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authorUros Bizjak <ubizjak@gmail.com>2022-09-08 18:12:00 +0300
committerJens Axboe <axboe@kernel.dk>2022-09-08 18:22:42 +0300
commitc35227d4e8cbc70a6622cc7cc5f8c3bff513f1fa (patch)
tree2cf72382f2a2bbedf515081f5fb6d4513742b82a /lib
parent1de7c3cf48fc41cd95adb12bd1ea9033a917798a (diff)
downloadlinux-c35227d4e8cbc70a6622cc7cc5f8c3bff513f1fa.tar.xz
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 <axboe@kernel.dk> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Link: https://lore.kernel.org/r/20220908151200.9993-1-ubizjak@gmail.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'lib')
-rw-r--r--lib/sbitmap.c10
1 files 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,