+/*
+ * 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/percpu_ida.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 void bt_index_inc(unsigned int *index)
+{
+ *index = (*index + 1) & (BT_WAIT_QUEUES - 1);
+}
+
/*
- * Per tagged queue (tag address space) map
+ * If a previously inactive queue goes active, bump the active user count.
*/
-struct blk_mq_tags {
- unsigned int nr_tags;
- unsigned int nr_reserved_tags;
- unsigned int nr_batch_move;
- unsigned int nr_max_cache;
+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);
- struct percpu_ida free_tags;
- struct percpu_ida reserved_tags;
-};
+ return true;
+}
-void blk_mq_wait_for_tags(struct blk_mq_tags *tags)
+/*
+ * Wakeup all potentially sleeping on normal (non-reserved) tags
+ */
+static void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags)
{
- int tag = blk_mq_get_tag(tags, __GFP_WAIT, false);
- blk_mq_put_tag(tags, tag);
+ struct blk_mq_bitmap_tags *bt;
+ int i, wake_index;
+
+ bt = &tags->bitmap_tags;
+ wake_index = 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);
+
+ bt_index_inc(&wake_index);
+ }
}
-bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
+/*
+ * 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)
{
- return !tags ||
- percpu_ida_free_tags(&tags->free_tags, nr_cpu_ids) != 0;
+ int tag, org_last_tag, end;
+
+ 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 (org_last_tag && last_tag) {
+ end = last_tag;
+ last_tag = 0;
+ goto restart;
+ }
+ return -1;
+ }
+ last_tag = tag + 1;
+ } while (test_and_set_bit_lock(tag, &bm->word));
+
+ return tag;
}
-static unsigned int __blk_mq_get_tag(struct blk_mq_tags *tags, gfp_t gfp)
+/*
+ * 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;
+
+ if (!hctx)
+ return &bt->bs[0];
+
+ bs = &bt->bs[hctx->wait_index];
+ bt_index_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 = percpu_ida_alloc(&tags->free_tags, (gfp & __GFP_WAIT) ?
- TASK_UNINTERRUPTIBLE : TASK_RUNNING);
- if (tag < 0)
- return BLK_MQ_TAG_FAIL;
- return tag + tags->nr_reserved_tags;
+ 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 {
+ bool was_empty;
+
+ was_empty = list_empty(&wait.task_list);
+ prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
+
+ tag = __bt_get(hctx, bt, last_tag);
+ if (tag != -1)
+ break;
+
+ if (was_empty)
+ atomic_set(&bs->wait_cnt, bt->wake_cnt);
+
+ 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_reserved_tag(struct blk_mq_tags *tags,
- gfp_t gfp)
+static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
{
int tag;
- if (unlikely(!tags->nr_reserved_tags)) {
+ 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 = percpu_ida_alloc(&tags->reserved_tags, (gfp & __GFP_WAIT) ?
- TASK_UNINTERRUPTIBLE : TASK_RUNNING);
+ 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_tags *tags, gfp_t gfp, bool reserved)
+unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
{
- if (!reserved)
- return __blk_mq_get_tag(tags, gfp);
+ if (!data->reserved)
+ return __blk_mq_get_tag(data);
- return __blk_mq_get_reserved_tag(tags, gfp);
+ 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 = 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)) {
+ if (wake_index != bt->wake_index)
+ bt->wake_index = wake_index;
+
+ return bs;
+ }
+
+ 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;
+
+ /*
+ * The unlock memory barrier need to order access to req in free
+ * path and clearing tag bit
+ */
+ clear_bit_unlock(TAG_TO_BIT(bt, tag), &bt->map[index].word);
+
+ bs = bt_wake_ptr(bt);
+ if (bs && atomic_dec_and_test(&bs->wait_cnt)) {
+ atomic_set(&bs->wait_cnt, bt->wake_cnt);
+ bt_index_inc(&bt->wake_index);
+ wake_up(&bs->wait);
+ }
}
static void __blk_mq_put_tag(struct blk_mq_tags *tags, unsigned int tag)
{
BUG_ON(tag >= tags->nr_tags);
- percpu_ida_free(&tags->free_tags, tag - tags->nr_reserved_tags);
+ bt_clear_tag(&tags->bitmap_tags, tag);
}
static void __blk_mq_put_reserved_tag(struct blk_mq_tags *tags,
{
BUG_ON(tag >= tags->nr_reserved_tags);
- percpu_ida_free(&tags->reserved_tags, tag);
+ bt_clear_tag(&tags->breserved_tags, tag);
}
-void blk_mq_put_tag(struct blk_mq_tags *tags, unsigned int tag)
+void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
+ unsigned int *last_tag)
{
- if (tag >= tags->nr_reserved_tags)
- __blk_mq_put_tag(tags, tag);
- else
+ 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 int __blk_mq_tag_iter(unsigned id, void *data)
+static void bt_for_each_free(struct blk_mq_bitmap_tags *bt,
+ unsigned long *free_map, unsigned int off)
{
- unsigned long *tag_map = data;
- __set_bit(id, tag_map);
- return 0;
+ 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,
if (!tag_map)
return;
- percpu_ida_for_each_free(&tags->free_tags, __blk_mq_tag_iter, tag_map);
+ bt_for_each_free(&tags->bitmap_tags, tag_map, tags->nr_reserved_tags);
if (tags->nr_reserved_tags)
- percpu_ida_for_each_free(&tags->reserved_tags, __blk_mq_tag_iter,
- tag_map);
+ 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;
+
+ 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 / 4)
+ bt->wake_cnt = max(1U, depth / 4);
+
+ 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;
+ }
+
+ for (i = 0; i < BT_WAIT_QUEUES; i++)
+ init_waitqueue_head(&bt->bs[i].wait);
+
+ bt_update_count(bt, depth);
+ 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)
{
- unsigned int nr_tags, nr_cache;
struct blk_mq_tags *tags;
- int ret;
if (total_tags > BLK_MQ_TAG_MAX) {
pr_err("blk-mq: tag depth too large\n");
if (!tags)
return NULL;
- nr_tags = total_tags - reserved_tags;
- nr_cache = nr_tags / num_possible_cpus();
-
- if (nr_cache < BLK_MQ_TAG_CACHE_MIN)
- nr_cache = BLK_MQ_TAG_CACHE_MIN;
- else if (nr_cache > BLK_MQ_TAG_CACHE_MAX)
- nr_cache = BLK_MQ_TAG_CACHE_MAX;
-
tags->nr_tags = total_tags;
tags->nr_reserved_tags = reserved_tags;
- tags->nr_max_cache = nr_cache;
- tags->nr_batch_move = max(1u, nr_cache / 2);
- ret = __percpu_ida_init(&tags->free_tags, tags->nr_tags -
- tags->nr_reserved_tags,
- tags->nr_max_cache,
- tags->nr_batch_move);
- if (ret)
- goto err_free_tags;
+ return blk_mq_init_bitmap_tags(tags, node);
+}
- if (reserved_tags) {
- /*
- * With max_cahe and batch set to 1, the allocator fallbacks to
- * no cached. It's fine reserved tags allocation is slow.
- */
- ret = __percpu_ida_init(&tags->reserved_tags, reserved_tags,
- 1, 1);
- if (ret)
- goto err_reserved_tags;
- }
+void blk_mq_free_tags(struct blk_mq_tags *tags)
+{
+ bt_free(&tags->bitmap_tags);
+ bt_free(&tags->breserved_tags);
+ kfree(tags);
+}
- return 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;
-err_reserved_tags:
- percpu_ida_destroy(&tags->free_tags);
-err_free_tags:
- kfree(tags);
- return NULL;
+ *tag = prandom_u32() % depth;
}
-void blk_mq_free_tags(struct blk_mq_tags *tags)
+int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
{
- percpu_ida_destroy(&tags->free_tags);
- percpu_ida_destroy(&tags->reserved_tags);
- kfree(tags);
+ 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 cpu;
+ unsigned int free, res;
if (!tags)
return 0;
- page += sprintf(page, "nr_tags=%u, reserved_tags=%u, batch_move=%u,"
- " max_cache=%u\n", tags->nr_tags, tags->nr_reserved_tags,
- tags->nr_batch_move, tags->nr_max_cache);
+ 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);
- page += sprintf(page, "nr_free=%u, nr_reserved=%u\n",
- percpu_ida_free_tags(&tags->free_tags, nr_cpu_ids),
- percpu_ida_free_tags(&tags->reserved_tags, nr_cpu_ids));
+ free = bt_unused_tags(&tags->bitmap_tags);
+ res = bt_unused_tags(&tags->breserved_tags);
- for_each_possible_cpu(cpu) {
- page += sprintf(page, " cpu%02u: nr_free=%u\n", cpu,
- percpu_ida_free_tags(&tags->free_tags, cpu));
- }
+ 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;
}
projects / cascardo / linux.git / blobdiff