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| author | Uros Bizjak <ubizjak@gmail.com> | 2022-09-08 17:12:00 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2022-09-08 17:22:42 +0200 |
| commit | c35227d4e8cbc70a6622cc7cc5f8c3bff513f1fa (patch) | |
| tree | 2cf72382f2a2bbedf515081f5fb6d4513742b82a /lib/sbitmap.c | |
| parent | nbd: Fix hung when signal interrupts nbd_start_device_ioctl() (diff) | |
| download | linux-c35227d4e8cbc70a6622cc7cc5f8c3bff513f1fa.tar.xz linux-c35227d4e8cbc70a6622cc7cc5f8c3bff513f1fa.zip | |
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 '')
| -rw-r--r-- | lib/sbitmap.c | 10 |
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, |