Merge branch 'for-3.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu

[mirror_ubuntu-artful-kernel.git] / block / blk-mq-tag.c

/*
 * 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 tags
 */
void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
{
        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 (include_reserve) {
                bt = &tags->breserved_tags;
                if (waitqueue_active(&bt->bs[0].wait))
                        wake_up(&bt->bs[0].wait);
        }
}

/*
 * 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, false);
}

/*
 * 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;

                /*
                 * We're out of tags on this hardware queue, kick any
                 * pending IO submits before going to sleep waiting for
                 * some to complete.
                 */
                blk_mq_run_hw_queue(hctx, false);

                /*
                 * Retry tag allocation after running the hardware queue,
                 * as running the queue may also have found completions.
                 */
                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 void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag)
{
        const int index = TAG_TO_INDEX(bt, tag);
        struct bt_wait_state *bs;
        int wait_cnt;

        clear_bit(TAG_TO_BIT(bt, tag), &bt->map[index].word);

        /* Ensure that the wait list checks occur after clear_bit(). */
        smp_mb();

        bs = bt_wake_ptr(bt);
        if (!bs)
                return;

        wait_cnt = atomic_dec_return(&bs->wait_cnt);
        if (unlikely(wait_cnt < 0))
                wait_cnt = atomic_inc_return(&bs->wait_cnt);
        if (wait_cnt == 0) {
                atomic_add(bt->wake_cnt, &bs->wait_cnt);
                bt_index_atomic_inc(&bt->wake_index);
                wake_up(&bs->wait);
        }
}

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;

                BUG_ON(real_tag >= tags->nr_tags);
                bt_clear_tag(&tags->bitmap_tags, real_tag);
                *last_tag = real_tag;
        } else {
                BUG_ON(tag >= tags->nr_reserved_tags);
                bt_clear_tag(&tags->breserved_tags, tag);
        }
}

static void bt_for_each(struct blk_mq_hw_ctx *hctx,
                struct blk_mq_bitmap_tags *bt, unsigned int off,
                busy_iter_fn *fn, void *data, bool reserved)
{
        struct request *rq;
        int bit, i;

        for (i = 0; i < bt->map_nr; i++) {
                struct blk_align_bitmap *bm = &bt->map[i];

                for (bit = find_first_bit(&bm->word, bm->depth);
                     bit < bm->depth;
                     bit = find_next_bit(&bm->word, bm->depth, bit + 1)) {
                        rq = blk_mq_tag_to_rq(hctx->tags, off + bit);
                        if (rq->q == hctx->queue)
                                fn(hctx, rq, data, reserved);
                }

                off += (1 << bt->bits_per_word);
        }
}

void blk_mq_tag_busy_iter(struct blk_mq_hw_ctx *hctx, busy_iter_fn *fn,
                void *priv)
{
        struct blk_mq_tags *tags = hctx->tags;

        if (tags->nr_reserved_tags)
                bt_for_each(hctx, &tags->breserved_tags, 0, fn, priv, true);
        bt_for_each(hctx, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv,
                        false);
}
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;

        if (depth) {
                int i;

                for (i = 0; i < bt->map_nr; i++) {
                        bt->map[i].depth = min(map_depth, tags_per_word);
                        map_depth -= bt->map[i].depth;
                }
        }

        bt->wake_cnt = BT_WAIT_BATCH;
        if (bt->wake_cnt > depth / BT_WAIT_QUEUES)
                bt->wake_cnt = max(1U, depth / BT_WAIT_QUEUES);

        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);
                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, false);
        return 0;
}

/**
 * blk_mq_unique_tag() - return a tag that is unique queue-wide
 * @rq: request for which to compute a unique tag
 *
 * The tag field in struct request is unique per hardware queue but not over
 * all hardware queues. Hence this function that returns a tag with the
 * hardware context index in the upper bits and the per hardware queue tag in
 * the lower bits.
 *
 * Note: When called for a request that is queued on a non-multiqueue request
 * queue, the hardware context index is set to zero.
 */
u32 blk_mq_unique_tag(struct request *rq)
{
        struct request_queue *q = rq->q;
        struct blk_mq_hw_ctx *hctx;
        int hwq = 0;

        if (q->mq_ops) {
                hctx = q->mq_ops->map_queue(q, rq->mq_ctx->cpu);
                hwq = hctx->queue_num;
        }

        return (hwq << BLK_MQ_UNIQUE_TAG_BITS) |
                (rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
}
EXPORT_SYMBOL(blk_mq_unique_tag);

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;
}