Initial import

1 files changed, 666 insertions, 0 deletions

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
new file mode 100644
index 000000000..be3290cc0
--- /dev/null
+++ b/block/blk-mq-tag.c
@@ -0,0 +1,666 @@
+/*
+ * 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,
+			 bool nowrap)
+{
+	int tag, org_last_tag = last_tag;
+
+	while (1) {
+		tag = find_next_zero_bit(&bm->word, bm->depth, last_tag);
+		if (unlikely(tag >= bm->depth)) {
+			/*
+			 * We started with an offset, and we didn't reset the
+			 * offset to 0 in a failure case, so start from 0 to
+			 * exhaust the map.
+			 */
+			if (org_last_tag && last_tag && !nowrap) {
+				last_tag = org_last_tag = 0;
+				continue;
+			}
+			return -1;
+		}
+
+		if (!test_and_set_bit(tag, &bm->word))
+			break;
+
+		last_tag = tag + 1;
+		if (last_tag >= bm->depth - 1)
+			last_tag = 0;
+	}
+
+	return tag;
+}
+
+#define BT_ALLOC_RR(tags) (tags->alloc_policy == BLK_TAG_ALLOC_RR)
+
+/*
+ * 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, struct blk_mq_tags *tags)
+{
+	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),
+				    BT_ALLOC_RR(tags));
+		if (tag != -1) {
+			tag += (index << bt->bits_per_word);
+			goto done;
+		}
+
+		/*
+		 * Jump to next index, and reset the last tag to be the
+		 * first tag of that index
+		 */
+		index++;
+		last_tag = (index << bt->bits_per_word);
+
+		if (index >= bt->map_nr) {
+			index = 0;
+			last_tag = 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 || unlikely(BT_ALLOC_RR(tags))) {
+		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 blk_mq_tags *tags)
+{
+	struct bt_wait_state *bs;
+	DEFINE_WAIT(wait);
+	int tag;
+
+	tag = __bt_get(hctx, bt, last_tag, tags);
+	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, tags);
+		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. Note that hctx can be NULL here for
+		 * reserved tag allocation.
+		 */
+		if (hctx)
+			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, tags);
+		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, data->hctx->tags);
+	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,
+		data->hctx->tags);
+	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);
+		if (likely(tags->alloc_policy == BLK_TAG_ALLOC_FIFO))
+			*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);
+		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, int alloc_policy)
+{
+	unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
+
+	tags->alloc_policy = alloc_policy;
+
+	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, int alloc_policy)
+{
+	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, alloc_policy);
+}
+
+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;
+}