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/*
* Interface for controlling IO bandwidth on a request queue
*
* Copyright (C) 2010 Vivek Goyal <vgoyal@redhat.com>
*/

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/bio.h>
#include <linux/blktrace_api.h>
#include "blk-cgroup.h"
#include "blk.h"

/* Max dispatch from a group in 1 round */
static int throtl_grp_quantum = 8;

/* Total max dispatch from all groups in one round */
static int throtl_quantum = 32;

/* Throttling is performed over 100ms slice and after that slice is renewed */
static unsigned long throtl_slice = HZ/10; /* 100 ms */

static struct blkcg_policy blkcg_policy_throtl;

/* A workqueue to queue throttle related work */
static struct workqueue_struct *kthrotld_workqueue;
static void throtl_schedule_delayed_work(struct throtl_data *td,
unsigned long delay);

struct throtl_rb_root {
struct rb_root rb;
struct rb_node *left;
unsigned int count;
unsigned long min_disptime;
};

#define THROTL_RB_ROOT (struct throtl_rb_root) { .rb = RB_ROOT, .left = NULL, \
.count = 0, .min_disptime = 0}

#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)

/* Per-cpu group stats */
struct tg_stats_cpu {
/* total bytes transferred */
struct blkg_rwstat service_bytes;
/* total IOs serviced, post merge */
struct blkg_rwstat serviced;
};

struct throtl_grp {
/* must be the first member */
struct blkg_policy_data pd;

/* active throtl group service_tree member */
struct rb_node rb_node;

/*
* Dispatch time in jiffies. This is the estimated time when group
* will unthrottle and is ready to dispatch more bio. It is used as
* key to sort active groups in service tree.
*/
unsigned long disptime;

unsigned int flags;

/* Two lists for READ and WRITE */
struct bio_list bio_lists[2];

/* Number of queued bios on READ and WRITE lists */
unsigned int nr_queued[2];

/* bytes per second rate limits */
uint64_t bps[2];

/* IOPS limits */
unsigned int iops[2];

/* Number of bytes disptached in current slice */
uint64_t bytes_disp[2];
/* Number of bio's dispatched in current slice */
unsigned int io_disp[2];

/* When did we start a new slice */
unsigned long slice_start[2];
unsigned long slice_end[2];

/* Some throttle limits got updated for the group */
int limits_changed;

/* Per cpu stats pointer */
struct tg_stats_cpu __percpu *stats_cpu;

/* List of tgs waiting for per cpu stats memory to be allocated */
struct list_head stats_alloc_node;
};

struct throtl_data
{
/* service tree for active throtl groups */
struct throtl_rb_root tg_service_tree;

struct request_queue *queue;

/* Total Number of queued bios on READ and WRITE lists */
unsigned int nr_queued[2];

/*
* number of total undestroyed groups
*/
unsigned int nr_undestroyed_grps;

/* Work for dispatching throttled bios */
struct delayed_work throtl_work;

int limits_changed;
};

/* list and work item to allocate percpu group stats */
static DEFINE_SPINLOCK(tg_stats_alloc_lock);
static LIST_HEAD(tg_stats_alloc_list);

static void tg_stats_alloc_fn(struct work_struct *);
static DECLARE_DELAYED_WORK(tg_stats_alloc_work, tg_stats_alloc_fn);

static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
{
return pd ? container_of(pd, struct throtl_grp, pd) : NULL;
}

static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg)
{
return pd_to_tg(blkg_to_pd(blkg, &blkcg_policy_throtl));
}

static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
{
return pd_to_blkg(&tg->pd);
}

static inline struct throtl_grp *td_root_tg(struct throtl_data *td)
{
return blkg_to_tg(td->queue->root_blkg);
}

enum tg_state_flags {
THROTL_TG_FLAG_on_rr = 0, /* on round-robin busy list */
};

#define THROTL_TG_FNS(name) \
static inline void throtl_mark_tg_##name(struct throtl_grp *tg) \
{ \
(tg)->flags |= (1 << THROTL_TG_FLAG_##name); \
} \
static inline void throtl_clear_tg_##name(struct throtl_grp *tg) \
{ \
(tg)->flags &= ~(1 << THROTL_TG_FLAG_##name); \
} \
static inline int throtl_tg_##name(const struct throtl_grp *tg) \
{ \
return ((tg)->flags & (1 << THROTL_TG_FLAG_##name)) != 0; \
}

THROTL_TG_FNS(on_rr);

#define throtl_log_tg(td, tg, fmt, args...) do { \
char __pbuf[128]; \
\
blkg_path(tg_to_blkg(tg), __pbuf, sizeof(__pbuf)); \
blk_add_trace_msg((td)->queue, "throtl %s " fmt, __pbuf, ##args); \
} while (0)

#define throtl_log(td, fmt, args...) \
blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)

static inline unsigned int total_nr_queued(struct throtl_data *td)
{
return td->nr_queued[0] + td->nr_queued[1];
}

/*
* Worker for allocating per cpu stat for tgs. This is scheduled on the
* system_wq once there are some groups on the alloc_list waiting for
* allocation.
*/
static void tg_stats_alloc_fn(struct work_struct *work)
{
static struct tg_stats_cpu *stats_cpu; /* this fn is non-reentrant */
struct delayed_work *dwork = to_delayed_work(work);
bool empty = false;

alloc_stats:
if (!stats_cpu) {
stats_cpu = alloc_percpu(struct tg_stats_cpu);
if (!stats_cpu) {
/* allocation failed, try again after some time */
schedule_delayed_work(dwork, msecs_to_jiffies(10));
return;
}
}

spin_lock_irq(&tg_stats_alloc_lock);

if (!list_empty(&tg_stats_alloc_list)) {
struct throtl_grp *tg = list_first_entry(&tg_stats_alloc_list,
struct throtl_grp,
stats_alloc_node);
swap(tg->stats_cpu, stats_cpu);
list_del_init(&tg->stats_alloc_node);
}

empty = list_empty(&tg_stats_alloc_list);
spin_unlock_irq(&tg_stats_alloc_lock);
if (!empty)
goto alloc_stats;
}

static void throtl_pd_init(struct blkcg_gq *blkg)
{
struct throtl_grp *tg = blkg_to_tg(blkg);
unsigned long flags;

RB_CLEAR_NODE(&tg->rb_node);
bio_list_init(&tg->bio_lists[0]);
bio_list_init(&tg->bio_lists[1]);
tg->limits_changed = false;

tg->bps[READ] = -1;
tg->bps[WRITE] = -1;
tg->iops[READ] = -1;
tg->iops[WRITE] = -1;

/*
* Ugh... We need to perform per-cpu allocation for tg->stats_cpu
* but percpu allocator can't be called from IO path. Queue tg on
* tg_stats_alloc_list and allocate from work item.
*/
spin_lock_irqsave(&tg_stats_alloc_lock, flags);
list_add(&tg->stats_alloc_node, &tg_stats_alloc_list);
schedule_delayed_work(&tg_stats_alloc_work, 0);
spin_unlock_irqrestore(&tg_stats_alloc_lock, flags);
}

static void throtl_pd_exit(struct blkcg_gq *blkg)
{
struct throtl_grp *tg = blkg_to_tg(blkg);
unsigned long flags;

spin_lock_irqsave(&tg_stats_alloc_lock, flags);
list_del_init(&tg->stats_alloc_node);
spin_unlock_irqrestore(&tg_stats_alloc_lock, flags);

free_percpu(tg->stats_cpu);
}

static void throtl_pd_reset_stats(struct blkcg_gq *blkg)
{
struct throtl_grp *tg = blkg_to_tg(blkg);
int cpu;

if (tg->stats_cpu == NULL)
return;

for_each_possible_cpu(cpu) {
struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);

blkg_rwstat_reset(&sc->service_bytes);
blkg_rwstat_reset(&sc->serviced);
}
}

static struct throtl_grp *throtl_lookup_tg(struct throtl_data *td,
struct blkcg *blkcg)
{
/*
* This is the common case when there are no blkcgs. Avoid lookup
* in this case
*/
if (blkcg == &blkcg_root)
return td_root_tg(td);

return blkg_to_tg(blkg_lookup(blkcg, td->queue));
}

static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
struct blkcg *blkcg)
{
struct request_queue *q = td->queue;
struct throtl_grp *tg = NULL;

/*
* This is the common case when there are no blkcgs. Avoid lookup
* in this case
*/
if (blkcg == &blkcg_root) {
tg = td_root_tg(td);
} else {
struct blkcg_gq *blkg;

blkg = blkg_lookup_create(blkcg, q);

/* if %NULL and @q is alive, fall back to root_tg */
if (!IS_ERR(blkg))
tg = blkg_to_tg(blkg);
else if (!blk_queue_dead(q))
tg = td_root_tg(td);
}

return tg;
}

static struct throtl_grp *throtl_rb_first(struct throtl_rb_root *root)
{
/* Service tree is empty */
if (!root->count)
return NULL;

if (!root->left)
root->left = rb_first(&root->rb);

if (root->left)
return rb_entry_tg(root->left);

return NULL;
}

static void rb_erase_init(struct rb_node *n, struct rb_root *root)
{
rb_erase(n, root);
RB_CLEAR_NODE(n);
}

static void throtl_rb_erase(struct rb_node *n, struct throtl_rb_root *root)
{
if (root->left == n)
root->left = NULL;
rb_erase_init(n, &root->rb);
--root->count;
}

static void update_min_dispatch_time(struct throtl_rb_root *st)
{
struct throtl_grp *tg;

tg = throtl_rb_first(st);
if (!tg)
return;

st->min_disptime = tg->disptime;
}

static void
tg_service_tree_add(struct throtl_rb_root *st, struct throtl_grp *tg)
{
struct rb_node **node = &st->rb.rb_node;
struct rb_node *parent = NULL;
struct throtl_grp *__tg;
unsigned long key = tg->disptime;
int left = 1;

while (*node != NULL) {
parent = *node;
__tg = rb_entry_tg(parent);

if (time_before(key, __tg->disptime))
node = &parent->rb_left;
else {
node = &parent->rb_right;
left = 0;
}
}

if (left)
st->left = &tg->rb_node;

rb_link_node(&tg->rb_node, parent, node);
rb_insert_color(&tg->rb_node, &st->rb);
}

static void __throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
struct throtl_rb_root *st = &td->tg_service_tree;

tg_service_tree_add(st, tg);
throtl_mark_tg_on_rr(tg);
st->count++;
}

static void throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
if (!throtl_tg_on_rr(tg))
__throtl_enqueue_tg(td, tg);
}

static void __throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
throtl_rb_erase(&tg->rb_node, &td->tg_service_tree);
throtl_clear_tg_on_rr(tg);
}

static void throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
{
if (throtl_tg_on_rr(tg))
__throtl_dequeue_tg(td, tg);
}

static void throtl_schedule_next_dispatch(struct throtl_data *td)
{
struct throtl_rb_root *st = &td->tg_service_tree;

/*
* If there are more bios pending, schedule more work.
*/
if (!total_nr_queued(td))
return;

BUG_ON(!st->count);

update_min_dispatch_time(st);

if (time_before_eq(st->min_disptime, jiffies))
throtl_schedule_delayed_work(td, 0);
else
throtl_schedule_delayed_work(td, (st->min_disptime - jiffies));
}

static inline void
throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
{
tg->bytes_disp[rw] = 0;
tg->io_disp[rw] = 0;
tg->slice_start[rw] = jiffies;
tg->slice_end[rw] = jiffies + throtl_slice;
throtl_log_tg(td, tg, "[%c] new slice start=%lu end=%lu jiffies=%lu",
rw == READ ? 'R' : 'W', tg->slice_start[rw],
tg->slice_end[rw], jiffies);
}

static inline void throtl_set_slice_end(struct throtl_data *td,
struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
{
tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
}

static inline void throtl_extend_slice(struct throtl_data *td,
struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
{
tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
throtl_log_tg(td, tg, "[%c] extend slice start=%lu end=%lu jiffies=%lu",
rw == READ ? 'R' : 'W', tg->slice_start[rw],
tg->slice_end[rw], jiffies);
}

/* Determine if previously allocated or extended slice is complete or not */
static bool
throtl_slice_used(struct throtl_data *td, struct throtl_grp *tg, bool rw)
{
if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
return 0;

return 1;
}

/* Trim the used slices and adjust slice start accordingly */
static inline void
throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
{
unsigned long nr_slices, time_elapsed, io_trim;
u64 bytes_trim, tmp;

BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));

/*
* If bps are unlimited (-1), then time slice don't get
* renewed. Don't try to trim the slice if slice is used. A new
* slice will start when appropriate.
*/
if (throtl_slice_used(td, tg, rw))
return;

/*
* A bio has been dispatched. Also adjust slice_end. It might happen
* that initially cgroup limit was very low resulting in high
* slice_end, but later limit was bumped up and bio was dispached
* sooner, then we need to reduce slice_end. A high bogus slice_end
* is bad because it does not allow new slice to start.
*/

throtl_set_slice_end(td, tg, rw, jiffies + throtl_slice);

time_elapsed = jiffies - tg->slice_start[rw];

nr_slices = time_elapsed / throtl_slice;

if (!nr_slices)
return;
tmp = tg->bps[rw] * throtl_slice * nr_slices;
do_div(tmp, HZ);
bytes_trim = tmp;

io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;

if (!bytes_trim && !io_trim)
return;

if (tg->bytes_disp[rw] >= bytes_trim)
tg->bytes_disp[rw] -= bytes_trim;
else
tg->bytes_disp[rw] = 0;

if (tg->io_disp[rw] >= io_trim)
tg->io_disp[rw] -= io_trim;
else
tg->io_disp[rw] = 0;

tg->slice_start[rw] += nr_slices * throtl_slice;

throtl_log_tg(td, tg, "[%c] trim slice nr=%lu bytes=%llu io=%lu"
" start=%lu end=%lu jiffies=%lu",
rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
tg->slice_start[rw], tg->slice_end[rw], jiffies);
}

static bool tg_with_in_iops_limit(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio, unsigned long *wait)
{
bool rw = bio_data_dir(bio);
unsigned int io_allowed;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
u64 tmp;

jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];

/* Slice has just started. Consider one slice interval */
if (!jiffy_elapsed)
jiffy_elapsed_rnd = throtl_slice;

jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);

/*
* jiffy_elapsed_rnd should not be a big value as minimum iops can be
* 1 then at max jiffy elapsed should be equivalent of 1 second as we
* will allow dispatch after 1 second and after that slice should
* have been trimmed.
*/

tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
do_div(tmp, HZ);

if (tmp > UINT_MAX)
io_allowed = UINT_MAX;
else
io_allowed = tmp;

if (tg->io_disp[rw] + 1 <= io_allowed) {
if (wait)
*wait = 0;
return 1;
}

/* Calc approx time to dispatch */
jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1;

if (jiffy_wait > jiffy_elapsed)
jiffy_wait = jiffy_wait - jiffy_elapsed;
else
jiffy_wait = 1;

if (wait)
*wait = jiffy_wait;
return 0;
}

static bool tg_with_in_bps_limit(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio, unsigned long *wait)
{
bool rw = bio_data_dir(bio);
u64 bytes_allowed, extra_bytes, tmp;
unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;

jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];

/* Slice has just started. Consider one slice interval */
if (!jiffy_elapsed)
jiffy_elapsed_rnd = throtl_slice;

jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);

tmp = tg->bps[rw] * jiffy_elapsed_rnd;
do_div(tmp, HZ);
bytes_allowed = tmp;

if (tg->bytes_disp[rw] + bio->bi_size <= bytes_allowed) {
if (wait)
*wait = 0;
return 1;
}

/* Calc approx time to dispatch */
extra_bytes = tg->bytes_disp[rw] + bio->bi_size - bytes_allowed;
jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);

if (!jiffy_wait)
jiffy_wait = 1;

/*
* This wait time is without taking into consideration the rounding
* up we did. Add that time also.
*/
jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
if (wait)
*wait = jiffy_wait;
return 0;
}

static bool tg_no_rule_group(struct throtl_grp *tg, bool rw) {
if (tg->bps[rw] == -1 && tg->iops[rw] == -1)
return 1;
return 0;
}

/*
* Returns whether one can dispatch a bio or not. Also returns approx number
* of jiffies to wait before this bio is with-in IO rate and can be dispatched
*/
static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio, unsigned long *wait)
{
bool rw = bio_data_dir(bio);
unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;

/*
* Currently whole state machine of group depends on first bio
* queued in the group bio list. So one should not be calling
* this function with a different bio if there are other bios
* queued.
*/
BUG_ON(tg->nr_queued[rw] && bio != bio_list_peek(&tg->bio_lists[rw]));

/* If tg->bps = -1, then BW is unlimited */
if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
if (wait)
*wait = 0;
return 1;
}

/*
* If previous slice expired, start a new one otherwise renew/extend
* existing slice to make sure it is at least throtl_slice interval
* long since now.
*/
if (throtl_slice_used(td, tg, rw))
throtl_start_new_slice(td, tg, rw);
else {
if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
throtl_extend_slice(td, tg, rw, jiffies + throtl_slice);
}

if (tg_with_in_bps_limit(td, tg, bio, &bps_wait)
&& tg_with_in_iops_limit(td, tg, bio, &iops_wait)) {
if (wait)
*wait = 0;
return 1;
}

max_wait = max(bps_wait, iops_wait);

if (wait)
*wait = max_wait;

if (time_before(tg->slice_end[rw], jiffies + max_wait))
throtl_extend_slice(td, tg, rw, jiffies + max_wait);

return 0;
}

static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes,
int rw)
{
struct throtl_grp *tg = blkg_to_tg(blkg);
struct tg_stats_cpu *stats_cpu;
unsigned long flags;

/* If per cpu stats are not allocated yet, don't do any accounting. */
if (tg->stats_cpu == NULL)
return;

/*
* Disabling interrupts to provide mutual exclusion between two
* writes on same cpu. It probably is not needed for 64bit. Not
* optimizing that case yet.
*/
local_irq_save(flags);

stats_cpu = this_cpu_ptr(tg->stats_cpu);

blkg_rwstat_add(&stats_cpu->serviced, rw, 1);
blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes);

local_irq_restore(flags);
}

static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
{
bool rw = bio_data_dir(bio);

/* Charge the bio to the group */
tg->bytes_disp[rw] += bio->bi_size;
tg->io_disp[rw]++;

throtl_update_dispatch_stats(tg_to_blkg(tg), bio->bi_size, bio->bi_rw);
}

static void throtl_add_bio_tg(struct throtl_data *td, struct throtl_grp *tg,
struct bio *bio)
{
bool rw = bio_data_dir(bio);

bio_list_add(&tg->bio_lists[rw], bio);
/* Take a bio reference on tg */
blkg_get(tg_to_blkg(tg));
tg->nr_queued[rw]++;
td->nr_queued[rw]++;
throtl_enqueue_tg(td, tg);
}

static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
{
unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
struct bio *bio;

if ((bio = bio_list_peek(&tg->bio_lists[READ])))
tg_may_dispatch(td, tg, bio, &read_wait);

if ((bio = bio_list_peek(&tg->bio_lists[WRITE])))
tg_may_dispatch(td, tg, bio, &write_wait);

min_wait = min(read_wait, write_wait);
disptime = jiffies + min_wait;

/* Update dispatch time */
throtl_dequeue_tg(td, tg);
tg->disptime = disptime;
throtl_enqueue_tg(td, tg);
}

static void tg_dispatch_one_bio(struct throtl_data *td, struct throtl_grp *tg,
bool rw, struct bio_list *bl)
{
struct bio *bio;

bio = bio_list_pop(&tg->bio_lists[rw]);
tg->nr_queued[rw]--;
/* Drop bio reference on blkg */
blkg_put(tg_to_blkg(tg));

BUG_ON(td->nr_queued[rw] <= 0);
td->nr_queued[rw]--;

throtl_charge_bio(tg, bio);
bio_list_add(bl, bio);
bio->bi_rw |= REQ_THROTTLED;

throtl_trim_slice(td, tg, rw);
}

static int throtl_dispatch_tg(struct throtl_data *td, struct throtl_grp *tg,
struct bio_list *bl)
{
unsigned int nr_reads = 0, nr_writes = 0;
unsigned int max_nr_reads = throtl_grp_quantum*3/4;
unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
struct bio *bio;

/* Try to dispatch 75% READS and 25% WRITES */

while ((bio = bio_list_peek(&tg->bio_lists[READ]))
&& tg_may_dispatch(td, tg, bio, NULL)) {

tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
nr_reads++;

if (nr_reads >= max_nr_reads)
break;
}

while ((bio = bio_list_peek(&tg->bio_lists[WRITE]))
&& tg_may_dispatch(td, tg, bio, NULL)) {

tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
nr_writes++;

if (nr_writes >= max_nr_writes)
break;
}

return nr_reads + nr_writes;
}

static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
{
unsigned int nr_disp = 0;
struct throtl_grp *tg;
struct throtl_rb_root *st = &td->tg_service_tree;

while (1) {
tg = throtl_rb_first(st);

if (!tg)
break;

if (time_before(jiffies, tg->disptime))
break;

throtl_dequeue_tg(td, tg);

nr_disp += throtl_dispatch_tg(td, tg, bl);

if (tg->nr_queued[0] || tg->nr_queued[1]) {
tg_update_disptime(td, tg);
throtl_enqueue_tg(td, tg);
}

if (nr_disp >= throtl_quantum)
break;
}

return nr_disp;
}

static void throtl_process_limit_change(struct throtl_data *td)
{
struct request_queue *q = td->queue;
struct blkcg_gq *blkg, *n;

if (!td->limits_changed)
return;

xchg(&td->limits_changed, false);

throtl_log(td, "limits changed");

list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
struct throtl_grp *tg = blkg_to_tg(blkg);

if (!tg->limits_changed)
continue;

if (!xchg(&tg->limits_changed, false))
continue;

throtl_log_tg(td, tg, "limit change rbps=%llu wbps=%llu"
" riops=%u wiops=%u", tg->bps[READ], tg->bps[WRITE],
tg->iops[READ], tg->iops[WRITE]);

/*
* Restart the slices for both READ and WRITES. It
* might happen that a group's limit are dropped
* suddenly and we don't want to account recently
* dispatched IO with new low rate
*/
throtl_start_new_slice(td, tg, 0);
throtl_start_new_slice(td, tg, 1);

if (throtl_tg_on_rr(tg))
tg_update_disptime(td, tg);
}
}

/* Dispatch throttled bios. Should be called without queue lock held. */
static int throtl_dispatch(struct request_queue *q)
{
struct throtl_data *td = q->td;
unsigned int nr_disp = 0;
struct bio_list bio_list_on_stack;
struct bio *bio;
struct blk_plug plug;

spin_lock_irq(q->queue_lock);

throtl_process_limit_change(td);

if (!total_nr_queued(td))
goto out;

bio_list_init(&bio_list_on_stack);

throtl_log(td, "dispatch nr_queued=%u read=%u write=%u",
total_nr_queued(td), td->nr_queued[READ],
td->nr_queued[WRITE]);

nr_disp = throtl_select_dispatch(td, &bio_list_on_stack);

if (nr_disp)
throtl_log(td, "bios disp=%u", nr_disp);

throtl_schedule_next_dispatch(td);
out:
spin_unlock_irq(q->queue_lock);

/*
* If we dispatched some requests, unplug the queue to make sure
* immediate dispatch
*/
if (nr_disp) {
blk_start_plug(&plug);
while((bio = bio_list_pop(&bio_list_on_stack)))
generic_make_request(bio);
blk_finish_plug(&plug);
}
return nr_disp;
}

void blk_throtl_work(struct work_struct *work)
{
struct throtl_data *td = container_of(work, struct throtl_data,
throtl_work.work);
struct request_queue *q = td->queue;

throtl_dispatch(q);
}

/* Call with queue lock held */
static void
throtl_schedule_delayed_work(struct throtl_data *td, unsigned long delay)
{

struct delayed_work *dwork = &td->throtl_work;

/* schedule work if limits changed even if no bio is queued */
if (total_nr_queued(td) || td->limits_changed) {
mod_delayed_work(kthrotld_workqueue, dwork, delay);
throtl_log(td, "schedule work. delay=%lu jiffies=%lu",
delay, jiffies);
}
}

static u64 tg_prfill_cpu_rwstat(struct seq_file *sf,
struct blkg_policy_data *pd, int off)
{
struct throtl_grp *tg = pd_to_tg(pd);
struct blkg_rwstat rwstat = { }, tmp;
int i, cpu;

for_each_possible_cpu(cpu) {
struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);

tmp = blkg_rwstat_read((void *)sc + off);
for (i = 0; i < BLKG_RWSTAT_NR; i++)
rwstat.cnt[i] += tmp.cnt[i];
}

return __blkg_prfill_rwstat(sf, pd, &rwstat);
}

static int tg_print_cpu_rwstat(struct cgroup *cgrp, struct cftype *cft,
struct seq_file *sf)
{
struct blkcg *blkcg = cgroup_to_blkcg(cgrp);

blkcg_print_blkgs(sf, blkcg, tg_prfill_cpu_rwstat, &blkcg_policy_throtl,
cft->private, true);
return 0;
}

static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
int off)
{
struct throtl_grp *tg = pd_to_tg(pd);
u64 v = *(u64 *)((void *)tg + off);

if (v == -1)
return 0;
return __blkg_prfill_u64(sf, pd, v);
}

static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
int off)
{
struct throtl_grp *tg = pd_to_tg(pd);
unsigned int v = *(unsigned int *)((void *)tg + off);

if (v == -1)
return 0;
return __blkg_prfill_u64(sf, pd, v);
}

static int tg_print_conf_u64(struct cgroup *cgrp, struct cftype *cft,
struct seq_file *sf)
{
blkcg_print_blkgs(sf, cgroup_to_blkcg(cgrp), tg_prfill_conf_u64,
&blkcg_policy_throtl, cft->private, false);
return 0;
}

static int tg_print_conf_uint(struct cgroup *cgrp, struct cftype *cft,
struct seq_file *sf)
{
blkcg_print_blkgs(sf, cgroup_to_blkcg(cgrp), tg_prfill_conf_uint,
&blkcg_policy_throtl, cft->private, false);
return 0;
}

static int tg_set_conf(struct cgroup *cgrp, struct cftype *cft, const char *buf,
bool is_u64)
{
struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
struct blkg_conf_ctx ctx;
struct throtl_grp *tg;
struct throtl_data *td;
int ret;

ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
if (ret)
return ret;

tg = blkg_to_tg(ctx.blkg);
td = ctx.blkg->q->td;

if (!ctx.v)
ctx.v = -1;

if (is_u64)
*(u64 *)((void *)tg + cft->private) = ctx.v;
else
*(unsigned int *)((void *)tg + cft->private) = ctx.v;

/* XXX: we don't need the following deferred processing */
xchg(&tg->limits_changed, true);
xchg(&td->limits_changed, true);
throtl_schedule_delayed_work(td, 0);

blkg_conf_finish(&ctx);
return 0;
}

static int tg_set_conf_u64(struct cgroup *cgrp, struct cftype *cft,
const char *buf)
{
return tg_set_conf(cgrp, cft, buf, true);
}

static int tg_set_conf_uint(struct cgroup *cgrp, struct cftype *cft,
const char *buf)
{
return tg_set_conf(cgrp, cft, buf, false);
}

static struct cftype throtl_files[] = {
{
.name = "throttle.read_bps_device",
.private = offsetof(struct throtl_grp, bps[READ]),
.read_seq_string = tg_print_conf_u64,
.write_string = tg_set_conf_u64,
.max_write_len = 256,
},
{
.name = "throttle.write_bps_device",
.private = offsetof(struct throtl_grp, bps[WRITE]),
.read_seq_string = tg_print_conf_u64,
.write_string = tg_set_conf_u64,
.max_write_len = 256,
},
{
.name = "throttle.read_iops_device",
.private = offsetof(struct throtl_grp, iops[READ]),
.read_seq_string = tg_print_conf_uint,
.write_string = tg_set_conf_uint,
.max_write_len = 256,
},
{
.name = "throttle.write_iops_device",
.private = offsetof(struct throtl_grp, iops[WRITE]),
.read_seq_string = tg_print_conf_uint,
.write_string = tg_set_conf_uint,
.max_write_len = 256,
},
{
.name = "throttle.io_service_bytes",
.private = offsetof(struct tg_stats_cpu, service_bytes),
.read_seq_string = tg_print_cpu_rwstat,
},
{
.name = "throttle.io_serviced",
.private = offsetof(struct tg_stats_cpu, serviced),
.read_seq_string = tg_print_cpu_rwstat,
},
{ } /* terminate */
};

static void throtl_shutdown_wq(struct request_queue *q)
{
struct throtl_data *td = q->td;

cancel_delayed_work_sync(&td->throtl_work);
}

static struct blkcg_policy blkcg_policy_throtl = {
.pd_size = sizeof(struct throtl_grp),
.cftypes = throtl_files,

.pd_init_fn = throtl_pd_init,
.pd_exit_fn = throtl_pd_exit,
.pd_reset_stats_fn = throtl_pd_reset_stats,
};

bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
{
struct throtl_data *td = q->td;
struct throtl_grp *tg;
bool rw = bio_data_dir(bio), update_disptime = true;
struct blkcg *blkcg;
bool throttled = false;

if (bio->bi_rw & REQ_THROTTLED) {
bio->bi_rw &= ~REQ_THROTTLED;
goto out;
}

/*
* A throtl_grp pointer retrieved under rcu can be used to access
* basic fields like stats and io rates. If a group has no rules,
* just update the dispatch stats in lockless manner and return.
*/
rcu_read_lock();
blkcg = bio_blkcg(bio);
tg = throtl_lookup_tg(td, blkcg);
if (tg) {
if (tg_no_rule_group(tg, rw)) {
throtl_update_dispatch_stats(tg_to_blkg(tg),
bio->bi_size, bio->bi_rw);
goto out_unlock_rcu;
}
}

/*
* Either group has not been allocated yet or it is not an unlimited
* IO group
*/
spin_lock_irq(q->queue_lock);
tg = throtl_lookup_create_tg(td, blkcg);
if (unlikely(!tg))
goto out_unlock;

if (tg->nr_queued[rw]) {
/*
* There is already another bio queued in same dir. No
* need to update dispatch time.
*/
update_disptime = false;
goto queue_bio;

}

/* Bio is with-in rate limit of group */
if (tg_may_dispatch(td, tg, bio, NULL)) {
throtl_charge_bio(tg, bio);

/*
* We need to trim slice even when bios are not being queued
* otherwise it might happen that a bio is not queued for
* a long time and slice keeps on extending and trim is not
* called for a long time. Now if limits are reduced suddenly
* we take into account all the IO dispatched so far at new
* low rate and * newly queued IO gets a really long dispatch
* time.
*
* So keep on trimming slice even if bio is not queued.
*/
throtl_trim_slice(td, tg, rw);
goto out_unlock;
}

queue_bio:
throtl_log_tg(td, tg, "[%c] bio. bdisp=%llu sz=%u bps=%llu"
" iodisp=%u iops=%u queued=%d/%d",
rw == READ ? 'R' : 'W',
tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],
tg->io_disp[rw], tg->iops[rw],
tg->nr_queued[READ], tg->nr_queued[WRITE]);

bio_associate_current(bio);
throtl_add_bio_tg(q->td, tg, bio);
throttled = true;

if (update_disptime) {
tg_update_disptime(td, tg);
throtl_schedule_next_dispatch(td);
}

out_unlock:
spin_unlock_irq(q->queue_lock);
out_unlock_rcu:
rcu_read_unlock();
out:
return throttled;
}

/**
* blk_throtl_drain - drain throttled bios
* @q: request_queue to drain throttled bios for
*
* Dispatch all currently throttled bios on @q through ->make_request_fn().
*/
void blk_throtl_drain(struct request_queue *q)
__releases(q->queue_lock) __acquires(q->queue_lock)
{
struct throtl_data *td = q->td;
struct throtl_rb_root *st = &td->tg_service_tree;
struct throtl_grp *tg;
struct bio_list bl;
struct bio *bio;

queue_lockdep_assert_held(q);

bio_list_init(&bl);

while ((tg = throtl_rb_first(st))) {
throtl_dequeue_tg(td, tg);

while ((bio = bio_list_peek(&tg->bio_lists[READ])))
tg_dispatch_one_bio(td, tg, bio_data_dir(bio), &bl);
while ((bio = bio_list_peek(&tg->bio_lists[WRITE])))
tg_dispatch_one_bio(td, tg, bio_data_dir(bio), &bl);
}
spin_unlock_irq(q->queue_lock);

while ((bio = bio_list_pop(&bl)))
generic_make_request(bio);

spin_lock_irq(q->queue_lock);
}

int blk_throtl_init(struct request_queue *q)
{
struct throtl_data *td;
int ret;

td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
if (!td)
return -ENOMEM;

td->tg_service_tree = THROTL_RB_ROOT;
td->limits_changed = false;
INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);

q->td = td;
td->queue = q;

/* activate policy */
ret = blkcg_activate_policy(q, &blkcg_policy_throtl);
if (ret)
kfree(td);
return ret;
}

void blk_throtl_exit(struct request_queue *q)
{
BUG_ON(!q->td);
throtl_shutdown_wq(q);
blkcg_deactivate_policy(q, &blkcg_policy_throtl);
kfree(q->td);
}

static int __init throtl_init(void)
{
kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
if (!kthrotld_workqueue)
panic("Failed to create kthrotld\n");

return blkcg_policy_register(&blkcg_policy_throtl);
}

module_init(throtl_init);
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