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When bitpos can't be implemented with an inline ffs* instruction,

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change the binary search so that it does not depend on a single bit
only being set in the bitmask. Use bitpos more generally, and avoid
some clearing of bits to accommodate its current behavior.

Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20237
This commit is contained in:
Doug Moore 2019-05-11 09:09:10 +00:00
parent 81b3b91e6b
commit 535192530c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=347484
1 changed files with 35 additions and 26 deletions
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61
sys/kern/subr_blist.c
View file

@ -192,30 +192,40 @@ bitrange(int n, int count)
/*
* Use binary search, or a faster method, to find the 1 bit in a u_daddr_t.
* Assumes that the argument has only one bit set.
* Find the first bit set in a u_daddr_t.
*/
static inline int
generic_bitpos(u_daddr_t mask)
{
int hi, lo, mid;
lo = 0;
hi = BLIST_BMAP_RADIX;
while (lo + 1 < hi) {
mid = (lo + hi) >> 1;
if (mask & bitrange(0, mid))
hi = mid;
else
lo = mid;
}
return (lo);
}
static inline int
bitpos(u_daddr_t mask)
{
int hi, lo, mid;
switch (sizeof(mask)) {
#ifdef HAVE_INLINE_FFSLL
case sizeof(long long):
return (ffsll(mask) - 1);
#endif
#ifdef HAVE_INLINE_FFS
case sizeof(int):
return (ffs(mask) - 1);
#endif
default:
lo = 0;
hi = BLIST_BMAP_RADIX;
while (lo + 1 < hi) {
mid = (lo + hi) >> 1;
if ((mask >> mid) != 0)
lo = mid;
else
hi = mid;
}
return (lo);
return (generic_bitpos(mask));
}
}
@ -532,7 +542,8 @@ blist_stats(blist_t bl, struct sbuf *s)
struct gap_stats gstats;
struct gap_stats *stats = &gstats;
daddr_t i, nodes, radix;
u_daddr_t bit, diff, mask;
u_daddr_t diff, mask;
int digit;
init_gap_stats(stats);
nodes = 0;
@ -570,9 +581,9 @@ blist_stats(blist_t bl, struct sbuf *s)
if (gap_stats_counting(stats))
diff ^= 1;
while (diff != 0) {
bit = diff & -diff;
update_gap_stats(stats, i + bitpos(bit));
diff ^= bit;
digit = bitpos(diff);
update_gap_stats(stats, i + digit);
diff ^= bitrange(digit, 1);
}
}
nodes += radix_to_skip(radix);
@ -776,7 +787,7 @@ static daddr_t
blst_meta_alloc(blmeta_t *scan, daddr_t cursor, daddr_t count, u_daddr_t radix)
{
daddr_t blk, i, r, skip;
u_daddr_t bit, mask;
u_daddr_t mask;
bool scan_from_start;
int digit;
@ -808,8 +819,7 @@ blst_meta_alloc(blmeta_t *scan, daddr_t cursor, daddr_t count, u_daddr_t radix)
* Examine the nonempty subtree associated with each bit set in mask.
*/
do {
bit = mask & -mask;
digit = bitpos(bit);
digit = bitpos(mask);
i = 1 + digit * skip;
if (count <= scan[i].bm_bighint) {
/*
@ -819,12 +829,12 @@ blst_meta_alloc(blmeta_t *scan, daddr_t cursor, daddr_t count, u_daddr_t radix)
count, radix);
if (r != SWAPBLK_NONE) {
if (scan[i].bm_bitmap == 0)
scan->bm_bitmap ^= bit;
scan->bm_bitmap ^= bitrange(digit, 1);
return (r);
}
}
cursor = blk;
} while ((mask ^= bit) != 0);
} while ((mask ^= bitrange(digit, 1)) != 0);
/*
* We couldn't allocate count in this subtree. If the whole tree was
@ -1019,7 +1029,7 @@ static void
blst_radix_print(blmeta_t *scan, daddr_t blk, daddr_t radix, int tab)
{
daddr_t skip;
u_daddr_t bit, mask;
u_daddr_t mask;
int digit;
if (radix == BLIST_BMAP_RADIX) {
@ -1051,11 +1061,10 @@ blst_radix_print(blmeta_t *scan, daddr_t blk, daddr_t radix, int tab)
mask = scan->bm_bitmap;
/* Examine the nonempty subtree associated with each bit set in mask */
do {
bit = mask & -mask;
digit = bitpos(bit);
digit = bitpos(mask);
blst_radix_print(&scan[1 + digit * skip], blk + digit * radix,
radix, tab);
} while ((mask ^= bit) != 0);
} while ((mask ^= bitrange(digit, 1)) != 0);
tab -= 4;
printf(