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lib/find_bit: add find_next{,_and}_bit_wrap

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The helper is better optimized for the worst case: in case of empty
cpumask, current code traverses 2 * size:

  next = cpumask_next_and(prev, src1p, src2p);
  if (next >= nr_cpu_ids)
  	next = cpumask_first_and(src1p, src2p);

At bitmap level we can stop earlier after checking 'size + offset' bits.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
This commit is contained in:
Yury Norov 2022-09-19 14:05:56 -07:00
parent 33e67710be
commit 6cc18331a9
2 changed files with 49 additions and 9 deletions
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46
include/linux/find.h
View File

@ -290,6 +290,52 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
}
#endif
/**
* find_next_and_bit_wrap - find the next set bit in both memory regions
* @addr1: The first address to base the search on
* @addr2: The second address to base the search on
* @size: The bitmap size in bits
* @offset: The bitnumber to start searching at
*
* Returns the bit number for the next set bit, or first set bit up to @offset
* If no bits are set, returns @size.
*/
static inline
unsigned long find_next_and_bit_wrap(const unsigned long *addr1,
const unsigned long *addr2,
unsigned long size, unsigned long offset)
{
unsigned long bit = find_next_and_bit(addr1, addr2, size, offset);
if (bit < size)
return bit;
bit = find_first_and_bit(addr1, addr2, offset);
return bit < offset ? bit : size;
}
/**
* find_next_bit_wrap - find the next set bit in both memory regions
* @addr: The first address to base the search on
* @size: The bitmap size in bits
* @offset: The bitnumber to start searching at
*
* Returns the bit number for the next set bit, or first set bit up to @offset
* If no bits are set, returns @size.
*/
static inline
unsigned long find_next_bit_wrap(const unsigned long *addr,
unsigned long size, unsigned long offset)
{
unsigned long bit = find_next_bit(addr, size, offset);
if (bit < size)
return bit;
bit = find_first_bit(addr, offset);
return bit < offset ? bit : size;
}
/**
* find_next_clump8 - find next 8-bit clump with set bits in a memory region
* @clump: location to store copy of found clump

12
lib/cpumask.c
View File

@ -166,10 +166,8 @@ unsigned int cpumask_any_and_distribute(const struct cpumask *src1p,
/* NOTE: our first selection will skip 0. */
prev = __this_cpu_read(distribute_cpu_mask_prev);
next = cpumask_next_and(prev, src1p, src2p);
if (next >= nr_cpu_ids)
next = cpumask_first_and(src1p, src2p);
next = find_next_and_bit_wrap(cpumask_bits(src1p), cpumask_bits(src2p),
nr_cpumask_bits, prev + 1);
if (next < nr_cpu_ids)
__this_cpu_write(distribute_cpu_mask_prev, next);
@ -183,11 +181,7 @@ unsigned int cpumask_any_distribute(const struct cpumask *srcp)
/* NOTE: our first selection will skip 0. */
prev = __this_cpu_read(distribute_cpu_mask_prev);
next = cpumask_next(prev, srcp);
if (next >= nr_cpu_ids)
next = cpumask_first(srcp);
next = find_next_bit_wrap(cpumask_bits(srcp), nr_cpumask_bits, prev + 1);
if (next < nr_cpu_ids)
__this_cpu_write(distribute_cpu_mask_prev, next);