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author | Jens Axboe <axboe@fb.com> | 2014-05-09 19:41:15 (GMT) |
---|---|---|
committer | Jens Axboe <axboe@fb.com> | 2014-05-09 19:41:15 (GMT) |
commit | 59d13bf5f57ded658c872fa22276f75ab8f12841 (patch) | |
tree | ea3b3bf9395c01a5443c2e01874837a19d6e4c62 /block | |
parent | 4bb659b156996f2993dc16fad71fec9ee070153c (diff) | |
download | linux-59d13bf5f57ded658c872fa22276f75ab8f12841.tar.xz |
blk-mq: use sparser tag layout for lower queue depth
For best performance, spreading tags over multiple cachelines
makes the tagging more efficient on multicore systems. But since
we have 8 * sizeof(unsigned long) tags per cacheline, we don't
always get a nice spread.
Attempt to spread the tags over at least 4 cachelines, using fewer
number of bits per unsigned long if we have to. This improves
tagging performance in setups with 32-128 tags. For higher depths,
the spread is the same as before (BITS_PER_LONG tags per cacheline).
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block')
-rw-r--r-- | block/blk-mq-tag.c | 45 | ||||
-rw-r--r-- | block/blk-mq-tag.h | 7 |
2 files changed, 36 insertions, 16 deletions
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 467f3a2..6c78c08 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -44,7 +44,7 @@ static int __bt_get_word(struct blk_mq_bitmap *bm, unsigned int last_tag) { int tag, org_last_tag, end; - org_last_tag = last_tag = TAG_TO_BIT(last_tag); + org_last_tag = last_tag; end = bm->depth; do { restart: @@ -84,12 +84,12 @@ static int __bt_get(struct blk_mq_bitmap_tags *bt, unsigned int *tag_cache) int index, i, tag; last_tag = org_last_tag = *tag_cache; - index = TAG_TO_INDEX(last_tag); + index = TAG_TO_INDEX(bt, last_tag); for (i = 0; i < bt->map_nr; i++) { - tag = __bt_get_word(&bt->map[index], last_tag); + tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag)); if (tag != -1) { - tag += index * BITS_PER_LONG; + tag += (index << bt->bits_per_word); goto done; } @@ -233,10 +233,10 @@ static struct bt_wait_state *bt_wake_ptr(struct blk_mq_bitmap_tags *bt) static void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag) { - const int index = TAG_TO_INDEX(tag); + const int index = TAG_TO_INDEX(bt, tag); struct bt_wait_state *bs; - clear_bit(TAG_TO_BIT(tag), &bt->map[index].word); + clear_bit(TAG_TO_BIT(bt, tag), &bt->map[index].word); bs = bt_wake_ptr(bt); if (bs && atomic_dec_and_test(&bs->wait_cnt)) { @@ -292,7 +292,7 @@ static void bt_for_each_free(struct blk_mq_bitmap_tags *bt, bit++; } while (1); - off += BITS_PER_LONG; + off += (1 << bt->bits_per_word); } } @@ -333,14 +333,31 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth, { 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) { - int nr, i, map_depth; + unsigned int nr, i, map_depth, 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, BITS_PER_LONG) / BITS_PER_LONG; + nr = ALIGN(depth, tags_per_word) / tags_per_word; bt->map = kzalloc_node(nr * sizeof(struct blk_mq_bitmap), GFP_KERNEL, node); if (!bt->map) @@ -349,8 +366,8 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth, bt->map_nr = nr; map_depth = depth; for (i = 0; i < nr; i++) { - bt->map[i].depth = min(map_depth, BITS_PER_LONG); - map_depth -= BITS_PER_LONG; + bt->map[i].depth = min(map_depth, tags_per_word); + map_depth -= tags_per_word; } } @@ -443,8 +460,10 @@ ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page) if (!tags) return 0; - page += sprintf(page, "nr_tags=%u, reserved_tags=%u\n", - tags->nr_tags, tags->nr_reserved_tags); + 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); diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h index 06d4a2f..7aa9f06 100644 --- a/block/blk-mq-tag.h +++ b/block/blk-mq-tag.h @@ -11,8 +11,8 @@ struct bt_wait_state { wait_queue_head_t wait; } ____cacheline_aligned_in_smp; -#define TAG_TO_INDEX(tag) ((tag) / BITS_PER_LONG) -#define TAG_TO_BIT(tag) ((tag) & (BITS_PER_LONG - 1)) +#define TAG_TO_INDEX(bt, tag) ((tag) >> (bt)->bits_per_word) +#define TAG_TO_BIT(bt, tag) ((tag) & ((1 << (bt)->bits_per_word) - 1)) struct blk_mq_bitmap { unsigned long word; @@ -22,9 +22,10 @@ struct blk_mq_bitmap { struct blk_mq_bitmap_tags { unsigned int depth; unsigned int wake_cnt; + unsigned int bits_per_word; - struct blk_mq_bitmap *map; unsigned int map_nr; + struct blk_mq_bitmap *map; unsigned int wake_index; struct bt_wait_state *bs; |