From c35227d4e8cbc70a6622cc7cc5f8c3bff513f1fa Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Thu, 8 Sep 2022 17:12:00 +0200 Subject: sbitmap: Use atomic_long_try_cmpxchg in __sbitmap_queue_get_batch Use atomic_long_try_cmpxchg instead of atomic_long_cmpxchg (*ptr, old, new) == old in __sbitmap_queue_get_batch. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, atomic_long_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications, e.g. an extra memory read can be avoided in the loop. No functional change intended. Cc: Jens Axboe Signed-off-by: Uros Bizjak Link: https://lore.kernel.org/r/20220908151200.9993-1-ubizjak@gmail.com Signed-off-by: Jens Axboe --- lib/sbitmap.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index 47cd8fb894ba..cbfd2e677d87 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -533,16 +533,16 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags, nr = find_first_zero_bit(&map->word, map_depth); if (nr + nr_tags <= map_depth) { atomic_long_t *ptr = (atomic_long_t *) &map->word; - unsigned long val, ret; + unsigned long val; get_mask = ((1UL << nr_tags) - 1) << nr; + val = READ_ONCE(map->word); do { - val = READ_ONCE(map->word); if ((val & ~get_mask) != val) goto next; - ret = atomic_long_cmpxchg(ptr, val, get_mask | val); - } while (ret != val); - get_mask = (get_mask & ~ret) >> nr; + } while (!atomic_long_try_cmpxchg(ptr, &val, + get_mask | val)); + get_mask = (get_mask & ~val) >> nr; if (get_mask) { *offset = nr + (index << sb->shift); update_alloc_hint_after_get(sb, depth, hint, -- cgit v1.2.3