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Commit 18872997 authored by Alexander Lobakin's avatar Alexander Lobakin Committed by Greg Kroah-Hartman
Browse files

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: default avatarPrzemek Kitszel <przemyslaw.kitszel@intel.com>
Acked-by: default avatarYury Norov <yury.norov@gmail.com>
Signed-off-by: default avatarAlexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 90a6b797

drivers/s390/cio/idset.c

+1 −1
Original line number Diff line number Diff line
@@ -18,7 +18,7 @@ struct idset { 


static inline unsigned long bitmap_size(int num_ssid, int num_id)

{

	return BITS_TO_LONGS(num_ssid * num_id) * sizeof(unsigned long);

	return bitmap_size(size_mul(num_ssid, num_id));

}



static struct idset *idset_new(int num_ssid, int num_id)

include/linux/bitmap.h

+5 −3
Original line number Diff line number Diff line
@@ -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);

	}

}

include/linux/cpumask.h

+1 −1
Original line number Diff line number Diff line
@@ -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);

}



/*

tools/include/linux/bitmap.h

+4 −3
Original line number Diff line number Diff line
@@ -27,13 +27,14 @@ int __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, 
#define small_const_nbits(nbits) \

	(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)



#define bitmap_size(nbits)	(ALIGN(nbits, BITS_PER_LONG) / BITS_PER_BYTE)



static inline void bitmap_zero(unsigned long *dst, int nbits)

{

	if (small_const_nbits(nbits))

		*dst = 0UL;

	else {

		int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);

		memset(dst, 0, len);

		memset(dst, 0, bitmap_size(nbits));

	}

}
@@ -119,7 +120,7 @@ static inline int test_and_clear_bit(int nr, unsigned long *addr) 
 */

static inline unsigned long *bitmap_alloc(int nbits)

{

	return calloc(1, BITS_TO_LONGS(nbits) * sizeof(unsigned long));

	return calloc(1, bitmap_size(nbits));

}



/*