diff options
Diffstat (limited to 'block/bfq-iosched.c')
| -rw-r--r-- | block/bfq-iosched.c | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index f352b1677143..a7ab0cb50733 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -417,6 +417,82 @@ static struct request *bfq_choose_req(struct bfq_data *bfqd, } } +/* + * See the comments on bfq_limit_depth for the purpose of + * the depths set in the function. + */ +static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt) +{ + bfqd->sb_shift = bt->sb.shift; + + /* + * In-word depths if no bfq_queue is being weight-raised: + * leaving 25% of tags only for sync reads. + * + * In next formulas, right-shift the value + * (1U<<bfqd->sb_shift), instead of computing directly + * (1U<<(bfqd->sb_shift - something)), to be robust against + * any possible value of bfqd->sb_shift, without having to + * limit 'something'. + */ + /* no more than 50% of tags for async I/O */ + bfqd->word_depths[0][0] = max((1U<<bfqd->sb_shift)>>1, 1U); + /* + * no more than 75% of tags for sync writes (25% extra tags + * w.r.t. async I/O, to prevent async I/O from starving sync + * writes) + */ + bfqd->word_depths[0][1] = max(((1U<<bfqd->sb_shift) * 3)>>2, 1U); + + /* + * In-word depths in case some bfq_queue is being weight- + * raised: leaving ~63% of tags for sync reads. This is the + * highest percentage for which, in our tests, application + * start-up times didn't suffer from any regression due to tag + * shortage. + */ + /* no more than ~18% of tags for async I/O */ + bfqd->word_depths[1][0] = max(((1U<<bfqd->sb_shift) * 3)>>4, 1U); + /* no more than ~37% of tags for sync writes (~20% extra tags) */ + bfqd->word_depths[1][1] = max(((1U<<bfqd->sb_shift) * 6)>>4, 1U); +} + +/* + * Async I/O can easily starve sync I/O (both sync reads and sync + * writes), by consuming all tags. Similarly, storms of sync writes, + * such as those that sync(2) may trigger, can starve sync reads. + * Limit depths of async I/O and sync writes so as to counter both + * problems. + */ +static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data) +{ + struct blk_mq_tags *tags = blk_mq_tags_from_data(data); + struct bfq_data *bfqd = data->q->elevator->elevator_data; + struct sbitmap_queue *bt; + + if (op_is_sync(op) && !op_is_write(op)) + return; + + if (data->flags & BLK_MQ_REQ_RESERVED) { + if (unlikely(!tags->nr_reserved_tags)) { + WARN_ON_ONCE(1); + return; + } + bt = &tags->breserved_tags; + } else + bt = &tags->bitmap_tags; + + if (unlikely(bfqd->sb_shift != bt->sb.shift)) + bfq_update_depths(bfqd, bt); + + data->shallow_depth = + bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)]; + + bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u", + __func__, bfqd->wr_busy_queues, op_is_sync(op), + data->shallow_depth); +} + static struct bfq_queue * bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root, sector_t sector, struct rb_node **ret_parent, @@ -5285,6 +5361,7 @@ static struct elv_fs_entry bfq_attrs[] = { static struct elevator_type iosched_bfq_mq = { .ops.mq = { + .limit_depth = bfq_limit_depth, .prepare_request = bfq_prepare_request, .finish_request = bfq_finish_request, .exit_icq = bfq_exit_icq, |