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Subject[PATCH v2 1/4] sbitmap: optimise sbitmap_deferred_clear()
Date
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.
Pass in sbitmap_word instead of {sb, index}, so it's cached in a
variable. It also improves code generation of
sbitmap_find_bit_in_index().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
lib/sbitmap.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 267aa7709416..c1c8a4e69325 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -12,32 +12,32 @@
/*
* See if we have deferred clears that we can batch move
*/
-static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
+static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
{
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;
}

@@ -92,7 +92,7 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
unsigned int i;

for (i = 0; i < sb->map_nr; i++)
- sbitmap_deferred_clear(sb, i);
+ sbitmap_deferred_clear(&sb->map[i]);

sb->depth = depth;
sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
@@ -139,15 +139,15 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
static int sbitmap_find_bit_in_index(struct sbitmap *sb, int index,
unsigned int alloc_hint, bool round_robin)
{
+ struct sbitmap_word *map = &sb->map[index];
int nr;

do {
- nr = __sbitmap_get_word(&sb->map[index].word,
- sb->map[index].depth, alloc_hint,
+ nr = __sbitmap_get_word(&map->word, map->depth, alloc_hint,
!round_robin);
if (nr != -1)
break;
- if (!sbitmap_deferred_clear(sb, index))
+ if (!sbitmap_deferred_clear(map))
break;
} while (1);

@@ -207,7 +207,7 @@ int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
break;
}

- if (sbitmap_deferred_clear(sb, index))
+ if (sbitmap_deferred_clear(&sb->map[index]))
goto again;

/* Jump to next index. */
--
2.24.0
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