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bcachefs: Go back to 16 bit mantissa bkey floats

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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>
This commit is contained in:
Kent Overstreet 2019-11-06 19:40:09 -05:00 committed by Kent Overstreet
parent 58404bb236
commit b904a79918
1 changed files with 28 additions and 71 deletions
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99
fs/bcachefs/bset.c
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@ -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 @@ static struct bkey_packed *bset_search_tree(const struct btree *b,
* 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