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| author | Pavel Begunkov <asml.silence@gmail.com> | 2020-11-22 16:35:47 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2020-12-08 01:12:49 +0100 |
| commit | c3250c8d2451ffbea14ba95164c59edd943ee4be (patch) | |
| tree | d15f81f25f233c6576b615fdf44bdf77c3bc4696 | |
| parent | sbitmap: remove swap_lock (diff) | |
| download | linux-c3250c8d2451ffbea14ba95164c59edd943ee4be.tar.xz linux-c3250c8d2451ffbea14ba95164c59edd943ee4be.zip | |
sbitmap: replace CAS with atomic and
sbitmap_deferred_clear() does CAS loop to propagate cleared bits,
replace it with equivalent atomic bitwise and. That's slightly faster
and makes wait-free instead of lock-free as before.
The atomic can be relaxed (i.e. barrier-less) because following
sbitmap_get*() deal with synchronisation, see comments in
sbitmap_queue_clear().
It's ok to cast to atomic_long_t, that's what bitops/lock.h does.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | lib/sbitmap.c | 8 |
1 files changed, 3 insertions, 5 deletions
diff --git a/lib/sbitmap.c b/lib/sbitmap.c index 4fd877048ba8..c18b518a16ba 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -14,7 +14,7 @@ */ static inline bool sbitmap_deferred_clear(struct sbitmap_word *map) { - unsigned long mask, val; + unsigned long mask; if (!READ_ONCE(map->cleared)) return false; @@ -27,10 +27,8 @@ static inline bool sbitmap_deferred_clear(struct sbitmap_word *map) /* * Now clear the masked bits in our free word */ - do { - val = map->word; - } while (cmpxchg(&map->word, val, val & ~mask) != val); - + atomic_long_andnot(mask, (atomic_long_t *)&map->word); + BUILD_BUG_ON(sizeof(atomic_long_t) != sizeof(map->word)); return true; } |