Root/block/blk-throttle.c

1/*
2 * Interface for controlling IO bandwidth on a request queue
3 *
4 * Copyright (C) 2010 Vivek Goyal <vgoyal@redhat.com>
5 */
6
7#include <linux/module.h>
8#include <linux/slab.h>
9#include <linux/blkdev.h>
10#include <linux/bio.h>
11#include <linux/blktrace_api.h>
12#include "blk-cgroup.h"
13#include "blk.h"
14
15/* Max dispatch from a group in 1 round */
16static int throtl_grp_quantum = 8;
17
18/* Total max dispatch from all groups in one round */
19static int throtl_quantum = 32;
20
21/* Throttling is performed over 100ms slice and after that slice is renewed */
22static unsigned long throtl_slice = HZ/10; /* 100 ms */
23
24static struct blkcg_policy blkcg_policy_throtl;
25
26/* A workqueue to queue throttle related work */
27static struct workqueue_struct *kthrotld_workqueue;
28
29/*
30 * To implement hierarchical throttling, throtl_grps form a tree and bios
31 * are dispatched upwards level by level until they reach the top and get
32 * issued. When dispatching bios from the children and local group at each
33 * level, if the bios are dispatched into a single bio_list, there's a risk
34 * of a local or child group which can queue many bios at once filling up
35 * the list starving others.
36 *
37 * To avoid such starvation, dispatched bios are queued separately
38 * according to where they came from. When they are again dispatched to
39 * the parent, they're popped in round-robin order so that no single source
40 * hogs the dispatch window.
41 *
42 * throtl_qnode is used to keep the queued bios separated by their sources.
43 * Bios are queued to throtl_qnode which in turn is queued to
44 * throtl_service_queue and then dispatched in round-robin order.
45 *
46 * It's also used to track the reference counts on blkg's. A qnode always
47 * belongs to a throtl_grp and gets queued on itself or the parent, so
48 * incrementing the reference of the associated throtl_grp when a qnode is
49 * queued and decrementing when dequeued is enough to keep the whole blkg
50 * tree pinned while bios are in flight.
51 */
52struct throtl_qnode {
53    struct list_head node; /* service_queue->queued[] */
54    struct bio_list bios; /* queued bios */
55    struct throtl_grp *tg; /* tg this qnode belongs to */
56};
57
58struct throtl_service_queue {
59    struct throtl_service_queue *parent_sq; /* the parent service_queue */
60
61    /*
62     * Bios queued directly to this service_queue or dispatched from
63     * children throtl_grp's.
64     */
65    struct list_head queued[2]; /* throtl_qnode [READ/WRITE] */
66    unsigned int nr_queued[2]; /* number of queued bios */
67
68    /*
69     * RB tree of active children throtl_grp's, which are sorted by
70     * their ->disptime.
71     */
72    struct rb_root pending_tree; /* RB tree of active tgs */
73    struct rb_node *first_pending; /* first node in the tree */
74    unsigned int nr_pending; /* # queued in the tree */
75    unsigned long first_pending_disptime; /* disptime of the first tg */
76    struct timer_list pending_timer; /* fires on first_pending_disptime */
77};
78
79enum tg_state_flags {
80    THROTL_TG_PENDING = 1 << 0, /* on parent's pending tree */
81    THROTL_TG_WAS_EMPTY = 1 << 1, /* bio_lists[] became non-empty */
82};
83
84#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)
85
86/* Per-cpu group stats */
87struct tg_stats_cpu {
88    /* total bytes transferred */
89    struct blkg_rwstat service_bytes;
90    /* total IOs serviced, post merge */
91    struct blkg_rwstat serviced;
92};
93
94struct throtl_grp {
95    /* must be the first member */
96    struct blkg_policy_data pd;
97
98    /* active throtl group service_queue member */
99    struct rb_node rb_node;
100
101    /* throtl_data this group belongs to */
102    struct throtl_data *td;
103
104    /* this group's service queue */
105    struct throtl_service_queue service_queue;
106
107    /*
108     * qnode_on_self is used when bios are directly queued to this
109     * throtl_grp so that local bios compete fairly with bios
110     * dispatched from children. qnode_on_parent is used when bios are
111     * dispatched from this throtl_grp into its parent and will compete
112     * with the sibling qnode_on_parents and the parent's
113     * qnode_on_self.
114     */
115    struct throtl_qnode qnode_on_self[2];
116    struct throtl_qnode qnode_on_parent[2];
117
118    /*
119     * Dispatch time in jiffies. This is the estimated time when group
120     * will unthrottle and is ready to dispatch more bio. It is used as
121     * key to sort active groups in service tree.
122     */
123    unsigned long disptime;
124
125    unsigned int flags;
126
127    /* are there any throtl rules between this group and td? */
128    bool has_rules[2];
129
130    /* bytes per second rate limits */
131    uint64_t bps[2];
132
133    /* IOPS limits */
134    unsigned int iops[2];
135
136    /* Number of bytes disptached in current slice */
137    uint64_t bytes_disp[2];
138    /* Number of bio's dispatched in current slice */
139    unsigned int io_disp[2];
140
141    /* When did we start a new slice */
142    unsigned long slice_start[2];
143    unsigned long slice_end[2];
144
145    /* Per cpu stats pointer */
146    struct tg_stats_cpu __percpu *stats_cpu;
147
148    /* List of tgs waiting for per cpu stats memory to be allocated */
149    struct list_head stats_alloc_node;
150};
151
152struct throtl_data
153{
154    /* service tree for active throtl groups */
155    struct throtl_service_queue service_queue;
156
157    struct request_queue *queue;
158
159    /* Total Number of queued bios on READ and WRITE lists */
160    unsigned int nr_queued[2];
161
162    /*
163     * number of total undestroyed groups
164     */
165    unsigned int nr_undestroyed_grps;
166
167    /* Work for dispatching throttled bios */
168    struct work_struct dispatch_work;
169};
170
171/* list and work item to allocate percpu group stats */
172static DEFINE_SPINLOCK(tg_stats_alloc_lock);
173static LIST_HEAD(tg_stats_alloc_list);
174
175static void tg_stats_alloc_fn(struct work_struct *);
176static DECLARE_DELAYED_WORK(tg_stats_alloc_work, tg_stats_alloc_fn);
177
178static void throtl_pending_timer_fn(unsigned long arg);
179
180static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
181{
182    return pd ? container_of(pd, struct throtl_grp, pd) : NULL;
183}
184
185static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg)
186{
187    return pd_to_tg(blkg_to_pd(blkg, &blkcg_policy_throtl));
188}
189
190static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
191{
192    return pd_to_blkg(&tg->pd);
193}
194
195static inline struct throtl_grp *td_root_tg(struct throtl_data *td)
196{
197    return blkg_to_tg(td->queue->root_blkg);
198}
199
200/**
201 * sq_to_tg - return the throl_grp the specified service queue belongs to
202 * @sq: the throtl_service_queue of interest
203 *
204 * Return the throtl_grp @sq belongs to. If @sq is the top-level one
205 * embedded in throtl_data, %NULL is returned.
206 */
207static struct throtl_grp *sq_to_tg(struct throtl_service_queue *sq)
208{
209    if (sq && sq->parent_sq)
210        return container_of(sq, struct throtl_grp, service_queue);
211    else
212        return NULL;
213}
214
215/**
216 * sq_to_td - return throtl_data the specified service queue belongs to
217 * @sq: the throtl_service_queue of interest
218 *
219 * A service_queue can be embeded in either a throtl_grp or throtl_data.
220 * Determine the associated throtl_data accordingly and return it.
221 */
222static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
223{
224    struct throtl_grp *tg = sq_to_tg(sq);
225
226    if (tg)
227        return tg->td;
228    else
229        return container_of(sq, struct throtl_data, service_queue);
230}
231
232/**
233 * throtl_log - log debug message via blktrace
234 * @sq: the service_queue being reported
235 * @fmt: printf format string
236 * @args: printf args
237 *
238 * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
239 * throtl_grp; otherwise, just "throtl".
240 *
241 * TODO: this should be made a function and name formatting should happen
242 * after testing whether blktrace is enabled.
243 */
244#define throtl_log(sq, fmt, args...) do { \
245    struct throtl_grp *__tg = sq_to_tg((sq)); \
246    struct throtl_data *__td = sq_to_td((sq)); \
247                                    \
248    (void)__td; \
249    if ((__tg)) { \
250        char __pbuf[128]; \
251                                    \
252        blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf)); \
253        blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \
254    } else { \
255        blk_add_trace_msg(__td->queue, "throtl " fmt, ##args); \
256    } \
257} while (0)
258
259static void tg_stats_init(struct tg_stats_cpu *tg_stats)
260{
261    blkg_rwstat_init(&tg_stats->service_bytes);
262    blkg_rwstat_init(&tg_stats->serviced);
263}
264
265/*
266 * Worker for allocating per cpu stat for tgs. This is scheduled on the
267 * system_wq once there are some groups on the alloc_list waiting for
268 * allocation.
269 */
270static void tg_stats_alloc_fn(struct work_struct *work)
271{
272    static struct tg_stats_cpu *stats_cpu; /* this fn is non-reentrant */
273    struct delayed_work *dwork = to_delayed_work(work);
274    bool empty = false;
275
276alloc_stats:
277    if (!stats_cpu) {
278        int cpu;
279
280        stats_cpu = alloc_percpu(struct tg_stats_cpu);
281        if (!stats_cpu) {
282            /* allocation failed, try again after some time */
283            schedule_delayed_work(dwork, msecs_to_jiffies(10));
284            return;
285        }
286        for_each_possible_cpu(cpu)
287            tg_stats_init(per_cpu_ptr(stats_cpu, cpu));
288    }
289
290    spin_lock_irq(&tg_stats_alloc_lock);
291
292    if (!list_empty(&tg_stats_alloc_list)) {
293        struct throtl_grp *tg = list_first_entry(&tg_stats_alloc_list,
294                             struct throtl_grp,
295                             stats_alloc_node);
296        swap(tg->stats_cpu, stats_cpu);
297        list_del_init(&tg->stats_alloc_node);
298    }
299
300    empty = list_empty(&tg_stats_alloc_list);
301    spin_unlock_irq(&tg_stats_alloc_lock);
302    if (!empty)
303        goto alloc_stats;
304}
305
306static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
307{
308    INIT_LIST_HEAD(&qn->node);
309    bio_list_init(&qn->bios);
310    qn->tg = tg;
311}
312
313/**
314 * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it
315 * @bio: bio being added
316 * @qn: qnode to add bio to
317 * @queued: the service_queue->queued[] list @qn belongs to
318 *
319 * Add @bio to @qn and put @qn on @queued if it's not already on.
320 * @qn->tg's reference count is bumped when @qn is activated. See the
321 * comment on top of throtl_qnode definition for details.
322 */
323static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn,
324                 struct list_head *queued)
325{
326    bio_list_add(&qn->bios, bio);
327    if (list_empty(&qn->node)) {
328        list_add_tail(&qn->node, queued);
329        blkg_get(tg_to_blkg(qn->tg));
330    }
331}
332
333/**
334 * throtl_peek_queued - peek the first bio on a qnode list
335 * @queued: the qnode list to peek
336 */
337static struct bio *throtl_peek_queued(struct list_head *queued)
338{
339    struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
340    struct bio *bio;
341
342    if (list_empty(queued))
343        return NULL;
344
345    bio = bio_list_peek(&qn->bios);
346    WARN_ON_ONCE(!bio);
347    return bio;
348}
349
350/**
351 * throtl_pop_queued - pop the first bio form a qnode list
352 * @queued: the qnode list to pop a bio from
353 * @tg_to_put: optional out argument for throtl_grp to put
354 *
355 * Pop the first bio from the qnode list @queued. After popping, the first
356 * qnode is removed from @queued if empty or moved to the end of @queued so
357 * that the popping order is round-robin.
358 *
359 * When the first qnode is removed, its associated throtl_grp should be put
360 * too. If @tg_to_put is NULL, this function automatically puts it;
361 * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is
362 * responsible for putting it.
363 */
364static struct bio *throtl_pop_queued(struct list_head *queued,
365                     struct throtl_grp **tg_to_put)
366{
367    struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
368    struct bio *bio;
369
370    if (list_empty(queued))
371        return NULL;
372
373    bio = bio_list_pop(&qn->bios);
374    WARN_ON_ONCE(!bio);
375
376    if (bio_list_empty(&qn->bios)) {
377        list_del_init(&qn->node);
378        if (tg_to_put)
379            *tg_to_put = qn->tg;
380        else
381            blkg_put(tg_to_blkg(qn->tg));
382    } else {
383        list_move_tail(&qn->node, queued);
384    }
385
386    return bio;
387}
388
389/* init a service_queue, assumes the caller zeroed it */
390static void throtl_service_queue_init(struct throtl_service_queue *sq,
391                      struct throtl_service_queue *parent_sq)
392{
393    INIT_LIST_HEAD(&sq->queued[0]);
394    INIT_LIST_HEAD(&sq->queued[1]);
395    sq->pending_tree = RB_ROOT;
396    sq->parent_sq = parent_sq;
397    setup_timer(&sq->pending_timer, throtl_pending_timer_fn,
398            (unsigned long)sq);
399}
400
401static void throtl_service_queue_exit(struct throtl_service_queue *sq)
402{
403    del_timer_sync(&sq->pending_timer);
404}
405
406static void throtl_pd_init(struct blkcg_gq *blkg)
407{
408    struct throtl_grp *tg = blkg_to_tg(blkg);
409    struct throtl_data *td = blkg->q->td;
410    struct throtl_service_queue *parent_sq;
411    unsigned long flags;
412    int rw;
413
414    /*
415     * If sane_hierarchy is enabled, we switch to properly hierarchical
416     * behavior where limits on a given throtl_grp are applied to the
417     * whole subtree rather than just the group itself. e.g. If 16M
418     * read_bps limit is set on the root group, the whole system can't
419     * exceed 16M for the device.
420     *
421     * If sane_hierarchy is not enabled, the broken flat hierarchy
422     * behavior is retained where all throtl_grps are treated as if
423     * they're all separate root groups right below throtl_data.
424     * Limits of a group don't interact with limits of other groups
425     * regardless of the position of the group in the hierarchy.
426     */
427    parent_sq = &td->service_queue;
428
429    if (cgroup_sane_behavior(blkg->blkcg->css.cgroup) && blkg->parent)
430        parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
431
432    throtl_service_queue_init(&tg->service_queue, parent_sq);
433
434    for (rw = READ; rw <= WRITE; rw++) {
435        throtl_qnode_init(&tg->qnode_on_self[rw], tg);
436        throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
437    }
438
439    RB_CLEAR_NODE(&tg->rb_node);
440    tg->td = td;
441
442    tg->bps[READ] = -1;
443    tg->bps[WRITE] = -1;
444    tg->iops[READ] = -1;
445    tg->iops[WRITE] = -1;
446
447    /*
448     * Ugh... We need to perform per-cpu allocation for tg->stats_cpu
449     * but percpu allocator can't be called from IO path. Queue tg on
450     * tg_stats_alloc_list and allocate from work item.
451     */
452    spin_lock_irqsave(&tg_stats_alloc_lock, flags);
453    list_add(&tg->stats_alloc_node, &tg_stats_alloc_list);
454    schedule_delayed_work(&tg_stats_alloc_work, 0);
455    spin_unlock_irqrestore(&tg_stats_alloc_lock, flags);
456}
457
458/*
459 * Set has_rules[] if @tg or any of its parents have limits configured.
460 * This doesn't require walking up to the top of the hierarchy as the
461 * parent's has_rules[] is guaranteed to be correct.
462 */
463static void tg_update_has_rules(struct throtl_grp *tg)
464{
465    struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
466    int rw;
467
468    for (rw = READ; rw <= WRITE; rw++)
469        tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
470                    (tg->bps[rw] != -1 || tg->iops[rw] != -1);
471}
472
473static void throtl_pd_online(struct blkcg_gq *blkg)
474{
475    /*
476     * We don't want new groups to escape the limits of its ancestors.
477     * Update has_rules[] after a new group is brought online.
478     */
479    tg_update_has_rules(blkg_to_tg(blkg));
480}
481
482static void throtl_pd_exit(struct blkcg_gq *blkg)
483{
484    struct throtl_grp *tg = blkg_to_tg(blkg);
485    unsigned long flags;
486
487    spin_lock_irqsave(&tg_stats_alloc_lock, flags);
488    list_del_init(&tg->stats_alloc_node);
489    spin_unlock_irqrestore(&tg_stats_alloc_lock, flags);
490
491    free_percpu(tg->stats_cpu);
492
493    throtl_service_queue_exit(&tg->service_queue);
494}
495
496static void throtl_pd_reset_stats(struct blkcg_gq *blkg)
497{
498    struct throtl_grp *tg = blkg_to_tg(blkg);
499    int cpu;
500
501    if (tg->stats_cpu == NULL)
502        return;
503
504    for_each_possible_cpu(cpu) {
505        struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);
506
507        blkg_rwstat_reset(&sc->service_bytes);
508        blkg_rwstat_reset(&sc->serviced);
509    }
510}
511
512static struct throtl_grp *throtl_lookup_tg(struct throtl_data *td,
513                       struct blkcg *blkcg)
514{
515    /*
516     * This is the common case when there are no blkcgs. Avoid lookup
517     * in this case
518     */
519    if (blkcg == &blkcg_root)
520        return td_root_tg(td);
521
522    return blkg_to_tg(blkg_lookup(blkcg, td->queue));
523}
524
525static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
526                          struct blkcg *blkcg)
527{
528    struct request_queue *q = td->queue;
529    struct throtl_grp *tg = NULL;
530
531    /*
532     * This is the common case when there are no blkcgs. Avoid lookup
533     * in this case
534     */
535    if (blkcg == &blkcg_root) {
536        tg = td_root_tg(td);
537    } else {
538        struct blkcg_gq *blkg;
539
540        blkg = blkg_lookup_create(blkcg, q);
541
542        /* if %NULL and @q is alive, fall back to root_tg */
543        if (!IS_ERR(blkg))
544            tg = blkg_to_tg(blkg);
545        else if (!blk_queue_dying(q))
546            tg = td_root_tg(td);
547    }
548
549    return tg;
550}
551
552static struct throtl_grp *
553throtl_rb_first(struct throtl_service_queue *parent_sq)
554{
555    /* Service tree is empty */
556    if (!parent_sq->nr_pending)
557        return NULL;
558
559    if (!parent_sq->first_pending)
560        parent_sq->first_pending = rb_first(&parent_sq->pending_tree);
561
562    if (parent_sq->first_pending)
563        return rb_entry_tg(parent_sq->first_pending);
564
565    return NULL;
566}
567
568static void rb_erase_init(struct rb_node *n, struct rb_root *root)
569{
570    rb_erase(n, root);
571    RB_CLEAR_NODE(n);
572}
573
574static void throtl_rb_erase(struct rb_node *n,
575                struct throtl_service_queue *parent_sq)
576{
577    if (parent_sq->first_pending == n)
578        parent_sq->first_pending = NULL;
579    rb_erase_init(n, &parent_sq->pending_tree);
580    --parent_sq->nr_pending;
581}
582
583static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
584{
585    struct throtl_grp *tg;
586
587    tg = throtl_rb_first(parent_sq);
588    if (!tg)
589        return;
590
591    parent_sq->first_pending_disptime = tg->disptime;
592}
593
594static void tg_service_queue_add(struct throtl_grp *tg)
595{
596    struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
597    struct rb_node **node = &parent_sq->pending_tree.rb_node;
598    struct rb_node *parent = NULL;
599    struct throtl_grp *__tg;
600    unsigned long key = tg->disptime;
601    int left = 1;
602
603    while (*node != NULL) {
604        parent = *node;
605        __tg = rb_entry_tg(parent);
606
607        if (time_before(key, __tg->disptime))
608            node = &parent->rb_left;
609        else {
610            node = &parent->rb_right;
611            left = 0;
612        }
613    }
614
615    if (left)
616        parent_sq->first_pending = &tg->rb_node;
617
618    rb_link_node(&tg->rb_node, parent, node);
619    rb_insert_color(&tg->rb_node, &parent_sq->pending_tree);
620}
621
622static void __throtl_enqueue_tg(struct throtl_grp *tg)
623{
624    tg_service_queue_add(tg);
625    tg->flags |= THROTL_TG_PENDING;
626    tg->service_queue.parent_sq->nr_pending++;
627}
628
629static void throtl_enqueue_tg(struct throtl_grp *tg)
630{
631    if (!(tg->flags & THROTL_TG_PENDING))
632        __throtl_enqueue_tg(tg);
633}
634
635static void __throtl_dequeue_tg(struct throtl_grp *tg)
636{
637    throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
638    tg->flags &= ~THROTL_TG_PENDING;
639}
640
641static void throtl_dequeue_tg(struct throtl_grp *tg)
642{
643    if (tg->flags & THROTL_TG_PENDING)
644        __throtl_dequeue_tg(tg);
645}
646
647/* Call with queue lock held */
648static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
649                      unsigned long expires)
650{
651    mod_timer(&sq->pending_timer, expires);
652    throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
653           expires - jiffies, jiffies);
654}
655
656/**
657 * throtl_schedule_next_dispatch - schedule the next dispatch cycle
658 * @sq: the service_queue to schedule dispatch for
659 * @force: force scheduling
660 *
661 * Arm @sq->pending_timer so that the next dispatch cycle starts on the
662 * dispatch time of the first pending child. Returns %true if either timer
663 * is armed or there's no pending child left. %false if the current
664 * dispatch window is still open and the caller should continue
665 * dispatching.
666 *
667 * If @force is %true, the dispatch timer is always scheduled and this
668 * function is guaranteed to return %true. This is to be used when the
669 * caller can't dispatch itself and needs to invoke pending_timer
670 * unconditionally. Note that forced scheduling is likely to induce short
671 * delay before dispatch starts even if @sq->first_pending_disptime is not
672 * in the future and thus shouldn't be used in hot paths.
673 */
674static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
675                      bool force)
676{
677    /* any pending children left? */
678    if (!sq->nr_pending)
679        return true;
680
681    update_min_dispatch_time(sq);
682
683    /* is the next dispatch time in the future? */
684    if (force || time_after(sq->first_pending_disptime, jiffies)) {
685        throtl_schedule_pending_timer(sq, sq->first_pending_disptime);
686        return true;
687    }
688
689    /* tell the caller to continue dispatching */
690    return false;
691}
692
693static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
694        bool rw, unsigned long start)
695{
696    tg->bytes_disp[rw] = 0;
697    tg->io_disp[rw] = 0;
698
699    /*
700     * Previous slice has expired. We must have trimmed it after last
701     * bio dispatch. That means since start of last slice, we never used
702     * that bandwidth. Do try to make use of that bandwidth while giving
703     * credit.
704     */
705    if (time_after_eq(start, tg->slice_start[rw]))
706        tg->slice_start[rw] = start;
707
708    tg->slice_end[rw] = jiffies + throtl_slice;
709    throtl_log(&tg->service_queue,
710           "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
711           rw == READ ? 'R' : 'W', tg->slice_start[rw],
712           tg->slice_end[rw], jiffies);
713}
714
715static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
716{
717    tg->bytes_disp[rw] = 0;
718    tg->io_disp[rw] = 0;
719    tg->slice_start[rw] = jiffies;
720    tg->slice_end[rw] = jiffies + throtl_slice;
721    throtl_log(&tg->service_queue,
722           "[%c] new slice start=%lu end=%lu jiffies=%lu",
723           rw == READ ? 'R' : 'W', tg->slice_start[rw],
724           tg->slice_end[rw], jiffies);
725}
726
727static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
728                    unsigned long jiffy_end)
729{
730    tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
731}
732
733static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
734                       unsigned long jiffy_end)
735{
736    tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
737    throtl_log(&tg->service_queue,
738           "[%c] extend slice start=%lu end=%lu jiffies=%lu",
739           rw == READ ? 'R' : 'W', tg->slice_start[rw],
740           tg->slice_end[rw], jiffies);
741}
742
743/* Determine if previously allocated or extended slice is complete or not */
744static bool throtl_slice_used(struct throtl_grp *tg, bool rw)
745{
746    if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
747        return false;
748
749    return 1;
750}
751
752/* Trim the used slices and adjust slice start accordingly */
753static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
754{
755    unsigned long nr_slices, time_elapsed, io_trim;
756    u64 bytes_trim, tmp;
757
758    BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
759
760    /*
761     * If bps are unlimited (-1), then time slice don't get
762     * renewed. Don't try to trim the slice if slice is used. A new
763     * slice will start when appropriate.
764     */
765    if (throtl_slice_used(tg, rw))
766        return;
767
768    /*
769     * A bio has been dispatched. Also adjust slice_end. It might happen
770     * that initially cgroup limit was very low resulting in high
771     * slice_end, but later limit was bumped up and bio was dispached
772     * sooner, then we need to reduce slice_end. A high bogus slice_end
773     * is bad because it does not allow new slice to start.
774     */
775
776    throtl_set_slice_end(tg, rw, jiffies + throtl_slice);
777
778    time_elapsed = jiffies - tg->slice_start[rw];
779
780    nr_slices = time_elapsed / throtl_slice;
781
782    if (!nr_slices)
783        return;
784    tmp = tg->bps[rw] * throtl_slice * nr_slices;
785    do_div(tmp, HZ);
786    bytes_trim = tmp;
787
788    io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;
789
790    if (!bytes_trim && !io_trim)
791        return;
792
793    if (tg->bytes_disp[rw] >= bytes_trim)
794        tg->bytes_disp[rw] -= bytes_trim;
795    else
796        tg->bytes_disp[rw] = 0;
797
798    if (tg->io_disp[rw] >= io_trim)
799        tg->io_disp[rw] -= io_trim;
800    else
801        tg->io_disp[rw] = 0;
802
803    tg->slice_start[rw] += nr_slices * throtl_slice;
804
805    throtl_log(&tg->service_queue,
806           "[%c] trim slice nr=%lu bytes=%llu io=%lu start=%lu end=%lu jiffies=%lu",
807           rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
808           tg->slice_start[rw], tg->slice_end[rw], jiffies);
809}
810
811static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
812                  unsigned long *wait)
813{
814    bool rw = bio_data_dir(bio);
815    unsigned int io_allowed;
816    unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
817    u64 tmp;
818
819    jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
820
821    /* Slice has just started. Consider one slice interval */
822    if (!jiffy_elapsed)
823        jiffy_elapsed_rnd = throtl_slice;
824
825    jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
826
827    /*
828     * jiffy_elapsed_rnd should not be a big value as minimum iops can be
829     * 1 then at max jiffy elapsed should be equivalent of 1 second as we
830     * will allow dispatch after 1 second and after that slice should
831     * have been trimmed.
832     */
833
834    tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
835    do_div(tmp, HZ);
836
837    if (tmp > UINT_MAX)
838        io_allowed = UINT_MAX;
839    else
840        io_allowed = tmp;
841
842    if (tg->io_disp[rw] + 1 <= io_allowed) {
843        if (wait)
844            *wait = 0;
845        return true;
846    }
847
848    /* Calc approx time to dispatch */
849    jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1;
850
851    if (jiffy_wait > jiffy_elapsed)
852        jiffy_wait = jiffy_wait - jiffy_elapsed;
853    else
854        jiffy_wait = 1;
855
856    if (wait)
857        *wait = jiffy_wait;
858    return 0;
859}
860
861static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
862                 unsigned long *wait)
863{
864    bool rw = bio_data_dir(bio);
865    u64 bytes_allowed, extra_bytes, tmp;
866    unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
867
868    jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
869
870    /* Slice has just started. Consider one slice interval */
871    if (!jiffy_elapsed)
872        jiffy_elapsed_rnd = throtl_slice;
873
874    jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
875
876    tmp = tg->bps[rw] * jiffy_elapsed_rnd;
877    do_div(tmp, HZ);
878    bytes_allowed = tmp;
879
880    if (tg->bytes_disp[rw] + bio->bi_iter.bi_size <= bytes_allowed) {
881        if (wait)
882            *wait = 0;
883        return true;
884    }
885
886    /* Calc approx time to dispatch */
887    extra_bytes = tg->bytes_disp[rw] + bio->bi_iter.bi_size - bytes_allowed;
888    jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
889
890    if (!jiffy_wait)
891        jiffy_wait = 1;
892
893    /*
894     * This wait time is without taking into consideration the rounding
895     * up we did. Add that time also.
896     */
897    jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
898    if (wait)
899        *wait = jiffy_wait;
900    return 0;
901}
902
903/*
904 * Returns whether one can dispatch a bio or not. Also returns approx number
905 * of jiffies to wait before this bio is with-in IO rate and can be dispatched
906 */
907static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
908                unsigned long *wait)
909{
910    bool rw = bio_data_dir(bio);
911    unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
912
913    /*
914      * Currently whole state machine of group depends on first bio
915     * queued in the group bio list. So one should not be calling
916     * this function with a different bio if there are other bios
917     * queued.
918     */
919    BUG_ON(tg->service_queue.nr_queued[rw] &&
920           bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
921
922    /* If tg->bps = -1, then BW is unlimited */
923    if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
924        if (wait)
925            *wait = 0;
926        return true;
927    }
928
929    /*
930     * If previous slice expired, start a new one otherwise renew/extend
931     * existing slice to make sure it is at least throtl_slice interval
932     * long since now.
933     */
934    if (throtl_slice_used(tg, rw))
935        throtl_start_new_slice(tg, rw);
936    else {
937        if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
938            throtl_extend_slice(tg, rw, jiffies + throtl_slice);
939    }
940
941    if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
942        tg_with_in_iops_limit(tg, bio, &iops_wait)) {
943        if (wait)
944            *wait = 0;
945        return 1;
946    }
947
948    max_wait = max(bps_wait, iops_wait);
949
950    if (wait)
951        *wait = max_wait;
952
953    if (time_before(tg->slice_end[rw], jiffies + max_wait))
954        throtl_extend_slice(tg, rw, jiffies + max_wait);
955
956    return 0;
957}
958
959static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes,
960                     int rw)
961{
962    struct throtl_grp *tg = blkg_to_tg(blkg);
963    struct tg_stats_cpu *stats_cpu;
964    unsigned long flags;
965
966    /* If per cpu stats are not allocated yet, don't do any accounting. */
967    if (tg->stats_cpu == NULL)
968        return;
969
970    /*
971     * Disabling interrupts to provide mutual exclusion between two
972     * writes on same cpu. It probably is not needed for 64bit. Not
973     * optimizing that case yet.
974     */
975    local_irq_save(flags);
976
977    stats_cpu = this_cpu_ptr(tg->stats_cpu);
978
979    blkg_rwstat_add(&stats_cpu->serviced, rw, 1);
980    blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes);
981
982    local_irq_restore(flags);
983}
984
985static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
986{
987    bool rw = bio_data_dir(bio);
988
989    /* Charge the bio to the group */
990    tg->bytes_disp[rw] += bio->bi_iter.bi_size;
991    tg->io_disp[rw]++;
992
993    /*
994     * REQ_THROTTLED is used to prevent the same bio to be throttled
995     * more than once as a throttled bio will go through blk-throtl the
996     * second time when it eventually gets issued. Set it when a bio
997     * is being charged to a tg.
998     *
999     * Dispatch stats aren't recursive and each @bio should only be
1000     * accounted by the @tg it was originally associated with. Let's
1001     * update the stats when setting REQ_THROTTLED for the first time
1002     * which is guaranteed to be for the @bio's original tg.
1003     */
1004    if (!(bio->bi_rw & REQ_THROTTLED)) {
1005        bio->bi_rw |= REQ_THROTTLED;
1006        throtl_update_dispatch_stats(tg_to_blkg(tg),
1007                         bio->bi_iter.bi_size, bio->bi_rw);
1008    }
1009}
1010
1011/**
1012 * throtl_add_bio_tg - add a bio to the specified throtl_grp
1013 * @bio: bio to add
1014 * @qn: qnode to use
1015 * @tg: the target throtl_grp
1016 *
1017 * Add @bio to @tg's service_queue using @qn. If @qn is not specified,
1018 * tg->qnode_on_self[] is used.
1019 */
1020static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
1021                  struct throtl_grp *tg)
1022{
1023    struct throtl_service_queue *sq = &tg->service_queue;
1024    bool rw = bio_data_dir(bio);
1025
1026    if (!qn)
1027        qn = &tg->qnode_on_self[rw];
1028
1029    /*
1030     * If @tg doesn't currently have any bios queued in the same
1031     * direction, queueing @bio can change when @tg should be
1032     * dispatched. Mark that @tg was empty. This is automatically
1033     * cleaered on the next tg_update_disptime().
1034     */
1035    if (!sq->nr_queued[rw])
1036        tg->flags |= THROTL_TG_WAS_EMPTY;
1037
1038    throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
1039
1040    sq->nr_queued[rw]++;
1041    throtl_enqueue_tg(tg);
1042}
1043
1044static void tg_update_disptime(struct throtl_grp *tg)
1045{
1046    struct throtl_service_queue *sq = &tg->service_queue;
1047    unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
1048    struct bio *bio;
1049
1050    if ((bio = throtl_peek_queued(&sq->queued[READ])))
1051        tg_may_dispatch(tg, bio, &read_wait);
1052
1053    if ((bio = throtl_peek_queued(&sq->queued[WRITE])))
1054        tg_may_dispatch(tg, bio, &write_wait);
1055
1056    min_wait = min(read_wait, write_wait);
1057    disptime = jiffies + min_wait;
1058
1059    /* Update dispatch time */
1060    throtl_dequeue_tg(tg);
1061    tg->disptime = disptime;
1062    throtl_enqueue_tg(tg);
1063
1064    /* see throtl_add_bio_tg() */
1065    tg->flags &= ~THROTL_TG_WAS_EMPTY;
1066}
1067
1068static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
1069                    struct throtl_grp *parent_tg, bool rw)
1070{
1071    if (throtl_slice_used(parent_tg, rw)) {
1072        throtl_start_new_slice_with_credit(parent_tg, rw,
1073                child_tg->slice_start[rw]);
1074    }
1075
1076}
1077
1078static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
1079{
1080    struct throtl_service_queue *sq = &tg->service_queue;
1081    struct throtl_service_queue *parent_sq = sq->parent_sq;
1082    struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
1083    struct throtl_grp *tg_to_put = NULL;
1084    struct bio *bio;
1085
1086    /*
1087     * @bio is being transferred from @tg to @parent_sq. Popping a bio
1088     * from @tg may put its reference and @parent_sq might end up
1089     * getting released prematurely. Remember the tg to put and put it
1090     * after @bio is transferred to @parent_sq.
1091     */
1092    bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
1093    sq->nr_queued[rw]--;
1094
1095    throtl_charge_bio(tg, bio);
1096
1097    /*
1098     * If our parent is another tg, we just need to transfer @bio to
1099     * the parent using throtl_add_bio_tg(). If our parent is
1100     * @td->service_queue, @bio is ready to be issued. Put it on its
1101     * bio_lists[] and decrease total number queued. The caller is
1102     * responsible for issuing these bios.
1103     */
1104    if (parent_tg) {
1105        throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
1106        start_parent_slice_with_credit(tg, parent_tg, rw);
1107    } else {
1108        throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
1109                     &parent_sq->queued[rw]);
1110        BUG_ON(tg->td->nr_queued[rw] <= 0);
1111        tg->td->nr_queued[rw]--;
1112    }
1113
1114    throtl_trim_slice(tg, rw);
1115
1116    if (tg_to_put)
1117        blkg_put(tg_to_blkg(tg_to_put));
1118}
1119
1120static int throtl_dispatch_tg(struct throtl_grp *tg)
1121{
1122    struct throtl_service_queue *sq = &tg->service_queue;
1123    unsigned int nr_reads = 0, nr_writes = 0;
1124    unsigned int max_nr_reads = throtl_grp_quantum*3/4;
1125    unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
1126    struct bio *bio;
1127
1128    /* Try to dispatch 75% READS and 25% WRITES */
1129
1130    while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
1131           tg_may_dispatch(tg, bio, NULL)) {
1132
1133        tg_dispatch_one_bio(tg, bio_data_dir(bio));
1134        nr_reads++;
1135
1136        if (nr_reads >= max_nr_reads)
1137            break;
1138    }
1139
1140    while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
1141           tg_may_dispatch(tg, bio, NULL)) {
1142
1143        tg_dispatch_one_bio(tg, bio_data_dir(bio));
1144        nr_writes++;
1145
1146        if (nr_writes >= max_nr_writes)
1147            break;
1148    }
1149
1150    return nr_reads + nr_writes;
1151}
1152
1153static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
1154{
1155    unsigned int nr_disp = 0;
1156
1157    while (1) {
1158        struct throtl_grp *tg = throtl_rb_first(parent_sq);
1159        struct throtl_service_queue *sq = &tg->service_queue;
1160
1161        if (!tg)
1162            break;
1163
1164        if (time_before(jiffies, tg->disptime))
1165            break;
1166
1167        throtl_dequeue_tg(tg);
1168
1169        nr_disp += throtl_dispatch_tg(tg);
1170
1171        if (sq->nr_queued[0] || sq->nr_queued[1])
1172            tg_update_disptime(tg);
1173
1174        if (nr_disp >= throtl_quantum)
1175            break;
1176    }
1177
1178    return nr_disp;
1179}
1180
1181/**
1182 * throtl_pending_timer_fn - timer function for service_queue->pending_timer
1183 * @arg: the throtl_service_queue being serviced
1184 *
1185 * This timer is armed when a child throtl_grp with active bio's become
1186 * pending and queued on the service_queue's pending_tree and expires when
1187 * the first child throtl_grp should be dispatched. This function
1188 * dispatches bio's from the children throtl_grps to the parent
1189 * service_queue.
1190 *
1191 * If the parent's parent is another throtl_grp, dispatching is propagated
1192 * by either arming its pending_timer or repeating dispatch directly. If
1193 * the top-level service_tree is reached, throtl_data->dispatch_work is
1194 * kicked so that the ready bio's are issued.
1195 */
1196static void throtl_pending_timer_fn(unsigned long arg)
1197{
1198    struct throtl_service_queue *sq = (void *)arg;
1199    struct throtl_grp *tg = sq_to_tg(sq);
1200    struct throtl_data *td = sq_to_td(sq);
1201    struct request_queue *q = td->queue;
1202    struct throtl_service_queue *parent_sq;
1203    bool dispatched;
1204    int ret;
1205
1206    spin_lock_irq(q->queue_lock);
1207again:
1208    parent_sq = sq->parent_sq;
1209    dispatched = false;
1210
1211    while (true) {
1212        throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
1213               sq->nr_queued[READ] + sq->nr_queued[WRITE],
1214               sq->nr_queued[READ], sq->nr_queued[WRITE]);
1215
1216        ret = throtl_select_dispatch(sq);
1217        if (ret) {
1218            throtl_log(sq, "bios disp=%u", ret);
1219            dispatched = true;
1220        }
1221
1222        if (throtl_schedule_next_dispatch(sq, false))
1223            break;
1224
1225        /* this dispatch windows is still open, relax and repeat */
1226        spin_unlock_irq(q->queue_lock);
1227        cpu_relax();
1228        spin_lock_irq(q->queue_lock);
1229    }
1230
1231    if (!dispatched)
1232        goto out_unlock;
1233
1234    if (parent_sq) {
1235        /* @parent_sq is another throl_grp, propagate dispatch */
1236        if (tg->flags & THROTL_TG_WAS_EMPTY) {
1237            tg_update_disptime(tg);
1238            if (!throtl_schedule_next_dispatch(parent_sq, false)) {
1239                /* window is already open, repeat dispatching */
1240                sq = parent_sq;
1241                tg = sq_to_tg(sq);
1242                goto again;
1243            }
1244        }
1245    } else {
1246        /* reached the top-level, queue issueing */
1247        queue_work(kthrotld_workqueue, &td->dispatch_work);
1248    }
1249out_unlock:
1250    spin_unlock_irq(q->queue_lock);
1251}
1252
1253/**
1254 * blk_throtl_dispatch_work_fn - work function for throtl_data->dispatch_work
1255 * @work: work item being executed
1256 *
1257 * This function is queued for execution when bio's reach the bio_lists[]
1258 * of throtl_data->service_queue. Those bio's are ready and issued by this
1259 * function.
1260 */
1261static void blk_throtl_dispatch_work_fn(struct work_struct *work)
1262{
1263    struct throtl_data *td = container_of(work, struct throtl_data,
1264                          dispatch_work);
1265    struct throtl_service_queue *td_sq = &td->service_queue;
1266    struct request_queue *q = td->queue;
1267    struct bio_list bio_list_on_stack;
1268    struct bio *bio;
1269    struct blk_plug plug;
1270    int rw;
1271
1272    bio_list_init(&bio_list_on_stack);
1273
1274    spin_lock_irq(q->queue_lock);
1275    for (rw = READ; rw <= WRITE; rw++)
1276        while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
1277            bio_list_add(&bio_list_on_stack, bio);
1278    spin_unlock_irq(q->queue_lock);
1279
1280    if (!bio_list_empty(&bio_list_on_stack)) {
1281        blk_start_plug(&plug);
1282        while((bio = bio_list_pop(&bio_list_on_stack)))
1283            generic_make_request(bio);
1284        blk_finish_plug(&plug);
1285    }
1286}
1287
1288static u64 tg_prfill_cpu_rwstat(struct seq_file *sf,
1289                struct blkg_policy_data *pd, int off)
1290{
1291    struct throtl_grp *tg = pd_to_tg(pd);
1292    struct blkg_rwstat rwstat = { }, tmp;
1293    int i, cpu;
1294
1295    for_each_possible_cpu(cpu) {
1296        struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);
1297
1298        tmp = blkg_rwstat_read((void *)sc + off);
1299        for (i = 0; i < BLKG_RWSTAT_NR; i++)
1300            rwstat.cnt[i] += tmp.cnt[i];
1301    }
1302
1303    return __blkg_prfill_rwstat(sf, pd, &rwstat);
1304}
1305
1306static int tg_print_cpu_rwstat(struct seq_file *sf, void *v)
1307{
1308    blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_cpu_rwstat,
1309              &blkcg_policy_throtl, seq_cft(sf)->private, true);
1310    return 0;
1311}
1312
1313static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
1314                  int off)
1315{
1316    struct throtl_grp *tg = pd_to_tg(pd);
1317    u64 v = *(u64 *)((void *)tg + off);
1318
1319    if (v == -1)
1320        return 0;
1321    return __blkg_prfill_u64(sf, pd, v);
1322}
1323
1324static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
1325                   int off)
1326{
1327    struct throtl_grp *tg = pd_to_tg(pd);
1328    unsigned int v = *(unsigned int *)((void *)tg + off);
1329
1330    if (v == -1)
1331        return 0;
1332    return __blkg_prfill_u64(sf, pd, v);
1333}
1334
1335static int tg_print_conf_u64(struct seq_file *sf, void *v)
1336{
1337    blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_u64,
1338              &blkcg_policy_throtl, seq_cft(sf)->private, false);
1339    return 0;
1340}
1341
1342static int tg_print_conf_uint(struct seq_file *sf, void *v)
1343{
1344    blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_uint,
1345              &blkcg_policy_throtl, seq_cft(sf)->private, false);
1346    return 0;
1347}
1348
1349static ssize_t tg_set_conf(struct kernfs_open_file *of,
1350               char *buf, size_t nbytes, loff_t off, bool is_u64)
1351{
1352    struct blkcg *blkcg = css_to_blkcg(of_css(of));
1353    struct blkg_conf_ctx ctx;
1354    struct throtl_grp *tg;
1355    struct throtl_service_queue *sq;
1356    struct blkcg_gq *blkg;
1357    struct cgroup_subsys_state *pos_css;
1358    int ret;
1359
1360    ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
1361    if (ret)
1362        return ret;
1363
1364    tg = blkg_to_tg(ctx.blkg);
1365    sq = &tg->service_queue;
1366
1367    if (!ctx.v)
1368        ctx.v = -1;
1369
1370    if (is_u64)
1371        *(u64 *)((void *)tg + of_cft(of)->private) = ctx.v;
1372    else
1373        *(unsigned int *)((void *)tg + of_cft(of)->private) = ctx.v;
1374
1375    throtl_log(&tg->service_queue,
1376           "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
1377           tg->bps[READ], tg->bps[WRITE],
1378           tg->iops[READ], tg->iops[WRITE]);
1379
1380    /*
1381     * Update has_rules[] flags for the updated tg's subtree. A tg is
1382     * considered to have rules if either the tg itself or any of its
1383     * ancestors has rules. This identifies groups without any
1384     * restrictions in the whole hierarchy and allows them to bypass
1385     * blk-throttle.
1386     */
1387    blkg_for_each_descendant_pre(blkg, pos_css, ctx.blkg)
1388        tg_update_has_rules(blkg_to_tg(blkg));
1389
1390    /*
1391     * We're already holding queue_lock and know @tg is valid. Let's
1392     * apply the new config directly.
1393     *
1394     * Restart the slices for both READ and WRITES. It might happen
1395     * that a group's limit are dropped suddenly and we don't want to
1396     * account recently dispatched IO with new low rate.
1397     */
1398    throtl_start_new_slice(tg, 0);
1399    throtl_start_new_slice(tg, 1);
1400
1401    if (tg->flags & THROTL_TG_PENDING) {
1402        tg_update_disptime(tg);
1403        throtl_schedule_next_dispatch(sq->parent_sq, true);
1404    }
1405
1406    blkg_conf_finish(&ctx);
1407    return nbytes;
1408}
1409
1410static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
1411                   char *buf, size_t nbytes, loff_t off)
1412{
1413    return tg_set_conf(of, buf, nbytes, off, true);
1414}
1415
1416static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
1417                char *buf, size_t nbytes, loff_t off)
1418{
1419    return tg_set_conf(of, buf, nbytes, off, false);
1420}
1421
1422static struct cftype throtl_files[] = {
1423    {
1424        .name = "throttle.read_bps_device",
1425        .private = offsetof(struct throtl_grp, bps[READ]),
1426        .seq_show = tg_print_conf_u64,
1427        .write = tg_set_conf_u64,
1428    },
1429    {
1430        .name = "throttle.write_bps_device",
1431        .private = offsetof(struct throtl_grp, bps[WRITE]),
1432        .seq_show = tg_print_conf_u64,
1433        .write = tg_set_conf_u64,
1434    },
1435    {
1436        .name = "throttle.read_iops_device",
1437        .private = offsetof(struct throtl_grp, iops[READ]),
1438        .seq_show = tg_print_conf_uint,
1439        .write = tg_set_conf_uint,
1440    },
1441    {
1442        .name = "throttle.write_iops_device",
1443        .private = offsetof(struct throtl_grp, iops[WRITE]),
1444        .seq_show = tg_print_conf_uint,
1445        .write = tg_set_conf_uint,
1446    },
1447    {
1448        .name = "throttle.io_service_bytes",
1449        .private = offsetof(struct tg_stats_cpu, service_bytes),
1450        .seq_show = tg_print_cpu_rwstat,
1451    },
1452    {
1453        .name = "throttle.io_serviced",
1454        .private = offsetof(struct tg_stats_cpu, serviced),
1455        .seq_show = tg_print_cpu_rwstat,
1456    },
1457    { } /* terminate */
1458};
1459
1460static void throtl_shutdown_wq(struct request_queue *q)
1461{
1462    struct throtl_data *td = q->td;
1463
1464    cancel_work_sync(&td->dispatch_work);
1465}
1466
1467static struct blkcg_policy blkcg_policy_throtl = {
1468    .pd_size = sizeof(struct throtl_grp),
1469    .cftypes = throtl_files,
1470
1471    .pd_init_fn = throtl_pd_init,
1472    .pd_online_fn = throtl_pd_online,
1473    .pd_exit_fn = throtl_pd_exit,
1474    .pd_reset_stats_fn = throtl_pd_reset_stats,
1475};
1476
1477bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
1478{
1479    struct throtl_data *td = q->td;
1480    struct throtl_qnode *qn = NULL;
1481    struct throtl_grp *tg;
1482    struct throtl_service_queue *sq;
1483    bool rw = bio_data_dir(bio);
1484    struct blkcg *blkcg;
1485    bool throttled = false;
1486
1487    /* see throtl_charge_bio() */
1488    if (bio->bi_rw & REQ_THROTTLED)
1489        goto out;
1490
1491    /*
1492     * A throtl_grp pointer retrieved under rcu can be used to access
1493     * basic fields like stats and io rates. If a group has no rules,
1494     * just update the dispatch stats in lockless manner and return.
1495     */
1496    rcu_read_lock();
1497    blkcg = bio_blkcg(bio);
1498    tg = throtl_lookup_tg(td, blkcg);
1499    if (tg) {
1500        if (!tg->has_rules[rw]) {
1501            throtl_update_dispatch_stats(tg_to_blkg(tg),
1502                    bio->bi_iter.bi_size, bio->bi_rw);
1503            goto out_unlock_rcu;
1504        }
1505    }
1506
1507    /*
1508     * Either group has not been allocated yet or it is not an unlimited
1509     * IO group
1510     */
1511    spin_lock_irq(q->queue_lock);
1512    tg = throtl_lookup_create_tg(td, blkcg);
1513    if (unlikely(!tg))
1514        goto out_unlock;
1515
1516    sq = &tg->service_queue;
1517
1518    while (true) {
1519        /* throtl is FIFO - if bios are already queued, should queue */
1520        if (sq->nr_queued[rw])
1521            break;
1522
1523        /* if above limits, break to queue */
1524        if (!tg_may_dispatch(tg, bio, NULL))
1525            break;
1526
1527        /* within limits, let's charge and dispatch directly */
1528        throtl_charge_bio(tg, bio);
1529
1530        /*
1531         * We need to trim slice even when bios are not being queued
1532         * otherwise it might happen that a bio is not queued for
1533         * a long time and slice keeps on extending and trim is not
1534         * called for a long time. Now if limits are reduced suddenly
1535         * we take into account all the IO dispatched so far at new
1536         * low rate and * newly queued IO gets a really long dispatch
1537         * time.
1538         *
1539         * So keep on trimming slice even if bio is not queued.
1540         */
1541        throtl_trim_slice(tg, rw);
1542
1543        /*
1544         * @bio passed through this layer without being throttled.
1545         * Climb up the ladder. If we''re already at the top, it
1546         * can be executed directly.
1547         */
1548        qn = &tg->qnode_on_parent[rw];
1549        sq = sq->parent_sq;
1550        tg = sq_to_tg(sq);
1551        if (!tg)
1552            goto out_unlock;
1553    }
1554
1555    /* out-of-limit, queue to @tg */
1556    throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
1557           rw == READ ? 'R' : 'W',
1558           tg->bytes_disp[rw], bio->bi_iter.bi_size, tg->bps[rw],
1559           tg->io_disp[rw], tg->iops[rw],
1560           sq->nr_queued[READ], sq->nr_queued[WRITE]);
1561
1562    bio_associate_current(bio);
1563    tg->td->nr_queued[rw]++;
1564    throtl_add_bio_tg(bio, qn, tg);
1565    throttled = true;
1566
1567    /*
1568     * Update @tg's dispatch time and force schedule dispatch if @tg
1569     * was empty before @bio. The forced scheduling isn't likely to
1570     * cause undue delay as @bio is likely to be dispatched directly if
1571     * its @tg's disptime is not in the future.
1572     */
1573    if (tg->flags & THROTL_TG_WAS_EMPTY) {
1574        tg_update_disptime(tg);
1575        throtl_schedule_next_dispatch(tg->service_queue.parent_sq, true);
1576    }
1577
1578out_unlock:
1579    spin_unlock_irq(q->queue_lock);
1580out_unlock_rcu:
1581    rcu_read_unlock();
1582out:
1583    /*
1584     * As multiple blk-throtls may stack in the same issue path, we
1585     * don't want bios to leave with the flag set. Clear the flag if
1586     * being issued.
1587     */
1588    if (!throttled)
1589        bio->bi_rw &= ~REQ_THROTTLED;
1590    return throttled;
1591}
1592
1593/*
1594 * Dispatch all bios from all children tg's queued on @parent_sq. On
1595 * return, @parent_sq is guaranteed to not have any active children tg's
1596 * and all bios from previously active tg's are on @parent_sq->bio_lists[].
1597 */
1598static void tg_drain_bios(struct throtl_service_queue *parent_sq)
1599{
1600    struct throtl_grp *tg;
1601
1602    while ((tg = throtl_rb_first(parent_sq))) {
1603        struct throtl_service_queue *sq = &tg->service_queue;
1604        struct bio *bio;
1605
1606        throtl_dequeue_tg(tg);
1607
1608        while ((bio = throtl_peek_queued(&sq->queued[READ])))
1609            tg_dispatch_one_bio(tg, bio_data_dir(bio));
1610        while ((bio = throtl_peek_queued(&sq->queued[WRITE])))
1611            tg_dispatch_one_bio(tg, bio_data_dir(bio));
1612    }
1613}
1614
1615/**
1616 * blk_throtl_drain - drain throttled bios
1617 * @q: request_queue to drain throttled bios for
1618 *
1619 * Dispatch all currently throttled bios on @q through ->make_request_fn().
1620 */
1621void blk_throtl_drain(struct request_queue *q)
1622    __releases(q->queue_lock) __acquires(q->queue_lock)
1623{
1624    struct throtl_data *td = q->td;
1625    struct blkcg_gq *blkg;
1626    struct cgroup_subsys_state *pos_css;
1627    struct bio *bio;
1628    int rw;
1629
1630    queue_lockdep_assert_held(q);
1631    rcu_read_lock();
1632
1633    /*
1634     * Drain each tg while doing post-order walk on the blkg tree, so
1635     * that all bios are propagated to td->service_queue. It'd be
1636     * better to walk service_queue tree directly but blkg walk is
1637     * easier.
1638     */
1639    blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
1640        tg_drain_bios(&blkg_to_tg(blkg)->service_queue);
1641
1642    /* finally, transfer bios from top-level tg's into the td */
1643    tg_drain_bios(&td->service_queue);
1644
1645    rcu_read_unlock();
1646    spin_unlock_irq(q->queue_lock);
1647
1648    /* all bios now should be in td->service_queue, issue them */
1649    for (rw = READ; rw <= WRITE; rw++)
1650        while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
1651                        NULL)))
1652            generic_make_request(bio);
1653
1654    spin_lock_irq(q->queue_lock);
1655}
1656
1657int blk_throtl_init(struct request_queue *q)
1658{
1659    struct throtl_data *td;
1660    int ret;
1661
1662    td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
1663    if (!td)
1664        return -ENOMEM;
1665
1666    INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);
1667    throtl_service_queue_init(&td->service_queue, NULL);
1668
1669    q->td = td;
1670    td->queue = q;
1671
1672    /* activate policy */
1673    ret = blkcg_activate_policy(q, &blkcg_policy_throtl);
1674    if (ret)
1675        kfree(td);
1676    return ret;
1677}
1678
1679void blk_throtl_exit(struct request_queue *q)
1680{
1681    BUG_ON(!q->td);
1682    throtl_shutdown_wq(q);
1683    blkcg_deactivate_policy(q, &blkcg_policy_throtl);
1684    kfree(q->td);
1685}
1686
1687static int __init throtl_init(void)
1688{
1689    kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
1690    if (!kthrotld_workqueue)
1691        panic("Failed to create kthrotld\n");
1692
1693    return blkcg_policy_register(&blkcg_policy_throtl);
1694}
1695
1696module_init(throtl_init);
1697

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