From b904a7991802d2fba1f8c59e6f0790021342c0ff Mon Sep 17 00:00:00 2001
From: Kent Overstreet <kent.overstreet@gmail.com>
Date: Wed, 6 Nov 2019 19:40:09 -0500
Subject: [PATCH] bcachefs: Go back to 16 bit mantissa bkey floats
The previous optimizations means using 32 bit mantissas are now a net
loss - having bkey_float be only 4 bytes is good for prefetching.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
fs/bcachefs/bset.c | 99 +++++++++++++---------------------------------
1 file changed, 28 insertions(+), 71 deletions(-)
diff --git a/fs/bcachefs/bset.c b/fs/bcachefs/bset.c
index 5b6e29b65f5b0..af20b98036085 100644
--- a/fs/bcachefs/bset.c
+++ b/fs/bcachefs/bset.c
@@ -285,33 +285,20 @@ static inline void bch2_btree_node_iter_next_check(struct btree_node_iter *iter,
#define BFLOAT_FAILED_UNPACKED U8_MAX
#define BFLOAT_FAILED U8_MAX
-#define KEY_WORDS BITS_TO_LONGS(1 << BKEY_EXPONENT_BITS)
-
struct bkey_float {
u8 exponent;
u8 key_offset;
- union {
- u32 mantissa32;
- struct {
- u16 mantissa16;
- u16 _pad;
- };
- };
-} __packed;
-
-#define BFLOAT_32BIT_NR 32U
+ u16 mantissa;
+};
+#define BKEY_MANTISSA_BITS 16
static unsigned bkey_float_byte_offset(unsigned idx)
{
- int d = (idx - BFLOAT_32BIT_NR) << 1;
-
- d &= ~(d >> 31);
-
- return idx * 6 - d;
+ return idx * sizeof(struct bkey_float);
}
struct ro_aux_tree {
- struct bkey_float _d[0];
+ struct bkey_float f[0];
};
struct rw_aux_tree {
@@ -366,8 +353,8 @@ static unsigned bset_aux_tree_buf_end(const struct bset_tree *t)
return t->aux_data_offset;
case BSET_RO_AUX_TREE:
return t->aux_data_offset +
- DIV_ROUND_UP(bkey_float_byte_offset(t->size) +
- sizeof(u8) * t->size, 8);
+ DIV_ROUND_UP(t->size * sizeof(struct bkey_float) +
+ t->size * sizeof(u8), 8);
case BSET_RW_AUX_TREE:
return t->aux_data_offset +
DIV_ROUND_UP(sizeof(struct rw_aux_tree) * t->size, 8);
@@ -406,17 +393,11 @@ static u8 *ro_aux_tree_prev(const struct btree *b,
return __aux_tree_base(b, t) + bkey_float_byte_offset(t->size);
}
-static struct bkey_float *bkey_float_get(struct ro_aux_tree *b,
- unsigned idx)
-{
- return (void *) b + bkey_float_byte_offset(idx);
-}
-
static struct bkey_float *bkey_float(const struct btree *b,
const struct bset_tree *t,
unsigned idx)
{
- return bkey_float_get(ro_aux_tree_base(b, t), idx);
+ return ro_aux_tree_base(b, t)->f + idx;
}
static void bset_aux_tree_verify(struct btree *b)
@@ -650,21 +631,6 @@ static unsigned rw_aux_tree_bsearch(struct btree *b,
return idx;
}
-static inline unsigned bfloat_mantissa(const struct bkey_float *f,
- unsigned idx)
-{
- return idx < BFLOAT_32BIT_NR ? f->mantissa32 : f->mantissa16;
-}
-
-static inline void bfloat_mantissa_set(struct bkey_float *f,
- unsigned idx, unsigned mantissa)
-{
- if (idx < BFLOAT_32BIT_NR)
- f->mantissa32 = mantissa;
- else
- f->mantissa16 = mantissa;
-}
-
static inline unsigned bkey_mantissa(const struct bkey_packed *k,
const struct bkey_float *f,
unsigned idx)
@@ -684,9 +650,9 @@ static inline unsigned bkey_mantissa(const struct bkey_packed *k,
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
v >>= f->exponent & 7;
#else
- v >>= 64 - (f->exponent & 7) - (idx < BFLOAT_32BIT_NR ? 32 : 16);
+ v >>= 64 - (f->exponent & 7) - BKEY_MANTISSA_BITS;
#endif
- return idx < BFLOAT_32BIT_NR ? (u32) v : (u16) v;
+ return (u16) v;
}
static void make_bfloat(struct btree *b, struct bset_tree *t,
@@ -697,7 +663,6 @@ static void make_bfloat(struct btree *b, struct bset_tree *t,
struct bkey_float *f = bkey_float(b, t, j);
struct bkey_packed *m = tree_to_bkey(b, t, j);
struct bkey_packed *l, *r;
- unsigned bits = j < BFLOAT_32BIT_NR ? 32 : 16;
unsigned mantissa;
int shift, exponent, high_bit;
@@ -759,8 +724,8 @@ static void make_bfloat(struct btree *b, struct bset_tree *t,
* of the key: we handle this later:
*/
high_bit = max(bch2_bkey_greatest_differing_bit(b, l, r),
- min_t(unsigned, bits, b->nr_key_bits) - 1);
- exponent = high_bit - (bits - 1);
+ min_t(unsigned, BKEY_MANTISSA_BITS, b->nr_key_bits) - 1);
+ exponent = high_bit - (BKEY_MANTISSA_BITS - 1);
/*
* Then we calculate the actual shift value, from the start of the key
@@ -769,12 +734,12 @@ static void make_bfloat(struct btree *b, struct bset_tree *t,
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
shift = (int) (b->format.key_u64s * 64 - b->nr_key_bits) + exponent;
- EBUG_ON(shift + bits > b->format.key_u64s * 64);
+ EBUG_ON(shift + BKEY_MANTISSA_BITS > b->format.key_u64s * 64);
#else
shift = high_bit_offset +
b->nr_key_bits -
exponent -
- bits;
+ BKEY_MANTISSA_BITS;
EBUG_ON(shift < KEY_PACKED_BITS_START);
#endif
@@ -790,7 +755,7 @@ static void make_bfloat(struct btree *b, struct bset_tree *t,
if (exponent < 0)
mantissa |= ~(~0U << -exponent);
- bfloat_mantissa_set(f, j, mantissa);
+ f->mantissa = mantissa;
}
/* bytes remaining - only valid for last bset: */
@@ -803,14 +768,8 @@ static unsigned __bset_tree_capacity(struct btree *b, struct bset_tree *t)
static unsigned bset_ro_tree_capacity(struct btree *b, struct bset_tree *t)
{
- unsigned bytes = __bset_tree_capacity(b, t);
-
- if (bytes < 7 * BFLOAT_32BIT_NR)
- return bytes / 7;
-
- bytes -= 7 * BFLOAT_32BIT_NR;
-
- return BFLOAT_32BIT_NR + bytes / 5;
+ return __bset_tree_capacity(b, t) /
+ (sizeof(struct bkey_float) + sizeof(u8));
}
static unsigned bset_rw_tree_capacity(struct btree *b, struct bset_tree *t)
@@ -1309,9 +1268,8 @@ static inline bool bkey_mantissa_bits_dropped(const struct btree *b,
return f->exponent > key_bits_start;
#else
unsigned key_bits_end = high_bit_offset + b->nr_key_bits;
- unsigned mantissa_bits = n < BFLOAT_32BIT_NR ? 32 : 16;
- return f->exponent + mantissa_bits < key_bits_end;
+ return f->exponent + BKEY_MANTISSA_BITS < key_bits_end;
#endif
}
@@ -1329,16 +1287,16 @@ static struct bkey_packed *bset_search_tree(const struct btree *b,
do {
if (likely(n << 4 < t->size))
- prefetch(bkey_float_get(base, n << 4));
+ prefetch(&base->f[n << 4]);
- f = bkey_float_get(base, n);
+ f = &base->f[n];
if (!unlikely(packed_search))
goto slowpath;
if (unlikely(f->exponent >= BFLOAT_FAILED))
goto slowpath;
- l = bfloat_mantissa(f, n);
+ l = f->mantissa;
r = bkey_mantissa(packed_search, f, n);
if (unlikely(l == r) && bkey_mantissa_bits_dropped(b, f, n))
@@ -1361,16 +1319,15 @@ slowpath:
* n would have been the node we recursed to - the low bit tells us if
* we recursed left or recursed right.
*/
- if (n & 1) {
- return cacheline_to_bkey(b, t, inorder, f->key_offset);
- } else {
- if (--inorder) {
- n = eytzinger1_prev(n >> 1, t->size);
- f = bkey_float_get(base, n);
- return cacheline_to_bkey(b, t, inorder, f->key_offset);
- } else
+ if (likely(!(n & 1))) {
+ --inorder;
+ if (unlikely(!inorder))
return btree_bkey_first(b, t);
+
+ f = &base->f[eytzinger1_prev(n >> 1, t->size)];
}
+
+ return cacheline_to_bkey(b, t, inorder, f->key_offset);
}
static __always_inline __flatten
--
2.30.2