diff options
| author | Alexander Lobakin <aleksander.lobakin@intel.com> | 2024-03-27 16:23:49 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-09-04 13:12:59 +0200 |
| commit | 188729977a0cfac6e04a59bf75f85ccd19ad4b4d (patch) | |
| tree | 89126c72002af492e3ef233127d225e3661a1053 /include | |
| parent | 90a6b797e95d0f4bef30fbab423759f4e9999506 (diff) | |
bitmap: introduce generic optimized bitmap_size()
commit a37fbe666c016fd89e4460d0ebfcea05baba46dc upstream.
The number of times yet another open coded
`BITS_TO_LONGS(nbits) * sizeof(long)` can be spotted is huge.
Some generic helper is long overdue.
Add one, bitmap_size(), but with one detail.
BITS_TO_LONGS() uses DIV_ROUND_UP(). The latter works well when both
divident and divisor are compile-time constants or when the divisor
is not a pow-of-2. When it is however, the compilers sometimes tend
to generate suboptimal code (GCC 13):
48 83 c0 3f add $0x3f,%rax
48 c1 e8 06 shr $0x6,%rax
48 8d 14 c5 00 00 00 00 lea 0x0(,%rax,8),%rdx
%BITS_PER_LONG is always a pow-2 (either 32 or 64), but GCC still does
full division of `nbits + 63` by it and then multiplication by 8.
Instead of BITS_TO_LONGS(), use ALIGN() and then divide by 8. GCC:
8d 50 3f lea 0x3f(%rax),%edx
c1 ea 03 shr $0x3,%edx
81 e2 f8 ff ff 1f and $0x1ffffff8,%edx
Now it shifts `nbits + 63` by 3 positions (IOW performs fast division
by 8) and then masks bits[2:0]. bloat-o-meter:
add/remove: 0/0 grow/shrink: 20/133 up/down: 156/-773 (-617)
Clang does it better and generates the same code before/after starting
from -O1, except that with the ALIGN() approach it uses %edx and thus
still saves some bytes:
add/remove: 0/0 grow/shrink: 9/133 up/down: 18/-538 (-520)
Note that we can't expand DIV_ROUND_UP() by adding a check and using
this approach there, as it's used in array declarations where
expressions are not allowed.
Add this helper to tools/ as well.
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/bitmap.h | 8 | ||||
| -rw-r--r-- | include/linux/cpumask.h | 2 |
2 files changed, 6 insertions, 4 deletions
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index b71a033c781e..6bcc7e72bc5a 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -212,12 +212,14 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf, #define small_const_nbits(nbits) \ (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0) +#define bitmap_size(nbits) (ALIGN(nbits, BITS_PER_LONG) / BITS_PER_BYTE) + static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) { if (small_const_nbits(nbits)) *dst = 0UL; else { - unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); + unsigned int len = bitmap_size(nbits); memset(dst, 0, len); } } @@ -227,7 +229,7 @@ static inline void bitmap_fill(unsigned long *dst, unsigned int nbits) if (small_const_nbits(nbits)) *dst = ~0UL; else { - unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); + unsigned int len = bitmap_size(nbits); memset(dst, 0xff, len); } } @@ -238,7 +240,7 @@ static inline void bitmap_copy(unsigned long *dst, const unsigned long *src, if (small_const_nbits(nbits)) *dst = *src; else { - unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); + unsigned int len = bitmap_size(nbits); memcpy(dst, src, len); } } diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index 147bdec42215..e4467240eb86 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -656,7 +656,7 @@ static inline int cpulist_parse(const char *buf, struct cpumask *dstp) */ static inline unsigned int cpumask_size(void) { - return BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long); + return bitmap_size(nr_cpumask_bits); } /* |