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 1/2] sbitmap: optimise sbitmap_deferred_clear()
Date: Sat, 21 Nov 2020 00:01:15 +0000 [thread overview]
Message-ID: <9b17f6db792526413e368dbb72bf7aca12b327d3.1605908165.git.asml.silence@gmail.com> (raw)
In-Reply-To: <cover.1605908165.git.asml.silence@gmail.com>
Because of spinlocks and atomics sbitmap_deferred_clear() have to reload
&sb->map[index] on each access even though the map address won't change.
Hint it by explicitly caching it in a variable.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
lib/sbitmap.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 267aa7709416..49afb34e8340 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -14,30 +14,31 @@
*/
static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
{
+ struct sbitmap_word *map = &sb->map[index];
unsigned long mask, val;
bool ret = false;
unsigned long flags;
- spin_lock_irqsave(&sb->map[index].swap_lock, flags);
+ spin_lock_irqsave(&map->swap_lock, flags);
- if (!sb->map[index].cleared)
+ if (!map->cleared)
goto out_unlock;
/*
* First get a stable cleared mask, setting the old mask to 0.
*/
- mask = xchg(&sb->map[index].cleared, 0);
+ mask = xchg(&map->cleared, 0);
/*
* Now clear the masked bits in our free word
*/
do {
- val = sb->map[index].word;
- } while (cmpxchg(&sb->map[index].word, val, val & ~mask) != val);
+ val = map->word;
+ } while (cmpxchg(&map->word, val, val & ~mask) != val);
ret = true;
out_unlock:
- spin_unlock_irqrestore(&sb->map[index].swap_lock, flags);
+ spin_unlock_irqrestore(&map->swap_lock, flags);
return ret;
}
--
2.24.0
next prev parent reply other threads:[~2020-11-21 0:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-21 0:01 [PATCH for-next 0/2] optimise sbitmap deferred clear Pavel Begunkov
2020-11-21 0:01 ` Pavel Begunkov [this message]
2020-11-21 0:01 ` [PATCH 2/2] sbitmap: remove swap_lock Pavel Begunkov
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