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lib: add find_first_and_bit()

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Currently find_first_and_bit() is an alias to find_next_and_bit(). However,
it is widely used in cpumask, so it worth to optimize it. This patch adds
its own implementation for find_first_and_bit().

On x86_64 find_bit_benchmark says:

Before (#define find_first_and_bit(...) find_next_and_bit(..., 0):
Start testing find_bit() with random-filled bitmap
[  140.291468] find_first_and_bit:           46890919 ns,  32671 iterations
Start testing find_bit() with sparse bitmap
[  140.295028] find_first_and_bit:               7103 ns,      1 iterations

After:
Start testing find_bit() with random-filled bitmap
[  162.574907] find_first_and_bit:           25045813 ns,  32846 iterations
Start testing find_bit() with sparse bitmap
[  162.578458] find_first_and_bit:               4900 ns,      1 iterations

(Thanks to Alexey Klimov for thorough testing.)

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Alexey Klimov <aklimov@redhat.com>
This commit is contained in:
Yury Norov
2021-08-14 14:17:01 -07:00
parent c126a53c27
commit f68edc9297
3 changed files with 69 additions and 0 deletions
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21
lib/find_bit.c
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@@ -89,6 +89,27 @@ unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
EXPORT_SYMBOL(_find_first_bit);
#endif
#ifndef find_first_and_bit
/*
* Find the first set bit in two memory regions.
*/
unsigned long _find_first_and_bit(const unsigned long *addr1,
const unsigned long *addr2,
unsigned long size)
{
unsigned long idx, val;
for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
val = addr1[idx] & addr2[idx];
if (val)
return min(idx * BITS_PER_LONG + __ffs(val), size);
}
return size;
}
EXPORT_SYMBOL(_find_first_and_bit);
#endif
#ifndef find_first_zero_bit
/*
* Find the first cleared bit in a memory region.