
873 * during the service slot of a queue may be served after that service
874 * slot is finished, and may have a total processing time loosely
875 * correlated with the duration of the service slot. This is
876 * especially true for short service slots.
877 */
bfq_bfqq_charge_time(struct bfq_data * bfqd,struct bfq_queue * bfqq,unsigned long time_ms)878 void bfq_bfqq_charge_time(struct bfq_data *bfqd, struct bfq_queue *bfqq,
879 unsigned long time_ms)
880 {
881 struct bfq_entity *entity = &bfqq->entity;
882 unsigned long timeout_ms = jiffies_to_msecs(bfq_timeout);
883 unsigned long bounded_time_ms = min(time_ms, timeout_ms);
884 int serv_to_charge_for_time =
885 (bfqd->bfq_max_budget * bounded_time_ms) / timeout_ms;
886 int tot_serv_to_charge = max(serv_to_charge_for_time, entity->service);
887
888 /* Increase budget to avoid inconsistencies */
889 if (tot_serv_to_charge > entity->budget)
890 entity->budget = tot_serv_to_charge;
891
892 bfq_bfqq_served(bfqq,
893 max_t(int, 0, tot_serv_to_charge - entity->service));
894 }
895
bfq_update_fin_time_enqueue(struct bfq_entity * entity,struct bfq_service_tree * st,bool backshifted)896 static void bfq_update_fin_time_enqueue(struct bfq_entity *entity,
897 struct bfq_service_tree *st,
898 bool backshifted)
899 {
900 struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
901
902 /*
903 * When this function is invoked, entity is not in any service
904 * tree, then it is safe to invoke next function with the last
905 * parameter set (see the comments on the function).
906 */
907 st = __bfq_entity_update_weight_prio(st, entity, true);
908 bfq_calc_finish(entity, entity->budget);
909
910 /*
911 * If some queues enjoy backshifting for a while, then their
912 * (virtual) finish timestamps may happen to become lower and
913 * lower than the system virtual time. In particular, if
914 * these queues often happen to be idle for short time
915 * periods, and during such time periods other queues with
916 * higher timestamps happen to be busy, then the backshifted
917 * timestamps of the former queues can become much lower than
918 * the system virtual time. In fact, to serve the queues with
919 * higher timestamps while the ones with lower timestamps are
920 * idle, the system virtual time may be pushed-up to much
921 * higher values than the finish timestamps of the idle
922 * queues. As a consequence, the finish timestamps of all new
923 * or newly activated queues may end up being much larger than
924 * those of lucky queues with backshifted timestamps. The
925 * latter queues may then monopolize the device for a lot of
926 * time. This would simply break service guarantees.
927 *
928 * To reduce this problem, push up a little bit the
929 * backshifted timestamps of the queue associated with this
930 * entity (only a queue can happen to have the backshifted
931 * flag set): just enough to let the finish timestamp of the
932 * queue be equal to the current value of the system virtual
933 * time. This may introduce a little unfairness among queues
934 * with backshifted timestamps, but it does not break
935 * worst-case fairness guarantees.
936 *
937 * As a special case, if bfqq is weight-raised, push up
938 * timestamps much less, to keep very low the probability that
939 * this push up causes the backshifted finish timestamps of
940 * weight-raised queues to become higher than the backshifted
941 * finish timestamps of non weight-raised queues.
942 */
943 if (backshifted && bfq_gt(st->vtime, entity->finish)) {
944 unsigned long delta = st->vtime - entity->finish;
945
946 if (bfqq)
947 delta /= bfqq->wr_coeff;
948
949 entity->start += delta;
950 entity->finish += delta;
951 }
952
953 bfq_active_insert(st, entity);
954 }
955
956 /**
957 * __bfq_activate_entity - handle activation of entity.
958 * @entity: the entity being activated.
959 * @non_blocking_wait_rq: true if entity was waiting for a request
960 *
961 * Called for a 'true' activation, i.e., if entity is not active and
962 * one of its children receives a new request.
963 *
964 * Basically, this function updates the timestamps of entity and
965 * inserts entity into its active tree, after possibly extracting it
966 * from its idle tree.
967 */
__bfq_activate_entity(struct bfq_entity * entity,bool non_blocking_wait_rq)968 static void __bfq_activate_entity(struct bfq_entity *entity,
969 bool non_blocking_wait_rq)
970 {
971 struct bfq_service_tree *st = bfq_entity_service_tree(entity);
972 bool backshifted = false;
973 unsigned long long min_vstart;
974
975 /* See comments on bfq_fqq_update_budg_for_activation */
976 if (non_blocking_wait_rq && bfq_gt(st->vtime, entity->finish)) {
977 backshifted = true;
978 min_vstart = entity->finish;
979 } else
980 min_vstart = st->vtime;
981
982 if (entity->tree == &st->idle) {
983 /*
984 * Must be on the idle tree, bfq_idle_extract() will
985 * check for that.
986 */
987 bfq_idle_extract(st, entity);
988 entity->start = bfq_gt(min_vstart, entity->finish) ?
989 min_vstart : entity->finish;
990 } else {
991 /*
992 * The finish time of the entity may be invalid, and
993 * it is in the past for sure, otherwise the queue
994 * would have been on the idle tree.
995 */
996 entity->start = min_vstart;
997 st->wsum += entity->weight;
998 /*
999 * entity is about to be inserted into a service tree,
1000 * and then set in service: get a reference to make
1001 * sure entity does not disappear until it is no
1002 * longer in service or scheduled for service.
1003 */
1004 bfq_get_entity(entity);
1005
1006 entity->on_st = true;
1007 }
1008
1009 #ifdef BFQ_GROUP_IOSCHED_ENABLED
1010 if (!bfq_entity_to_bfqq(entity)) { /* bfq_group */
1011 struct bfq_group *bfqg =
1012 container_of(entity, struct bfq_group, entity);
1013 struct bfq_data *bfqd = bfqg->bfqd;
1014
1015 if (!entity->in_groups_with_pending_reqs) {
1016 entity->in_groups_with_pending_reqs = true;
1017 bfqd->num_groups_with_pending_reqs++;
1018 }
1019 }
1020 #endif
1021
1022 bfq_update_fin_time_enqueue(entity, st, backshifted);
1023 }
1024
1025 /**
1026 * __bfq_requeue_entity - handle requeueing or repositioning of an entity.
1027 * @entity: the entity being requeued or repositioned.
1028 *
1029 * Requeueing is needed if this entity stops being served, which
1030 * happens if a leaf descendant entity has expired. On the other hand,
1031 * repositioning is needed if the next_inservice_entity for the child
1032 * entity has changed. See the comments inside the function for
1033 * details.
1034 *
1035 * Basically, this function: 1) removes entity from its active tree if
1036 * present there, 2) updates the timestamps of entity and 3) inserts
1037 * entity back into its active tree (in the new, right position for
1038 * the new values of the timestamps).
1039 */
__bfq_requeue_entity(struct bfq_entity * entity)1040 static void __bfq_requeue_entity(struct bfq_entity *entity)
1041 {
1042 struct bfq_sched_data *sd = entity->sched_data;
1043 struct bfq_service_tree *st = bfq_entity_service_tree(entity);
1044
1045 if (entity == sd->in_service_entity) {
1046 /*
1047 * We are requeueing the current in-service entity,
1048 * which may have to be done for one of the following
1049 * reasons:
1050 * - entity represents the in-service queue, and the
1051 * in-service queue is being requeued after an
1052 * expiration;
1053 * - entity represents a group, and its budget has
1054 * changed because one of its child entities has
1055 * just been either activated or requeued for some
1056 * reason; the timestamps of the entity need then to
1057 * be updated, and the entity needs to be enqueued
1058 * or repositioned accordingly.
1059 *
1060 * In particular, before requeueing, the start time of
1061 * the entity must be moved forward to account for the
1062 * service that the entity has received while in
1063 * service. This is done by the next instructions. The
1064 * finish time will then be updated according to this
1065 * new value of the start time, and to the budget of
1066 * the entity.
1067 */
1068 bfq_calc_finish(entity, entity->service);
1069 entity->start = entity->finish;
1070 /*
1071 * In addition, if the entity had more than one child
1072 * when set in service, then it was not extracted from
1073 * the active tree. This implies that the position of
1074 * the entity in the active tree may need to be
1075 * changed now, because we have just updated the start
1076 * time of the entity, and we will update its finish
1077 * time in a moment (the requeueing is then, more
1078 * precisely, a repositioning in this case). To
1079 * implement this repositioning, we: 1) dequeue the
1080 * entity here, 2) update the finish time and requeue
1081 * the entity according to the new timestamps below.
1082 */
1083 if (entity->tree)
1084 bfq_active_extract(st, entity);
1085 } else { /* The entity is already active, and not in service */
1086 /*
1087 * In this case, this function gets called only if the
1088 * next_in_service entity below this entity has
1089 * changed, and this change has caused the budget of
1090 * this entity to change, which, finally implies that
1091 * the finish time of this entity must be
1092 * updated. Such an update may cause the scheduling,
1093 * i.e., the position in the active tree, of this
1094 * entity to change. We handle this change by: 1)
1095 * dequeueing the entity here, 2) updating the finish
1096 * time and requeueing the entity according to the new
1097 * timestamps below. This is the same approach as the
1098 * non-extracted-entity sub-case above.
1099 */
1100 bfq_active_extract(st, entity);
1101 }
1102
1103 bfq_update_fin_time_enqueue(entity, st, false);
1104 }
1105
__bfq_activate_requeue_entity(struct bfq_entity * entity,struct bfq_sched_data * sd,bool non_blocking_wait_rq)1106 static void __bfq_activate_requeue_entity(struct bfq_entity *entity,
1107 struct bfq_sched_data *sd,
1108 bool non_blocking_wait_rq)
1109 {
1110 struct bfq_service_tree *st = bfq_entity_service_tree(entity);
1111
1112 if (sd->in_service_entity == entity || entity->tree == &st->active)
1113 /*
1114 * in service or already queued on the active tree,
1115 * requeue or reposition
1116 */
1117 __bfq_requeue_entity(entity);
1118 else
1119 /*
1120 * Not in service and not queued on its active tree:
1121 * the activity is idle and this is a true activation.
1122 */
1123 __bfq_activate_entity(entity, non_blocking_wait_rq);
1124 }
1125
1126
1127 /**
1128 * bfq_activate_requeue_entity - activate or requeue an entity representing a
1129 * bfq_queue, and activate, requeue or reposition
1130 * all ancestors for which such an update becomes
1131 * necessary.
1132 * @entity: the entity to activate.
1133 * @non_blocking_wait_rq: true if this entity was waiting for a request
1134 * @requeue: true if this is a requeue, which implies that bfqq is
1135 * being expired; thus ALL its ancestors stop being served and must
1136 * therefore be requeued
1137 * @expiration: true if this function is being invoked in the expiration path
1138 * of the in-service queue
1139 */
bfq_activate_requeue_entity(struct bfq_entity * entity,bool non_blocking_wait_rq,bool requeue,bool expiration)1140 static void bfq_activate_requeue_entity(struct bfq_entity *entity,
1141 bool non_blocking_wait_rq,
1142 bool requeue, bool expiration)
1143 {
1144 struct bfq_sched_data *sd;
1145
1146 for_each_entity(entity) {
1147 sd = entity->sched_data;
1148 __bfq_activate_requeue_entity(entity, sd, non_blocking_wait_rq);
1149
1150 if (!bfq_update_next_in_service(sd, entity, expiration) &&
1151 !requeue)
1152 break;
1153 }
1154 }
1155
1156 /**
1157 * __bfq_deactivate_entity - deactivate an entity from its service tree.
1158 * @entity: the entity to deactivate.
1159 * @ins_into_idle_tree: if false, the entity will not be put into the
1160 * idle tree.
1161 *
1162 * Deactivates an entity, independently of its previous state. Must
1163 * be invoked only if entity is on a service tree. Extracts the entity
1164 * from that tree, and if necessary and allowed, puts it into the idle
1165 * tree.
1166 */
__bfq_deactivate_entity(struct bfq_entity * entity,bool ins_into_idle_tree)1167 bool __bfq_deactivate_entity(struct bfq_entity *entity, bool ins_into_idle_tree)
1168 {
1169 struct bfq_sched_data *sd = entity->sched_data;
1170 struct bfq_service_tree *st;
1171 bool is_in_service;
1172
1173 if (!entity->on_st) /* entity never activated, or already inactive */
1174 return false;
1175
1176 /*
1177 * If we get here, then entity is active, which implies that
1178 * bfq_group_set_parent has already been invoked for the group
1179 * represented by entity. Therefore, the field
1180 * entity->sched_data has been set, and we can safely use it.
1181 */
1182 st = bfq_entity_service_tree(entity);
1183 is_in_service = entity == sd->in_service_entity;
1184
1185 bfq_calc_finish(entity, entity->service);
1186
1187 if (is_in_service)
1188 sd->in_service_entity = NULL;
1189 else
1190 /*
1191 * Non in-service entity: nobody will take care of
1192 * resetting its service counter on expiration. Do it
1193 * now.
1194 */
1195 entity->service = 0;
1196
1197 if (entity->tree == &st->active)
1198 bfq_active_extract(st, entity);
1199 else if (!is_in_service && entity->tree == &st->idle)
1200 bfq_idle_extract(st, entity);
1201
1202 if (!ins_into_idle_tree || !bfq_gt(entity->finish, st->vtime))
1203 bfq_forget_entity(st, entity, is_in_service);
1204 else
1205 bfq_idle_insert(st, entity);
1206
1207 return true;
1208 }
1209
1210 /**
1211 * bfq_deactivate_entity - deactivate an entity representing a bfq_queue.
1212 * @entity: the entity to deactivate.
1213 * @ins_into_idle_tree: true if the entity can be put into the idle tree
1214 * @expiration: true if this function is being invoked in the expiration path
1215 * of the in-service queue
1216 */
bfq_deactivate_entity(struct bfq_entity * entity,bool ins_into_idle_tree,bool expiration)1217 static void bfq_deactivate_entity(struct bfq_entity *entity,
1218 bool ins_into_idle_tree,
1219 bool expiration)
1220 {
1221 struct bfq_sched_data *sd;
1222 struct bfq_entity *parent = NULL;
1223
1224 for_each_entity_safe(entity, parent) {
1225 sd = entity->sched_data;
1226
1227 if (!__bfq_deactivate_entity(entity, ins_into_idle_tree)) {
1228 /*
1229 * entity is not in any tree any more, so
1230 * this deactivation is a no-op, and there is
1231 * nothing to change for upper-level entities
1232 * (in case of expiration, this can never
1233 * happen).
1234 */
1235 return;
1236 }
1237
1238 if (sd->next_in_service == entity)
1239 /*
1240 * entity was the next_in_service entity,
1241 * then, since entity has just been
1242 * deactivated, a new one must be found.
1243 */
1244 bfq_update_next_in_service(sd, NULL, expiration);
1245
1246 if (sd->next_in_service || sd->in_service_entity) {
1247 /*
1248 * The parent entity is still active, because
1249 * either next_in_service or in_service_entity
1250 * is not NULL. So, no further upwards
1251 * deactivation must be performed. Yet,
1252 * next_in_service has changed. Then the
1253 * schedule does need to be updated upwards.
1254 *
1255 * NOTE If in_service_entity is not NULL, then
1256 * next_in_service may happen to be NULL,
1257 * although the parent entity is evidently
1258 * active. This happens if 1) the entity
1259 * pointed by in_service_entity is the only
1260 * active entity in the parent entity, and 2)
1261 * according to the definition of
1262 * next_in_service, the in_service_entity
1263 * cannot be considered as
1264 * next_in_service. See the comments on the
1265 * definition of next_in_service for details.
1266 */
1267 break;
1268 }
1269
1270 /*
1271 * If we get here, then the parent is no more
1272 * backlogged and we need to propagate the
1273 * deactivation upwards. Thus let the loop go on.
1274 */
1275
1276 /*
1277 * Also let parent be queued into the idle tree on
1278 * deactivation, to preserve service guarantees, and
1279 * assuming that who invoked this function does not
1280 * need parent entities too to be removed completely.
1281 */
1282 ins_into_idle_tree = true;
1283 }
1284
1285 /*
1286 * If the deactivation loop is fully executed, then there are
1287 * no more entities to touch and next loop is not executed at
1288 * all. Otherwise, requeue remaining entities if they are
1289 * about to stop receiving service, or reposition them if this
1290 * is not the case.
1291 */
1292 entity = parent;
1293 for_each_entity(entity) {
1294 /*
1295 * Invoke __bfq_requeue_entity on entity, even if
1296 * already active, to requeue/reposition it in the
1297 * active tree (because sd->next_in_service has
1298 * changed)
1299 */
1300 __bfq_requeue_entity(entity);
1301
1302 sd = entity->sched_data;
1303 if (!bfq_update_next_in_service(sd, entity, expiration) &&
1304 !expiration)
1305 /*
1306 * next_in_service unchanged or not causing
1307 * any change in entity->parent->sd, and no
1308 * requeueing needed for expiration: stop
1309 * here.
1310 */
1311 break;
1312 }
1313 }
1314
1315 /**
1316 * bfq_calc_vtime_jump - compute the value to which the vtime should jump,
1317 * if needed, to have at least one entity eligible.
1318 * @st: the service tree to act upon.
1319 *
1320 * Assumes that st is not empty.
1321 */
bfq_calc_vtime_jump(struct bfq_service_tree * st)1322 static u64 bfq_calc_vtime_jump(struct bfq_service_tree *st)
1323 {
1324 struct bfq_entity *root_entity = bfq_root_active_entity(&st->active);
1325
1326 if (bfq_gt(root_entity->min_start, st->vtime))
1327 return root_entity->min_start;
1328
1329 return st->vtime;
1330 }
1331
bfq_update_vtime(struct bfq_service_tree * st,u64 new_value)1332 static void bfq_update_vtime(struct bfq_service_tree *st, u64 new_value)
1333 {
1334 if (new_value > st->vtime) {
1335 st->vtime = new_value;
1336 bfq_forget_idle(st);
1337 }
1338 }
1339
1340 /**
1341 * bfq_first_active_entity - find the eligible entity with
1342 * the smallest finish time
1343 * @st: the service tree to select from.
1344 * @vtime: the system virtual to use as a reference for eligibility
1345 *
1346 * This function searches the first schedulable entity, starting from the
1347 * root of the tree and going on the left every time on this side there is
1348 * a subtree with at least one eligible (start <= vtime) entity. The path on
1349 * the right is followed only if a) the left subtree contains no eligible
1350 * entities and b) no eligible entity has been found yet.
1351 */
bfq_first_active_entity(struct bfq_service_tree * st,u64 vtime)1352 static struct bfq_entity *bfq_first_active_entity(struct bfq_service_tree *st,
1353 u64 vtime)
1354 {
1355 struct bfq_entity *entry, *first = NULL;
1356 struct rb_node *node = st->active.rb_node;
1357
1358 while (node) {
1359 entry = rb_entry(node, struct bfq_entity, rb_node);
1360 left:
1361 if (!bfq_gt(entry->start, vtime))
1362 first = entry;
1363
1364 if (node->rb_left) {
1365 entry = rb_entry(node->rb_left,
1366 struct bfq_entity, rb_node);
1367 if (!bfq_gt(entry->min_start, vtime)) {
1368 node = node->rb_left;
1369 goto left;
1370 }
1371 }
1372 if (first)
1373 break;
1374 node = node->rb_right;
1375 }
1376
1377 return first;
1378 }
1379
1380 /**
1381 * __bfq_lookup_next_entity - return the first eligible entity in @st.
1382 * @st: the service tree.
1383 *
1384 * If there is no in-service entity for the sched_data st belongs to,
1385 * then return the entity that will be set in service if:
1386 * 1) the parent entity this st belongs to is set in service;
1387 * 2) no entity belonging to such parent entity undergoes a state change
1388 * that would influence the timestamps of the entity (e.g., becomes idle,
1389 * becomes backlogged, changes its budget, ...).
1390 *
1391 * In this first case, update the virtual time in @st too (see the
1392 * comments on this update inside the function).
1393 *
1394 * In constrast, if there is an in-service entity, then return the
1395 * entity that would be set in service if not only the above
1396 * conditions, but also the next one held true: the currently
1397 * in-service entity, on expiration,
1398 * 1) gets a finish time equal to the current one, or
1399 * 2) is not eligible any more, or
1400 * 3) is idle.
1401 */
1402 static struct bfq_entity *
__bfq_lookup_next_entity(struct bfq_service_tree * st,bool in_service)1403 __bfq_lookup_next_entity(struct bfq_service_tree *st, bool in_service)
1404 {
1405 struct bfq_entity *entity;
1406 u64 new_vtime;
1407
1408 if (RB_EMPTY_ROOT(&st->active))
1409 return NULL;
1410
1411 /*
1412 * Get the value of the system virtual time for which at
1413 * least one entity is eligible.
1414 */
1415 new_vtime = bfq_calc_vtime_jump(st);
1416
1417 /*
1418 * If there is no in-service entity for the sched_data this
1419 * active tree belongs to, then push the system virtual time
1420 * up to the value that guarantees that at least one entity is
1421 * eligible. If, instead, there is an in-service entity, then
1422 * do not make any such update, because there is already an
1423 * eligible entity, namely the in-service one (even if the
1424 * entity is not on st, because it was extracted when set in
1425 * service).
1426 */
1427 if (!in_service)
1428 bfq_update_vtime(st, new_vtime);
1429
1430 entity = bfq_first_active_entity(st, new_vtime);
1431
1432 return entity;
1433 }
1434
1435 /**
1436 * bfq_lookup_next_entity - return the first eligible entity in @sd.
1437 * @sd: the sched_data.
1438 * @expiration: true if we are on the expiration path of the in-service queue
1439 *
1440 * This function is invoked when there has been a change in the trees
1441 * for sd, and we need to know what is the new next entity to serve
1442 * after this change.
1443 */
bfq_lookup_next_entity(struct bfq_sched_data * sd,bool expiration)1444 static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
1445 bool expiration)
1446 {
1447 struct bfq_service_tree *st = sd->service_tree;
1448 struct bfq_service_tree *idle_class_st = st + (BFQ_IOPRIO_CLASSES - 1);
1449 struct bfq_entity *entity = NULL;
1450 int class_idx = 0;
1451
1452 /*
1453 * Choose from idle class, if needed to guarantee a minimum
1454 * bandwidth to this class (and if there is some active entity
1455 * in idle class). This should also mitigate
1456 * priority-inversion problems in case a low priority task is
1457 * holding file system resources.
1458 */
1459 if (time_is_before_jiffies(sd->bfq_class_idle_last_service +
1460 BFQ_CL_IDLE_TIMEOUT)) {
1461 if (!RB_EMPTY_ROOT(&idle_class_st->active))
1462 class_idx = BFQ_IOPRIO_CLASSES - 1;
1463 /* About to be served if backlogged, or not yet backlogged */
1464 sd->bfq_class_idle_last_service = jiffies;
1465 }
1466
1467 /*
1468 * Find the next entity to serve for the highest-priority
1469 * class, unless the idle class needs to be served.
1470 */
1471 for (; class_idx < BFQ_IOPRIO_CLASSES; class_idx++) {
1472 /*
1473 * If expiration is true, then bfq_lookup_next_entity
1474 * is being invoked as a part of the expiration path
1475 * of the in-service queue. In this case, even if
1476 * sd->in_service_entity is not NULL,
1477 * sd->in_service_entiy at this point is actually not
1478 * in service any more, and, if needed, has already
1479 * been properly queued or requeued into the right
1480 * tree. The reason why sd->in_service_entity is still
1481 * not NULL here, even if expiration is true, is that
1482 * sd->in_service_entiy is reset as a last step in the
1483 * expiration path. So, if expiration is true, tell
1484 * __bfq_lookup_next_entity that there is no
1485 * sd->in_service_entity.
1486 */
1487 entity = __bfq_lookup_next_entity(st + class_idx,
1488 sd->in_service_entity &&
1489 !expiration);
1490
1491 if (entity)
1492 break;
1493 }
1494
1495 if (!entity)
1496 return NULL;
1497
1498 return entity;
1499 }
1500
next_queue_may_preempt(struct bfq_data * bfqd)1501 bool next_queue_may_preempt(struct bfq_data *bfqd)
1502 {
1503 struct bfq_sched_data *sd = &bfqd->root_group->sched_data;
1504
1505 return sd->next_in_service != sd->in_service_entity;
1506 }
1507
1508 /*
1509 * Get next queue for service.
1510 */
bfq_get_next_queue(struct bfq_data * bfqd)1511 struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd)
1512 {
1513 struct bfq_entity *entity = NULL;
1514 struct bfq_sched_data *sd;
1515 struct bfq_queue *bfqq;
1516
1517 if (bfqd->busy_queues == 0)
1518 return NULL;
1519
1520 /*
1521 * Traverse the path from the root to the leaf entity to
1522 * serve. Set in service all the entities visited along the
1523 * way.
1524 */
1525 sd = &bfqd->root_group->sched_data;
1526 for (; sd ; sd = entity->my_sched_data) {
1527 /*
1528 * WARNING. We are about to set the in-service entity
1529 * to sd->next_in_service, i.e., to the (cached) value
1530 * returned by bfq_lookup_next_entity(sd) the last
1531 * time it was invoked, i.e., the last time when the
1532 * service order in sd changed as a consequence of the
1533 * activation or deactivation of an entity. In this
1534 * respect, if we execute bfq_lookup_next_entity(sd)
1535 * in this very moment, it may, although with low
1536 * probability, yield a different entity than that
1537 * pointed to by sd->next_in_service. This rare event
1538 * happens in case there was no CLASS_IDLE entity to
1539 * serve for sd when bfq_lookup_next_entity(sd) was
1540 * invoked for the last time, while there is now one
1541 * such entity.
1542 *
1543 * If the above event happens, then the scheduling of
1544 * such entity in CLASS_IDLE is postponed until the
1545 * service of the sd->next_in_service entity
1546 * finishes. In fact, when the latter is expired,
1547 * bfq_lookup_next_entity(sd) gets called again,
1548 * exactly to update sd->next_in_service.
1549 */
1550
1551 /* Make next_in_service entity become in_service_entity */
1552 entity = sd->next_in_service;
1553 sd->in_service_entity = entity;
1554
1555 /*
1556 * If entity is no longer a candidate for next
1557 * service, then it must be extracted from its active
1558 * tree, so as to make sure that it won't be
1559 * considered when computing next_in_service. See the
1560 * comments on the function
1561 * bfq_no_longer_next_in_service() for details.
1562 */
1563 if (bfq_no_longer_next_in_service(entity))
1564 bfq_active_extract(bfq_entity_service_tree(entity),
1565 entity);
1566
1567 /*
1568 * Even if entity is not to be extracted according to
1569 * the above check, a descendant entity may get
1570 * extracted in one of the next iterations of this
1571 * loop. Such an event could cause a change in
1572 * next_in_service for the level of the descendant
1573 * entity, and thus possibly back to this level.
1574 *
1575 * However, we cannot perform the resulting needed
1576 * update of next_in_service for this level before the
1577 * end of the whole loop, because, to know which is
1578 * the correct next-to-serve candidate entity for each
1579 * level, we need first to find the leaf entity to set
1580 * in service. In fact, only after we know which is
1581 * the next-to-serve leaf entity, we can discover
1582 * whether the parent entity of the leaf entity
1583 * becomes the next-to-serve, and so on.
1584 */
1585 }
1586
1587 bfqq = bfq_entity_to_bfqq(entity);
1588
1589 /*
1590 * We can finally update all next-to-serve entities along the
1591 * path from the leaf entity just set in service to the root.
1592 */
1593 for_each_entity(entity) {
1594 struct bfq_sched_data *sd = entity->sched_data;
1595
1596 if (!bfq_update_next_in_service(sd, NULL, false))
1597 break;
1598 }
1599
1600 return bfqq;
1601 }
1602
1603 /* returns true if the in-service queue gets freed */
__bfq_bfqd_reset_in_service(struct bfq_data * bfqd)1604 bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
1605 {
1606 struct bfq_queue *in_serv_bfqq = bfqd->in_service_queue;
1607 struct bfq_entity *in_serv_entity = &in_serv_bfqq->entity;
1608 struct bfq_entity *entity = in_serv_entity;
1609
1610 bfq_clear_bfqq_wait_request(in_serv_bfqq);
1611 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
1612 bfqd->in_service_queue = NULL;
1613
1614 /*
1615 * When this function is called, all in-service entities have
1616 * been properly deactivated or requeued, so we can safely
1617 * execute the final step: reset in_service_entity along the
1618 * path from entity to the root.
1619 */
1620 for_each_entity(entity)
1621 entity->sched_data->in_service_entity = NULL;
1622
1623 /*
1624 * in_serv_entity is no longer in service, so, if it is in no
1625 * service tree either, then release the service reference to
1626 * the queue it represents (taken with bfq_get_entity).
1627 */
1628 if (!in_serv_entity->on_st) {
1629 /*
1630 * If no process is referencing in_serv_bfqq any
1631 * longer, then the service reference may be the only
1632 * reference to the queue. If this is the case, then
1633 * bfqq gets freed here.
1634 */
1635 int ref = in_serv_bfqq->ref;
1636 bfq_put_queue(in_serv_bfqq);
1637 if (ref == 1)
1638 return true;
1639 }
1640
1641 return false;
1642 }
1643
bfq_deactivate_bfqq(struct bfq_data * bfqd,struct bfq_queue * bfqq,bool ins_into_idle_tree,bool expiration)1644 void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
1645 bool ins_into_idle_tree, bool expiration)
1646 {
1647 struct bfq_entity *entity = &bfqq->entity;
1648
1649 bfq_deactivate_entity(entity, ins_into_idle_tree, expiration);
1650 }
1651
bfq_activate_bfqq(struct bfq_data * bfqd,struct bfq_queue * bfqq)1652 void bfq_activate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1653 {
1654 struct bfq_entity *entity = &bfqq->entity;
1655
1656 bfq_activate_requeue_entity(entity, bfq_bfqq_non_blocking_wait_rq(bfqq),
1657 false, false);
1658 bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1659 }
1660
bfq_requeue_bfqq(struct bfq_data * bfqd,struct bfq_queue * bfqq,bool expiration)1661 void bfq_requeue_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
1662 bool expiration)
1663 {
1664 struct bfq_entity *entity = &bfqq->entity;
1665
1666 bfq_activate_requeue_entity(entity, false,
1667 bfqq == bfqd->in_service_queue, expiration);
1668 }
1669
1670 /*
1671 * Called when the bfqq no longer has requests pending, remove it from
1672 * the service tree. As a special case, it can be invoked during an
1673 * expiration.
1674 */
bfq_del_bfqq_busy(struct bfq_data * bfqd,struct bfq_queue * bfqq,bool expiration)1675 void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
1676 bool expiration)
1677 {
1678 bfq_log_bfqq(bfqd, bfqq, "del from busy");
1679
1680 bfq_clear_bfqq_busy(bfqq);
1681
1682 bfqd->busy_queues--;
1683
1684 if (bfqq->wr_coeff > 1)
1685 bfqd->wr_busy_queues--;
1686
1687 bfqg_stats_update_dequeue(bfqq_group(bfqq));
1688
1689 bfq_deactivate_bfqq(bfqd, bfqq, true, expiration);
1690
1691 if (!bfqq->dispatched)
1692 bfq_weights_tree_remove(bfqd, bfqq);
1693 }
1694
1695 /*
1696 * Called when an inactive queue receives a new request.
1697 */
bfq_add_bfqq_busy(struct bfq_data * bfqd,struct bfq_queue * bfqq)1698 void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1699 {
1700 bfq_log_bfqq(bfqd, bfqq, "add to busy");
1701
1702 bfq_activate_bfqq(bfqd, bfqq);
1703
1704 bfq_mark_bfqq_busy(bfqq);
1705 bfqd->busy_queues++;
1706
1707 if (!bfqq->dispatched)
1708 if (bfqq->wr_coeff == 1)
1709 bfq_weights_tree_add(bfqd, bfqq,
1710 &bfqd->queue_weights_tree);
1711
1712 if (bfqq->wr_coeff > 1)
1713 bfqd->wr_busy_queues++;
1714 }
1715