Author: dougm Date: Sat May 11 09:09:10 2019 New Revision: 347484 URL: https://svnweb.freebsd.org/changeset/base/347484
Log: When bitpos can't be implemented with an inline ffs* instruction, 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 Modified: head/sys/kern/subr_blist.c Modified: head/sys/kern/subr_blist.c ============================================================================== --- head/sys/kern/subr_blist.c Sat May 11 04:18:06 2019 (r347483) +++ head/sys/kern/subr_blist.c Sat May 11 09:09:10 2019 (r347484) @@ -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 -bitpos(u_daddr_t mask) +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) +{ + 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_ * 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_ 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 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( _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
