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
14/* Max dispatch from a group in 1 round */
15static int throtl_grp_quantum = 8;
16
17/* Total max dispatch from all groups in one round */
18static int throtl_quantum = 32;
19
20/* Throttling is performed over 100ms slice and after that slice is renewed */
21static unsigned long throtl_slice = HZ/10; /* 100 ms */
22
23struct throtl_rb_root {
24    struct rb_root rb;
25    struct rb_node *left;
26    unsigned int count;
27    unsigned long min_disptime;
28};
29
30#define THROTL_RB_ROOT (struct throtl_rb_root) { .rb = RB_ROOT, .left = NULL, \
31            .count = 0, .min_disptime = 0}
32
33#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)
34
35struct throtl_grp {
36    /* List of throtl groups on the request queue*/
37    struct hlist_node tg_node;
38
39    /* active throtl group service_tree member */
40    struct rb_node rb_node;
41
42    /*
43     * Dispatch time in jiffies. This is the estimated time when group
44     * will unthrottle and is ready to dispatch more bio. It is used as
45     * key to sort active groups in service tree.
46     */
47    unsigned long disptime;
48
49    struct blkio_group blkg;
50    atomic_t ref;
51    unsigned int flags;
52
53    /* Two lists for READ and WRITE */
54    struct bio_list bio_lists[2];
55
56    /* Number of queued bios on READ and WRITE lists */
57    unsigned int nr_queued[2];
58
59    /* bytes per second rate limits */
60    uint64_t bps[2];
61
62    /* IOPS limits */
63    unsigned int iops[2];
64
65    /* Number of bytes disptached in current slice */
66    uint64_t bytes_disp[2];
67    /* Number of bio's dispatched in current slice */
68    unsigned int io_disp[2];
69
70    /* When did we start a new slice */
71    unsigned long slice_start[2];
72    unsigned long slice_end[2];
73
74    /* Some throttle limits got updated for the group */
75    bool limits_changed;
76};
77
78struct throtl_data
79{
80    /* List of throtl groups */
81    struct hlist_head tg_list;
82
83    /* service tree for active throtl groups */
84    struct throtl_rb_root tg_service_tree;
85
86    struct throtl_grp root_tg;
87    struct request_queue *queue;
88
89    /* Total Number of queued bios on READ and WRITE lists */
90    unsigned int nr_queued[2];
91
92    /*
93     * number of total undestroyed groups
94     */
95    unsigned int nr_undestroyed_grps;
96
97    /* Work for dispatching throttled bios */
98    struct delayed_work throtl_work;
99
100    atomic_t limits_changed;
101};
102
103enum tg_state_flags {
104    THROTL_TG_FLAG_on_rr = 0, /* on round-robin busy list */
105};
106
107#define THROTL_TG_FNS(name) \
108static inline void throtl_mark_tg_##name(struct throtl_grp *tg) \
109{ \
110    (tg)->flags |= (1 << THROTL_TG_FLAG_##name); \
111} \
112static inline void throtl_clear_tg_##name(struct throtl_grp *tg) \
113{ \
114    (tg)->flags &= ~(1 << THROTL_TG_FLAG_##name); \
115} \
116static inline int throtl_tg_##name(const struct throtl_grp *tg) \
117{ \
118    return ((tg)->flags & (1 << THROTL_TG_FLAG_##name)) != 0; \
119}
120
121THROTL_TG_FNS(on_rr);
122
123#define throtl_log_tg(td, tg, fmt, args...) \
124    blk_add_trace_msg((td)->queue, "throtl %s " fmt, \
125                blkg_path(&(tg)->blkg), ##args); \
126
127#define throtl_log(td, fmt, args...) \
128    blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)
129
130static inline struct throtl_grp *tg_of_blkg(struct blkio_group *blkg)
131{
132    if (blkg)
133        return container_of(blkg, struct throtl_grp, blkg);
134
135    return NULL;
136}
137
138static inline int total_nr_queued(struct throtl_data *td)
139{
140    return (td->nr_queued[0] + td->nr_queued[1]);
141}
142
143static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
144{
145    atomic_inc(&tg->ref);
146    return tg;
147}
148
149static void throtl_put_tg(struct throtl_grp *tg)
150{
151    BUG_ON(atomic_read(&tg->ref) <= 0);
152    if (!atomic_dec_and_test(&tg->ref))
153        return;
154    kfree(tg);
155}
156
157static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
158            struct cgroup *cgroup)
159{
160    struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
161    struct throtl_grp *tg = NULL;
162    void *key = td;
163    struct backing_dev_info *bdi = &td->queue->backing_dev_info;
164    unsigned int major, minor;
165
166    /*
167     * TODO: Speed up blkiocg_lookup_group() by maintaining a radix
168     * tree of blkg (instead of traversing through hash list all
169     * the time.
170     */
171    tg = tg_of_blkg(blkiocg_lookup_group(blkcg, key));
172
173    /* Fill in device details for root group */
174    if (tg && !tg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
175        sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
176        tg->blkg.dev = MKDEV(major, minor);
177        goto done;
178    }
179
180    if (tg)
181        goto done;
182
183    tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
184    if (!tg)
185        goto done;
186
187    INIT_HLIST_NODE(&tg->tg_node);
188    RB_CLEAR_NODE(&tg->rb_node);
189    bio_list_init(&tg->bio_lists[0]);
190    bio_list_init(&tg->bio_lists[1]);
191
192    /*
193     * Take the initial reference that will be released on destroy
194     * This can be thought of a joint reference by cgroup and
195     * request queue which will be dropped by either request queue
196     * exit or cgroup deletion path depending on who is exiting first.
197     */
198    atomic_set(&tg->ref, 1);
199
200    /* Add group onto cgroup list */
201    sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
202    blkiocg_add_blkio_group(blkcg, &tg->blkg, (void *)td,
203                MKDEV(major, minor), BLKIO_POLICY_THROTL);
204
205    tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
206    tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
207    tg->iops[READ] = blkcg_get_read_iops(blkcg, tg->blkg.dev);
208    tg->iops[WRITE] = blkcg_get_write_iops(blkcg, tg->blkg.dev);
209
210    hlist_add_head(&tg->tg_node, &td->tg_list);
211    td->nr_undestroyed_grps++;
212done:
213    return tg;
214}
215
216static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
217{
218    struct cgroup *cgroup;
219    struct throtl_grp *tg = NULL;
220
221    rcu_read_lock();
222    cgroup = task_cgroup(current, blkio_subsys_id);
223    tg = throtl_find_alloc_tg(td, cgroup);
224    if (!tg)
225        tg = &td->root_tg;
226    rcu_read_unlock();
227    return tg;
228}
229
230static struct throtl_grp *throtl_rb_first(struct throtl_rb_root *root)
231{
232    /* Service tree is empty */
233    if (!root->count)
234        return NULL;
235
236    if (!root->left)
237        root->left = rb_first(&root->rb);
238
239    if (root->left)
240        return rb_entry_tg(root->left);
241
242    return NULL;
243}
244
245static void rb_erase_init(struct rb_node *n, struct rb_root *root)
246{
247    rb_erase(n, root);
248    RB_CLEAR_NODE(n);
249}
250
251static void throtl_rb_erase(struct rb_node *n, struct throtl_rb_root *root)
252{
253    if (root->left == n)
254        root->left = NULL;
255    rb_erase_init(n, &root->rb);
256    --root->count;
257}
258
259static void update_min_dispatch_time(struct throtl_rb_root *st)
260{
261    struct throtl_grp *tg;
262
263    tg = throtl_rb_first(st);
264    if (!tg)
265        return;
266
267    st->min_disptime = tg->disptime;
268}
269
270static void
271tg_service_tree_add(struct throtl_rb_root *st, struct throtl_grp *tg)
272{
273    struct rb_node **node = &st->rb.rb_node;
274    struct rb_node *parent = NULL;
275    struct throtl_grp *__tg;
276    unsigned long key = tg->disptime;
277    int left = 1;
278
279    while (*node != NULL) {
280        parent = *node;
281        __tg = rb_entry_tg(parent);
282
283        if (time_before(key, __tg->disptime))
284            node = &parent->rb_left;
285        else {
286            node = &parent->rb_right;
287            left = 0;
288        }
289    }
290
291    if (left)
292        st->left = &tg->rb_node;
293
294    rb_link_node(&tg->rb_node, parent, node);
295    rb_insert_color(&tg->rb_node, &st->rb);
296}
297
298static void __throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
299{
300    struct throtl_rb_root *st = &td->tg_service_tree;
301
302    tg_service_tree_add(st, tg);
303    throtl_mark_tg_on_rr(tg);
304    st->count++;
305}
306
307static void throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
308{
309    if (!throtl_tg_on_rr(tg))
310        __throtl_enqueue_tg(td, tg);
311}
312
313static void __throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
314{
315    throtl_rb_erase(&tg->rb_node, &td->tg_service_tree);
316    throtl_clear_tg_on_rr(tg);
317}
318
319static void throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
320{
321    if (throtl_tg_on_rr(tg))
322        __throtl_dequeue_tg(td, tg);
323}
324
325static void throtl_schedule_next_dispatch(struct throtl_data *td)
326{
327    struct throtl_rb_root *st = &td->tg_service_tree;
328
329    /*
330     * If there are more bios pending, schedule more work.
331     */
332    if (!total_nr_queued(td))
333        return;
334
335    BUG_ON(!st->count);
336
337    update_min_dispatch_time(st);
338
339    if (time_before_eq(st->min_disptime, jiffies))
340        throtl_schedule_delayed_work(td->queue, 0);
341    else
342        throtl_schedule_delayed_work(td->queue,
343                (st->min_disptime - jiffies));
344}
345
346static inline void
347throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
348{
349    tg->bytes_disp[rw] = 0;
350    tg->io_disp[rw] = 0;
351    tg->slice_start[rw] = jiffies;
352    tg->slice_end[rw] = jiffies + throtl_slice;
353    throtl_log_tg(td, tg, "[%c] new slice start=%lu end=%lu jiffies=%lu",
354            rw == READ ? 'R' : 'W', tg->slice_start[rw],
355            tg->slice_end[rw], jiffies);
356}
357
358static inline void throtl_set_slice_end(struct throtl_data *td,
359        struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
360{
361    tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
362}
363
364static inline void throtl_extend_slice(struct throtl_data *td,
365        struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
366{
367    tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
368    throtl_log_tg(td, tg, "[%c] extend slice start=%lu end=%lu jiffies=%lu",
369            rw == READ ? 'R' : 'W', tg->slice_start[rw],
370            tg->slice_end[rw], jiffies);
371}
372
373/* Determine if previously allocated or extended slice is complete or not */
374static bool
375throtl_slice_used(struct throtl_data *td, struct throtl_grp *tg, bool rw)
376{
377    if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
378        return 0;
379
380    return 1;
381}
382
383/* Trim the used slices and adjust slice start accordingly */
384static inline void
385throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
386{
387    unsigned long nr_slices, time_elapsed, io_trim;
388    u64 bytes_trim, tmp;
389
390    BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
391
392    /*
393     * If bps are unlimited (-1), then time slice don't get
394     * renewed. Don't try to trim the slice if slice is used. A new
395     * slice will start when appropriate.
396     */
397    if (throtl_slice_used(td, tg, rw))
398        return;
399
400    /*
401     * A bio has been dispatched. Also adjust slice_end. It might happen
402     * that initially cgroup limit was very low resulting in high
403     * slice_end, but later limit was bumped up and bio was dispached
404     * sooner, then we need to reduce slice_end. A high bogus slice_end
405     * is bad because it does not allow new slice to start.
406     */
407
408    throtl_set_slice_end(td, tg, rw, jiffies + throtl_slice);
409
410    time_elapsed = jiffies - tg->slice_start[rw];
411
412    nr_slices = time_elapsed / throtl_slice;
413
414    if (!nr_slices)
415        return;
416    tmp = tg->bps[rw] * throtl_slice * nr_slices;
417    do_div(tmp, HZ);
418    bytes_trim = tmp;
419
420    io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;
421
422    if (!bytes_trim && !io_trim)
423        return;
424
425    if (tg->bytes_disp[rw] >= bytes_trim)
426        tg->bytes_disp[rw] -= bytes_trim;
427    else
428        tg->bytes_disp[rw] = 0;
429
430    if (tg->io_disp[rw] >= io_trim)
431        tg->io_disp[rw] -= io_trim;
432    else
433        tg->io_disp[rw] = 0;
434
435    tg->slice_start[rw] += nr_slices * throtl_slice;
436
437    throtl_log_tg(td, tg, "[%c] trim slice nr=%lu bytes=%llu io=%lu"
438            " start=%lu end=%lu jiffies=%lu",
439            rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
440            tg->slice_start[rw], tg->slice_end[rw], jiffies);
441}
442
443static bool tg_with_in_iops_limit(struct throtl_data *td, struct throtl_grp *tg,
444        struct bio *bio, unsigned long *wait)
445{
446    bool rw = bio_data_dir(bio);
447    unsigned int io_allowed;
448    unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
449    u64 tmp;
450
451    jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
452
453    /* Slice has just started. Consider one slice interval */
454    if (!jiffy_elapsed)
455        jiffy_elapsed_rnd = throtl_slice;
456
457    jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
458
459    /*
460     * jiffy_elapsed_rnd should not be a big value as minimum iops can be
461     * 1 then at max jiffy elapsed should be equivalent of 1 second as we
462     * will allow dispatch after 1 second and after that slice should
463     * have been trimmed.
464     */
465
466    tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
467    do_div(tmp, HZ);
468
469    if (tmp > UINT_MAX)
470        io_allowed = UINT_MAX;
471    else
472        io_allowed = tmp;
473
474    if (tg->io_disp[rw] + 1 <= io_allowed) {
475        if (wait)
476            *wait = 0;
477        return 1;
478    }
479
480    /* Calc approx time to dispatch */
481    jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1;
482
483    if (jiffy_wait > jiffy_elapsed)
484        jiffy_wait = jiffy_wait - jiffy_elapsed;
485    else
486        jiffy_wait = 1;
487
488    if (wait)
489        *wait = jiffy_wait;
490    return 0;
491}
492
493static bool tg_with_in_bps_limit(struct throtl_data *td, struct throtl_grp *tg,
494        struct bio *bio, unsigned long *wait)
495{
496    bool rw = bio_data_dir(bio);
497    u64 bytes_allowed, extra_bytes, tmp;
498    unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
499
500    jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
501
502    /* Slice has just started. Consider one slice interval */
503    if (!jiffy_elapsed)
504        jiffy_elapsed_rnd = throtl_slice;
505
506    jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
507
508    tmp = tg->bps[rw] * jiffy_elapsed_rnd;
509    do_div(tmp, HZ);
510    bytes_allowed = tmp;
511
512    if (tg->bytes_disp[rw] + bio->bi_size <= bytes_allowed) {
513        if (wait)
514            *wait = 0;
515        return 1;
516    }
517
518    /* Calc approx time to dispatch */
519    extra_bytes = tg->bytes_disp[rw] + bio->bi_size - bytes_allowed;
520    jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
521
522    if (!jiffy_wait)
523        jiffy_wait = 1;
524
525    /*
526     * This wait time is without taking into consideration the rounding
527     * up we did. Add that time also.
528     */
529    jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
530    if (wait)
531        *wait = jiffy_wait;
532    return 0;
533}
534
535/*
536 * Returns whether one can dispatch a bio or not. Also returns approx number
537 * of jiffies to wait before this bio is with-in IO rate and can be dispatched
538 */
539static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
540                struct bio *bio, unsigned long *wait)
541{
542    bool rw = bio_data_dir(bio);
543    unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
544
545    /*
546      * Currently whole state machine of group depends on first bio
547     * queued in the group bio list. So one should not be calling
548     * this function with a different bio if there are other bios
549     * queued.
550     */
551    BUG_ON(tg->nr_queued[rw] && bio != bio_list_peek(&tg->bio_lists[rw]));
552
553    /* If tg->bps = -1, then BW is unlimited */
554    if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
555        if (wait)
556            *wait = 0;
557        return 1;
558    }
559
560    /*
561     * If previous slice expired, start a new one otherwise renew/extend
562     * existing slice to make sure it is at least throtl_slice interval
563     * long since now.
564     */
565    if (throtl_slice_used(td, tg, rw))
566        throtl_start_new_slice(td, tg, rw);
567    else {
568        if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
569            throtl_extend_slice(td, tg, rw, jiffies + throtl_slice);
570    }
571
572    if (tg_with_in_bps_limit(td, tg, bio, &bps_wait)
573        && tg_with_in_iops_limit(td, tg, bio, &iops_wait)) {
574        if (wait)
575            *wait = 0;
576        return 1;
577    }
578
579    max_wait = max(bps_wait, iops_wait);
580
581    if (wait)
582        *wait = max_wait;
583
584    if (time_before(tg->slice_end[rw], jiffies + max_wait))
585        throtl_extend_slice(td, tg, rw, jiffies + max_wait);
586
587    return 0;
588}
589
590static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
591{
592    bool rw = bio_data_dir(bio);
593    bool sync = bio->bi_rw & REQ_SYNC;
594
595    /* Charge the bio to the group */
596    tg->bytes_disp[rw] += bio->bi_size;
597    tg->io_disp[rw]++;
598
599    /*
600     * TODO: This will take blkg->stats_lock. Figure out a way
601     * to avoid this cost.
602     */
603    blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size, rw, sync);
604}
605
606static void throtl_add_bio_tg(struct throtl_data *td, struct throtl_grp *tg,
607            struct bio *bio)
608{
609    bool rw = bio_data_dir(bio);
610
611    bio_list_add(&tg->bio_lists[rw], bio);
612    /* Take a bio reference on tg */
613    throtl_ref_get_tg(tg);
614    tg->nr_queued[rw]++;
615    td->nr_queued[rw]++;
616    throtl_enqueue_tg(td, tg);
617}
618
619static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
620{
621    unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
622    struct bio *bio;
623
624    if ((bio = bio_list_peek(&tg->bio_lists[READ])))
625        tg_may_dispatch(td, tg, bio, &read_wait);
626
627    if ((bio = bio_list_peek(&tg->bio_lists[WRITE])))
628        tg_may_dispatch(td, tg, bio, &write_wait);
629
630    min_wait = min(read_wait, write_wait);
631    disptime = jiffies + min_wait;
632
633    /* Update dispatch time */
634    throtl_dequeue_tg(td, tg);
635    tg->disptime = disptime;
636    throtl_enqueue_tg(td, tg);
637}
638
639static void tg_dispatch_one_bio(struct throtl_data *td, struct throtl_grp *tg,
640                bool rw, struct bio_list *bl)
641{
642    struct bio *bio;
643
644    bio = bio_list_pop(&tg->bio_lists[rw]);
645    tg->nr_queued[rw]--;
646    /* Drop bio reference on tg */
647    throtl_put_tg(tg);
648
649    BUG_ON(td->nr_queued[rw] <= 0);
650    td->nr_queued[rw]--;
651
652    throtl_charge_bio(tg, bio);
653    bio_list_add(bl, bio);
654    bio->bi_rw |= REQ_THROTTLED;
655
656    throtl_trim_slice(td, tg, rw);
657}
658
659static int throtl_dispatch_tg(struct throtl_data *td, struct throtl_grp *tg,
660                struct bio_list *bl)
661{
662    unsigned int nr_reads = 0, nr_writes = 0;
663    unsigned int max_nr_reads = throtl_grp_quantum*3/4;
664    unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
665    struct bio *bio;
666
667    /* Try to dispatch 75% READS and 25% WRITES */
668
669    while ((bio = bio_list_peek(&tg->bio_lists[READ]))
670        && tg_may_dispatch(td, tg, bio, NULL)) {
671
672        tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
673        nr_reads++;
674
675        if (nr_reads >= max_nr_reads)
676            break;
677    }
678
679    while ((bio = bio_list_peek(&tg->bio_lists[WRITE]))
680        && tg_may_dispatch(td, tg, bio, NULL)) {
681
682        tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
683        nr_writes++;
684
685        if (nr_writes >= max_nr_writes)
686            break;
687    }
688
689    return nr_reads + nr_writes;
690}
691
692static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
693{
694    unsigned int nr_disp = 0;
695    struct throtl_grp *tg;
696    struct throtl_rb_root *st = &td->tg_service_tree;
697
698    while (1) {
699        tg = throtl_rb_first(st);
700
701        if (!tg)
702            break;
703
704        if (time_before(jiffies, tg->disptime))
705            break;
706
707        throtl_dequeue_tg(td, tg);
708
709        nr_disp += throtl_dispatch_tg(td, tg, bl);
710
711        if (tg->nr_queued[0] || tg->nr_queued[1]) {
712            tg_update_disptime(td, tg);
713            throtl_enqueue_tg(td, tg);
714        }
715
716        if (nr_disp >= throtl_quantum)
717            break;
718    }
719
720    return nr_disp;
721}
722
723static void throtl_process_limit_change(struct throtl_data *td)
724{
725    struct throtl_grp *tg;
726    struct hlist_node *pos, *n;
727
728    if (!atomic_read(&td->limits_changed))
729        return;
730
731    throtl_log(td, "limit changed =%d", atomic_read(&td->limits_changed));
732
733    /*
734     * Make sure updates from throtl_update_blkio_group_read_bps() group
735     * of functions to tg->limits_changed are visible. We do not
736     * want update td->limits_changed to be visible but update to
737     * tg->limits_changed not being visible yet on this cpu. Hence
738     * the read barrier.
739     */
740    smp_rmb();
741
742    hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
743        if (throtl_tg_on_rr(tg) && tg->limits_changed) {
744            throtl_log_tg(td, tg, "limit change rbps=%llu wbps=%llu"
745                " riops=%u wiops=%u", tg->bps[READ],
746                tg->bps[WRITE], tg->iops[READ],
747                tg->iops[WRITE]);
748            tg_update_disptime(td, tg);
749            tg->limits_changed = false;
750        }
751    }
752
753    smp_mb__before_atomic_dec();
754    atomic_dec(&td->limits_changed);
755    smp_mb__after_atomic_dec();
756}
757
758/* Dispatch throttled bios. Should be called without queue lock held. */
759static int throtl_dispatch(struct request_queue *q)
760{
761    struct throtl_data *td = q->td;
762    unsigned int nr_disp = 0;
763    struct bio_list bio_list_on_stack;
764    struct bio *bio;
765
766    spin_lock_irq(q->queue_lock);
767
768    throtl_process_limit_change(td);
769
770    if (!total_nr_queued(td))
771        goto out;
772
773    bio_list_init(&bio_list_on_stack);
774
775    throtl_log(td, "dispatch nr_queued=%lu read=%u write=%u",
776            total_nr_queued(td), td->nr_queued[READ],
777            td->nr_queued[WRITE]);
778
779    nr_disp = throtl_select_dispatch(td, &bio_list_on_stack);
780
781    if (nr_disp)
782        throtl_log(td, "bios disp=%u", nr_disp);
783
784    throtl_schedule_next_dispatch(td);
785out:
786    spin_unlock_irq(q->queue_lock);
787
788    /*
789     * If we dispatched some requests, unplug the queue to make sure
790     * immediate dispatch
791     */
792    if (nr_disp) {
793        while((bio = bio_list_pop(&bio_list_on_stack)))
794            generic_make_request(bio);
795        blk_unplug(q);
796    }
797    return nr_disp;
798}
799
800void blk_throtl_work(struct work_struct *work)
801{
802    struct throtl_data *td = container_of(work, struct throtl_data,
803                    throtl_work.work);
804    struct request_queue *q = td->queue;
805
806    throtl_dispatch(q);
807}
808
809/* Call with queue lock held */
810void throtl_schedule_delayed_work(struct request_queue *q, unsigned long delay)
811{
812
813    struct throtl_data *td = q->td;
814    struct delayed_work *dwork = &td->throtl_work;
815
816    if (total_nr_queued(td) > 0) {
817        /*
818         * We might have a work scheduled to be executed in future.
819         * Cancel that and schedule a new one.
820         */
821        __cancel_delayed_work(dwork);
822        kblockd_schedule_delayed_work(q, dwork, delay);
823        throtl_log(td, "schedule work. delay=%lu jiffies=%lu",
824                delay, jiffies);
825    }
826}
827EXPORT_SYMBOL(throtl_schedule_delayed_work);
828
829static void
830throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)
831{
832    /* Something wrong if we are trying to remove same group twice */
833    BUG_ON(hlist_unhashed(&tg->tg_node));
834
835    hlist_del_init(&tg->tg_node);
836
837    /*
838     * Put the reference taken at the time of creation so that when all
839     * queues are gone, group can be destroyed.
840     */
841    throtl_put_tg(tg);
842    td->nr_undestroyed_grps--;
843}
844
845static void throtl_release_tgs(struct throtl_data *td)
846{
847    struct hlist_node *pos, *n;
848    struct throtl_grp *tg;
849
850    hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
851        /*
852         * If cgroup removal path got to blk_group first and removed
853         * it from cgroup list, then it will take care of destroying
854         * cfqg also.
855         */
856        if (!blkiocg_del_blkio_group(&tg->blkg))
857            throtl_destroy_tg(td, tg);
858    }
859}
860
861static void throtl_td_free(struct throtl_data *td)
862{
863    kfree(td);
864}
865
866/*
867 * Blk cgroup controller notification saying that blkio_group object is being
868 * delinked as associated cgroup object is going away. That also means that
869 * no new IO will come in this group. So get rid of this group as soon as
870 * any pending IO in the group is finished.
871 *
872 * This function is called under rcu_read_lock(). key is the rcu protected
873 * pointer. That means "key" is a valid throtl_data pointer as long as we are
874 * rcu read lock.
875 *
876 * "key" was fetched from blkio_group under blkio_cgroup->lock. That means
877 * it should not be NULL as even if queue was going away, cgroup deltion
878 * path got to it first.
879 */
880void throtl_unlink_blkio_group(void *key, struct blkio_group *blkg)
881{
882    unsigned long flags;
883    struct throtl_data *td = key;
884
885    spin_lock_irqsave(td->queue->queue_lock, flags);
886    throtl_destroy_tg(td, tg_of_blkg(blkg));
887    spin_unlock_irqrestore(td->queue->queue_lock, flags);
888}
889
890/*
891 * For all update functions, key should be a valid pointer because these
892 * update functions are called under blkcg_lock, that means, blkg is
893 * valid and in turn key is valid. queue exit path can not race becuase
894 * of blkcg_lock
895 *
896 * Can not take queue lock in update functions as queue lock under blkcg_lock
897 * is not allowed. Under other paths we take blkcg_lock under queue_lock.
898 */
899static void throtl_update_blkio_group_read_bps(void *key,
900                struct blkio_group *blkg, u64 read_bps)
901{
902    struct throtl_data *td = key;
903
904    tg_of_blkg(blkg)->bps[READ] = read_bps;
905    /* Make sure read_bps is updated before setting limits_changed */
906    smp_wmb();
907    tg_of_blkg(blkg)->limits_changed = true;
908
909    /* Make sure tg->limits_changed is updated before td->limits_changed */
910    smp_mb__before_atomic_inc();
911    atomic_inc(&td->limits_changed);
912    smp_mb__after_atomic_inc();
913
914    /* Schedule a work now to process the limit change */
915    throtl_schedule_delayed_work(td->queue, 0);
916}
917
918static void throtl_update_blkio_group_write_bps(void *key,
919                struct blkio_group *blkg, u64 write_bps)
920{
921    struct throtl_data *td = key;
922
923    tg_of_blkg(blkg)->bps[WRITE] = write_bps;
924    smp_wmb();
925    tg_of_blkg(blkg)->limits_changed = true;
926    smp_mb__before_atomic_inc();
927    atomic_inc(&td->limits_changed);
928    smp_mb__after_atomic_inc();
929    throtl_schedule_delayed_work(td->queue, 0);
930}
931
932static void throtl_update_blkio_group_read_iops(void *key,
933            struct blkio_group *blkg, unsigned int read_iops)
934{
935    struct throtl_data *td = key;
936
937    tg_of_blkg(blkg)->iops[READ] = read_iops;
938    smp_wmb();
939    tg_of_blkg(blkg)->limits_changed = true;
940    smp_mb__before_atomic_inc();
941    atomic_inc(&td->limits_changed);
942    smp_mb__after_atomic_inc();
943    throtl_schedule_delayed_work(td->queue, 0);
944}
945
946static void throtl_update_blkio_group_write_iops(void *key,
947            struct blkio_group *blkg, unsigned int write_iops)
948{
949    struct throtl_data *td = key;
950
951    tg_of_blkg(blkg)->iops[WRITE] = write_iops;
952    smp_wmb();
953    tg_of_blkg(blkg)->limits_changed = true;
954    smp_mb__before_atomic_inc();
955    atomic_inc(&td->limits_changed);
956    smp_mb__after_atomic_inc();
957    throtl_schedule_delayed_work(td->queue, 0);
958}
959
960void throtl_shutdown_timer_wq(struct request_queue *q)
961{
962    struct throtl_data *td = q->td;
963
964    cancel_delayed_work_sync(&td->throtl_work);
965}
966
967static struct blkio_policy_type blkio_policy_throtl = {
968    .ops = {
969        .blkio_unlink_group_fn = throtl_unlink_blkio_group,
970        .blkio_update_group_read_bps_fn =
971                    throtl_update_blkio_group_read_bps,
972        .blkio_update_group_write_bps_fn =
973                    throtl_update_blkio_group_write_bps,
974        .blkio_update_group_read_iops_fn =
975                    throtl_update_blkio_group_read_iops,
976        .blkio_update_group_write_iops_fn =
977                    throtl_update_blkio_group_write_iops,
978    },
979    .plid = BLKIO_POLICY_THROTL,
980};
981
982int blk_throtl_bio(struct request_queue *q, struct bio **biop)
983{
984    struct throtl_data *td = q->td;
985    struct throtl_grp *tg;
986    struct bio *bio = *biop;
987    bool rw = bio_data_dir(bio), update_disptime = true;
988
989    if (bio->bi_rw & REQ_THROTTLED) {
990        bio->bi_rw &= ~REQ_THROTTLED;
991        return 0;
992    }
993
994    spin_lock_irq(q->queue_lock);
995    tg = throtl_get_tg(td);
996
997    if (tg->nr_queued[rw]) {
998        /*
999         * There is already another bio queued in same dir. No
1000         * need to update dispatch time.
1001         * Still update the disptime if rate limits on this group
1002         * were changed.
1003         */
1004        if (!tg->limits_changed)
1005            update_disptime = false;
1006        else
1007            tg->limits_changed = false;
1008
1009        goto queue_bio;
1010    }
1011
1012    /* Bio is with-in rate limit of group */
1013    if (tg_may_dispatch(td, tg, bio, NULL)) {
1014        throtl_charge_bio(tg, bio);
1015        goto out;
1016    }
1017
1018queue_bio:
1019    throtl_log_tg(td, tg, "[%c] bio. bdisp=%u sz=%u bps=%llu"
1020            " iodisp=%u iops=%u queued=%d/%d",
1021            rw == READ ? 'R' : 'W',
1022            tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],
1023            tg->io_disp[rw], tg->iops[rw],
1024            tg->nr_queued[READ], tg->nr_queued[WRITE]);
1025
1026    throtl_add_bio_tg(q->td, tg, bio);
1027    *biop = NULL;
1028
1029    if (update_disptime) {
1030        tg_update_disptime(td, tg);
1031        throtl_schedule_next_dispatch(td);
1032    }
1033
1034out:
1035    spin_unlock_irq(q->queue_lock);
1036    return 0;
1037}
1038
1039int blk_throtl_init(struct request_queue *q)
1040{
1041    struct throtl_data *td;
1042    struct throtl_grp *tg;
1043
1044    td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
1045    if (!td)
1046        return -ENOMEM;
1047
1048    INIT_HLIST_HEAD(&td->tg_list);
1049    td->tg_service_tree = THROTL_RB_ROOT;
1050    atomic_set(&td->limits_changed, 0);
1051
1052    /* Init root group */
1053    tg = &td->root_tg;
1054    INIT_HLIST_NODE(&tg->tg_node);
1055    RB_CLEAR_NODE(&tg->rb_node);
1056    bio_list_init(&tg->bio_lists[0]);
1057    bio_list_init(&tg->bio_lists[1]);
1058
1059    /* Practically unlimited BW */
1060    tg->bps[0] = tg->bps[1] = -1;
1061    tg->iops[0] = tg->iops[1] = -1;
1062
1063    /*
1064     * Set root group reference to 2. One reference will be dropped when
1065     * all groups on tg_list are being deleted during queue exit. Other
1066     * reference will remain there as we don't want to delete this group
1067     * as it is statically allocated and gets destroyed when throtl_data
1068     * goes away.
1069     */
1070    atomic_set(&tg->ref, 2);
1071    hlist_add_head(&tg->tg_node, &td->tg_list);
1072    td->nr_undestroyed_grps++;
1073
1074    INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
1075
1076    rcu_read_lock();
1077    blkiocg_add_blkio_group(&blkio_root_cgroup, &tg->blkg, (void *)td,
1078                    0, BLKIO_POLICY_THROTL);
1079    rcu_read_unlock();
1080
1081    /* Attach throtl data to request queue */
1082    td->queue = q;
1083    q->td = td;
1084    return 0;
1085}
1086
1087void blk_throtl_exit(struct request_queue *q)
1088{
1089    struct throtl_data *td = q->td;
1090    bool wait = false;
1091
1092    BUG_ON(!td);
1093
1094    throtl_shutdown_timer_wq(q);
1095
1096    spin_lock_irq(q->queue_lock);
1097    throtl_release_tgs(td);
1098
1099    /* If there are other groups */
1100    if (td->nr_undestroyed_grps > 0)
1101        wait = true;
1102
1103    spin_unlock_irq(q->queue_lock);
1104
1105    /*
1106     * Wait for tg->blkg->key accessors to exit their grace periods.
1107     * Do this wait only if there are other undestroyed groups out
1108     * there (other than root group). This can happen if cgroup deletion
1109     * path claimed the responsibility of cleaning up a group before
1110     * queue cleanup code get to the group.
1111     *
1112     * Do not call synchronize_rcu() unconditionally as there are drivers
1113     * which create/delete request queue hundreds of times during scan/boot
1114     * and synchronize_rcu() can take significant time and slow down boot.
1115     */
1116    if (wait)
1117        synchronize_rcu();
1118
1119    /*
1120     * Just being safe to make sure after previous flush if some body did
1121     * update limits through cgroup and another work got queued, cancel
1122     * it.
1123     */
1124    throtl_shutdown_timer_wq(q);
1125    throtl_td_free(td);
1126}
1127
1128static int __init throtl_init(void)
1129{
1130    blkio_policy_register(&blkio_policy_throtl);
1131    return 0;
1132}
1133
1134module_init(throtl_init);
1135

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