From 42e6c6ce03fd3e41e39a0f93f9b1a1d9fa664338 Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Thu, 7 Aug 2025 11:24:12 +0800 Subject: lib/sbitmap: convert shallow_depth from one word to the whole sbitmap Currently elevators will record internal 'async_depth' to throttle asynchronous requests, and they both calculate shallow_dpeth based on sb->shift, with the respect that sb->shift is the available tags in one word. However, sb->shift is not the availbale tags in the last word, see __map_depth: if (index == sb->map_nr - 1) return sb->depth - (index << sb->shift); For consequence, if the last word is used, more tags can be get than expected, for example, assume nr_requests=256 and there are four words, in the worst case if user set nr_requests=32, then the first word is the last word, and still use bits per word, which is 64, to calculate async_depth is wrong. One the ohter hand, due to cgroup qos, bfq can allow only one request to be allocated, and set shallow_dpeth=1 will still allow the number of words request to be allocated. Fix this problems by using shallow_depth to the whole sbitmap instead of per word, also change kyber, mq-deadline and bfq to follow this, a new helper __map_depth_with_shallow() is introduced to calculate available bits in each word. Signed-off-by: Yu Kuai Link: https://lore.kernel.org/r/20250807032413.1469456-2-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe --- lib/sbitmap.c | 56 +++++++++++++++++++++++++++++--------------------------- 1 file changed, 29 insertions(+), 27 deletions(-) (limited to 'lib/sbitmap.c') diff --git a/lib/sbitmap.c b/lib/sbitmap.c index d3412984170c03..c07e3cd82e29d7 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -208,8 +208,28 @@ static int sbitmap_find_bit_in_word(struct sbitmap_word *map, return nr; } +static unsigned int __map_depth_with_shallow(const struct sbitmap *sb, + int index, + unsigned int shallow_depth) +{ + u64 shallow_word_depth; + unsigned int word_depth, reminder; + + word_depth = __map_depth(sb, index); + if (shallow_depth >= sb->depth) + return word_depth; + + shallow_word_depth = word_depth * shallow_depth; + reminder = do_div(shallow_word_depth, sb->depth); + + if (reminder >= (index + 1) * word_depth) + shallow_word_depth++; + + return (unsigned int)shallow_word_depth; +} + static int sbitmap_find_bit(struct sbitmap *sb, - unsigned int depth, + unsigned int shallow_depth, unsigned int index, unsigned int alloc_hint, bool wrap) @@ -218,12 +238,12 @@ static int sbitmap_find_bit(struct sbitmap *sb, int nr = -1; for (i = 0; i < sb->map_nr; i++) { - nr = sbitmap_find_bit_in_word(&sb->map[index], - min_t(unsigned int, - __map_depth(sb, index), - depth), - alloc_hint, wrap); + unsigned int depth = __map_depth_with_shallow(sb, index, + shallow_depth); + if (depth) + nr = sbitmap_find_bit_in_word(&sb->map[index], depth, + alloc_hint, wrap); if (nr != -1) { nr += index << sb->shift; break; @@ -406,27 +426,9 @@ EXPORT_SYMBOL_GPL(sbitmap_bitmap_show); static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq, unsigned int depth) { - unsigned int wake_batch; - unsigned int shallow_depth; - - /* - * Each full word of the bitmap has bits_per_word bits, and there might - * be a partial word. There are depth / bits_per_word full words and - * depth % bits_per_word bits left over. In bitwise arithmetic: - * - * bits_per_word = 1 << shift - * depth / bits_per_word = depth >> shift - * depth % bits_per_word = depth & ((1 << shift) - 1) - * - * Each word can be limited to sbq->min_shallow_depth bits. - */ - shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth); - depth = ((depth >> sbq->sb.shift) * shallow_depth + - min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth)); - wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1, - SBQ_WAKE_BATCH); - - return wake_batch; + return clamp_t(unsigned int, + min(depth, sbq->min_shallow_depth) / SBQ_WAIT_QUEUES, + 1, SBQ_WAKE_BATCH); } int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth, -- cgit 1.2.3-korg