From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Omar Sandoval <osandov@osandov.com>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH v2 3/4] sbitmap: replace CAS with atomic and
Date: Sun, 22 Nov 2020 15:35:47 +0000 [thread overview]
Message-ID: <6c9b6664bcd12faa9d1a9969a32774a75d1d316f.1606058975.git.asml.silence@gmail.com> (raw)
In-Reply-To: <cover.1606058975.git.asml.silence@gmail.com>
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>
---
lib/sbitmap.c | 8 +++-----
1 file 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;
}
--
2.24.0
next prev parent reply other threads:[~2020-11-22 15:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-22 15:35 [PATCH v2 for-next 0/4] optimise sbitmap deferred clear Pavel Begunkov
2020-11-22 15:35 ` [PATCH v2 1/4] sbitmap: optimise sbitmap_deferred_clear() Pavel Begunkov
2020-11-24 14:11 ` John Garry
2020-11-24 15:01 ` Pavel Begunkov
2020-11-22 15:35 ` [PATCH v2 2/4] sbitmap: remove swap_lock Pavel Begunkov
2020-11-24 14:22 ` John Garry
2020-11-24 14:43 ` Pavel Begunkov
2020-11-26 2:46 ` Ming Lei
2020-11-26 13:44 ` Pavel Begunkov
2020-11-27 2:06 ` Ming Lei
2020-11-22 15:35 ` Pavel Begunkov [this message]
2020-11-22 15:35 ` [PATCH v2 4/4] sbitmap: simplify wrap check Pavel Begunkov
2020-12-08 0:13 ` [PATCH v2 for-next 0/4] optimise sbitmap deferred clear Jens Axboe
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