blob: 7f9b41f7ad8a2333ec40310825e5cf0764709d52 [file] [log] [blame]
/*
* Fast and scalable bitmap tagging variant. Uses sparser bitmaps spread
* over multiple cachelines to avoid ping-pong between multiple submitters
* or submitter and completer. Uses rolling wakeups to avoid falling of
* the scaling cliff when we run out of tags and have to start putting
* submitters to sleep.
*
* Uses active queue tracking to support fairer distribution of tags
* between multiple submitters when a shared tag map is used.
*
* Copyright (C) 2013-2014 Jens Axboe
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/blk-mq.h>
#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-tag.h"
static bool bt_has_free_tags(struct blk_mq_bitmap_tags *bt)
{
int i;
for (i = 0; i < bt->map_nr; i++) {
struct blk_align_bitmap *bm = &bt->map[i];
int ret;
ret = find_first_zero_bit(&bm->word, bm->depth);
if (ret < bm->depth)
return true;
}
return false;
}
bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
{
if (!tags)
return true;
return bt_has_free_tags(&tags->bitmap_tags);
}
static inline int bt_index_inc(int index)
{
return (index + 1) & (BT_WAIT_QUEUES - 1);
}
static inline void bt_index_atomic_inc(atomic_t *index)
{
int old = atomic_read(index);
int new = bt_index_inc(old);
atomic_cmpxchg(index, old, new);
}
/*
* If a previously inactive queue goes active, bump the active user count.
*/
bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
{
if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
!test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
atomic_inc(&hctx->tags->active_queues);
return true;
}
/*
* Wakeup all potentially sleeping on normal (non-reserved) tags
*/
static void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags)
{
struct blk_mq_bitmap_tags *bt;
int i, wake_index;
bt = &tags->bitmap_tags;
wake_index = atomic_read(&bt->wake_index);
for (i = 0; i < BT_WAIT_QUEUES; i++) {
struct bt_wait_state *bs = &bt->bs[wake_index];
if (waitqueue_active(&bs->wait))
wake_up(&bs->wait);
wake_index = bt_index_inc(wake_index);
}
}
/*
* If a previously busy queue goes inactive, potential waiters could now
* be allowed to queue. Wake them up and check.
*/
void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
{
struct blk_mq_tags *tags = hctx->tags;
if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
return;
atomic_dec(&tags->active_queues);
blk_mq_tag_wakeup_all(tags);
}
/*
* For shared tag users, we track the number of currently active users
* and attempt to provide a fair share of the tag depth for each of them.
*/
static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
struct blk_mq_bitmap_tags *bt)
{
unsigned int depth, users;
if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
return true;
if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
return true;
/*
* Don't try dividing an ant
*/
if (bt->depth == 1)
return true;
users = atomic_read(&hctx->tags->active_queues);
if (!users)
return true;
/*
* Allow at least some tags
*/
depth = max((bt->depth + users - 1) / users, 4U);
return atomic_read(&hctx->nr_active) < depth;
}
static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
{
int tag, org_last_tag, end;
bool wrap = last_tag != 0;
org_last_tag = last_tag;
end = bm->depth;
do {
restart:
tag = find_next_zero_bit(&bm->word, end, last_tag);
if (unlikely(tag >= end)) {
/*
* We started with an offset, start from 0 to
* exhaust the map.
*/
if (wrap) {
wrap = false;
end = org_last_tag;
last_tag = 0;
goto restart;
}
return -1;
}
last_tag = tag + 1;
} while (test_and_set_bit(tag, &bm->word));
return tag;
}
/*
* Straight forward bitmap tag implementation, where each bit is a tag
* (cleared == free, and set == busy). The small twist is using per-cpu
* last_tag caches, which blk-mq stores in the blk_mq_ctx software queue
* contexts. This enables us to drastically limit the space searched,
* without dirtying an extra shared cacheline like we would if we stored
* the cache value inside the shared blk_mq_bitmap_tags structure. On top
* of that, each word of tags is in a separate cacheline. This means that
* multiple users will tend to stick to different cachelines, at least
* until the map is exhausted.
*/
static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
unsigned int *tag_cache)
{
unsigned int last_tag, org_last_tag;
int index, i, tag;
if (!hctx_may_queue(hctx, bt))
return -1;
last_tag = org_last_tag = *tag_cache;
index = TAG_TO_INDEX(bt, last_tag);
for (i = 0; i < bt->map_nr; i++) {
tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag));
if (tag != -1) {
tag += (index << bt->bits_per_word);
goto done;
}
last_tag = 0;
if (++index >= bt->map_nr)
index = 0;
}
*tag_cache = 0;
return -1;
/*
* Only update the cache from the allocation path, if we ended
* up using the specific cached tag.
*/
done:
if (tag == org_last_tag) {
last_tag = tag + 1;
if (last_tag >= bt->depth - 1)
last_tag = 0;
*tag_cache = last_tag;
}
return tag;
}
static struct bt_wait_state *bt_wait_ptr(struct blk_mq_bitmap_tags *bt,
struct blk_mq_hw_ctx *hctx)
{
struct bt_wait_state *bs;
int wait_index;
if (!hctx)
return &bt->bs[0];
wait_index = atomic_read(&hctx->wait_index);
bs = &bt->bs[wait_index];
bt_index_atomic_inc(&hctx->wait_index);
return bs;
}
static int bt_get(struct blk_mq_alloc_data *data,
struct blk_mq_bitmap_tags *bt,
struct blk_mq_hw_ctx *hctx,
unsigned int *last_tag)
{
struct bt_wait_state *bs;
DEFINE_WAIT(wait);
int tag;
tag = __bt_get(hctx, bt, last_tag);
if (tag != -1)
return tag;
if (!(data->gfp & __GFP_WAIT))
return -1;
bs = bt_wait_ptr(bt, hctx);
do {
prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
tag = __bt_get(hctx, bt, last_tag);
if (tag != -1)
break;
blk_mq_put_ctx(data->ctx);
io_schedule();
data->ctx = blk_mq_get_ctx(data->q);
data->hctx = data->q->mq_ops->map_queue(data->q,
data->ctx->cpu);
if (data->reserved) {
bt = &data->hctx->tags->breserved_tags;
} else {
last_tag = &data->ctx->last_tag;
hctx = data->hctx;
bt = &hctx->tags->bitmap_tags;
}
finish_wait(&bs->wait, &wait);
bs = bt_wait_ptr(bt, hctx);
} while (1);
finish_wait(&bs->wait, &wait);
return tag;
}
static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
{
int tag;
tag = bt_get(data, &data->hctx->tags->bitmap_tags, data->hctx,
&data->ctx->last_tag);
if (tag >= 0)
return tag + data->hctx->tags->nr_reserved_tags;
return BLK_MQ_TAG_FAIL;
}
static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data *data)
{
int tag, zero = 0;
if (unlikely(!data->hctx->tags->nr_reserved_tags)) {
WARN_ON_ONCE(1);
return BLK_MQ_TAG_FAIL;
}
tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero);
if (tag < 0)
return BLK_MQ_TAG_FAIL;
return tag;
}
unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
{
if (!data->reserved)
return __blk_mq_get_tag(data);
return __blk_mq_get_reserved_tag(data);
}
static struct bt_wait_state *bt_wake_ptr(struct blk_mq_bitmap_tags *bt)
{
int i, wake_index;
wake_index = atomic_read(&bt->wake_index);
for (i = 0; i < BT_WAIT_QUEUES; i++) {
struct bt_wait_state *bs = &bt->bs[wake_index];
if (waitqueue_active(&bs->wait)) {
int o = atomic_read(&bt->wake_index);
if (wake_index != o)
atomic_cmpxchg(&bt->wake_index, o, wake_index);
return bs;
}
wake_index = bt_index_inc(wake_index);
}
return NULL;
}
static bool __bt_wake_up(struct blk_mq_bitmap_tags *bt)
{
struct bt_wait_state *bs;
unsigned int wake_batch;
int wait_cnt;
/* Ensure that the wait list checks occur after clear_bit(). */
smp_mb();
bs = bt_wake_ptr(bt);
if (!bs)
return false;
wait_cnt = atomic_dec_return(&bs->wait_cnt);
if (wait_cnt <= 0) {
int ret;
wake_batch = ACCESS_ONCE(bt->wake_cnt);
/*
* Pairs with the memory barrier in bt_update_count() to
* ensure that we see the batch size update before the wait
* count is reset.
*/
smp_mb__before_atomic();
/*
* For concurrent callers of this, the one that failed the
* atomic_cmpxhcg() race should call this function again
* to wakeup a new batch on a different 'bs'.
*/
ret = atomic_cmpxchg(&bs->wait_cnt, wait_cnt, wake_batch);
if (ret == wait_cnt) {
bt_index_atomic_inc(&bt->wake_index);
wake_up(&bs->wait);
return false;
}
return true;
}
return false;
}
static void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag)
{
const int index = TAG_TO_INDEX(bt, tag);
clear_bit(TAG_TO_BIT(bt, tag), &bt->map[index].word);
while (__bt_wake_up(bt))
;
}
static void __blk_mq_put_tag(struct blk_mq_tags *tags, unsigned int tag)
{
BUG_ON(tag >= tags->nr_tags);
bt_clear_tag(&tags->bitmap_tags, tag);
}
static void __blk_mq_put_reserved_tag(struct blk_mq_tags *tags,
unsigned int tag)
{
BUG_ON(tag >= tags->nr_reserved_tags);
bt_clear_tag(&tags->breserved_tags, tag);
}
void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
unsigned int *last_tag)
{
struct blk_mq_tags *tags = hctx->tags;
if (tag >= tags->nr_reserved_tags) {
const int real_tag = tag - tags->nr_reserved_tags;
__blk_mq_put_tag(tags, real_tag);
*last_tag = real_tag;
} else
__blk_mq_put_reserved_tag(tags, tag);
}
static void bt_for_each_free(struct blk_mq_bitmap_tags *bt,
unsigned long *free_map, unsigned int off)
{
int i;
for (i = 0; i < bt->map_nr; i++) {
struct blk_align_bitmap *bm = &bt->map[i];
int bit = 0;
do {
bit = find_next_zero_bit(&bm->word, bm->depth, bit);
if (bit >= bm->depth)
break;
__set_bit(bit + off, free_map);
bit++;
} while (1);
off += (1 << bt->bits_per_word);
}
}
void blk_mq_tag_busy_iter(struct blk_mq_tags *tags,
void (*fn)(void *, unsigned long *), void *data)
{
unsigned long *tag_map;
size_t map_size;
map_size = ALIGN(tags->nr_tags, BITS_PER_LONG) / BITS_PER_LONG;
tag_map = kzalloc(map_size * sizeof(unsigned long), GFP_ATOMIC);
if (!tag_map)
return;
bt_for_each_free(&tags->bitmap_tags, tag_map, tags->nr_reserved_tags);
if (tags->nr_reserved_tags)
bt_for_each_free(&tags->breserved_tags, tag_map, 0);
fn(data, tag_map);
kfree(tag_map);
}
EXPORT_SYMBOL(blk_mq_tag_busy_iter);
static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
{
unsigned int i, used;
for (i = 0, used = 0; i < bt->map_nr; i++) {
struct blk_align_bitmap *bm = &bt->map[i];
used += bitmap_weight(&bm->word, bm->depth);
}
return bt->depth - used;
}
static void bt_update_count(struct blk_mq_bitmap_tags *bt,
unsigned int depth)
{
unsigned int tags_per_word = 1U << bt->bits_per_word;
unsigned int map_depth = depth;
unsigned int wake_batch;
int i;
if (depth) {
for (i = 0; i < bt->map_nr; i++) {
bt->map[i].depth = min(map_depth, tags_per_word);
map_depth -= bt->map[i].depth;
}
}
wake_batch = BT_WAIT_BATCH;
if (wake_batch > depth / BT_WAIT_QUEUES)
wake_batch = max(1U, depth / BT_WAIT_QUEUES);
if (bt->wake_cnt != wake_batch) {
ACCESS_ONCE(bt->wake_cnt) = wake_batch;
/*
* Pairs with the memory barrier in bt_clear_tag() to ensure
* that the batch size is updated before the wait counts.
*/
smp_mb__before_atomic();
for (i = 0; i < BT_WAIT_QUEUES; i++)
atomic_set(&bt->bs[i].wait_cnt, 1);
}
bt->depth = depth;
}
static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
int node, bool reserved)
{
int i;
bt->bits_per_word = ilog2(BITS_PER_LONG);
/*
* Depth can be zero for reserved tags, that's not a failure
* condition.
*/
if (depth) {
unsigned int nr, tags_per_word;
tags_per_word = (1 << bt->bits_per_word);
/*
* If the tag space is small, shrink the number of tags
* per word so we spread over a few cachelines, at least.
* If less than 4 tags, just forget about it, it's not
* going to work optimally anyway.
*/
if (depth >= 4) {
while (tags_per_word * 4 > depth) {
bt->bits_per_word--;
tags_per_word = (1 << bt->bits_per_word);
}
}
nr = ALIGN(depth, tags_per_word) / tags_per_word;
bt->map = kzalloc_node(nr * sizeof(struct blk_align_bitmap),
GFP_KERNEL, node);
if (!bt->map)
return -ENOMEM;
bt->map_nr = nr;
}
bt->bs = kzalloc(BT_WAIT_QUEUES * sizeof(*bt->bs), GFP_KERNEL);
if (!bt->bs) {
kfree(bt->map);
bt->map = NULL;
return -ENOMEM;
}
bt_update_count(bt, depth);
for (i = 0; i < BT_WAIT_QUEUES; i++) {
init_waitqueue_head(&bt->bs[i].wait);
atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);
}
return 0;
}
static void bt_free(struct blk_mq_bitmap_tags *bt)
{
kfree(bt->map);
kfree(bt->bs);
}
static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
int node)
{
unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
if (bt_alloc(&tags->bitmap_tags, depth, node, false))
goto enomem;
if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, node, true))
goto enomem;
return tags;
enomem:
bt_free(&tags->bitmap_tags);
kfree(tags);
return NULL;
}
struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
unsigned int reserved_tags, int node)
{
struct blk_mq_tags *tags;
if (total_tags > BLK_MQ_TAG_MAX) {
pr_err("blk-mq: tag depth too large\n");
return NULL;
}
tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
if (!tags)
return NULL;
tags->nr_tags = total_tags;
tags->nr_reserved_tags = reserved_tags;
return blk_mq_init_bitmap_tags(tags, node);
}
void blk_mq_free_tags(struct blk_mq_tags *tags)
{
bt_free(&tags->bitmap_tags);
bt_free(&tags->breserved_tags);
kfree(tags);
}
void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *tag)
{
unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
*tag = prandom_u32() % depth;
}
int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
{
tdepth -= tags->nr_reserved_tags;
if (tdepth > tags->nr_tags)
return -EINVAL;
/*
* Don't need (or can't) update reserved tags here, they remain
* static and should never need resizing.
*/
bt_update_count(&tags->bitmap_tags, tdepth);
blk_mq_tag_wakeup_all(tags);
return 0;
}
ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
{
char *orig_page = page;
unsigned int free, res;
if (!tags)
return 0;
page += sprintf(page, "nr_tags=%u, reserved_tags=%u, "
"bits_per_word=%u\n",
tags->nr_tags, tags->nr_reserved_tags,
tags->bitmap_tags.bits_per_word);
free = bt_unused_tags(&tags->bitmap_tags);
res = bt_unused_tags(&tags->breserved_tags);
page += sprintf(page, "nr_free=%u, nr_reserved=%u\n", free, res);
page += sprintf(page, "active_queues=%u\n", atomic_read(&tags->active_queues));
return page - orig_page;
}