[PATCH v3 0/2] Improve the performance of bitmap_find_next_zero_area_off()

[Yi Sun <yi.sun@unisoc.com>]

Based on Michał Nazarewicz's suggestion,
code optimization was performed on PATCH v1.

Replacing find_next_bit() with find_last_bit_from()
can improve performance by an average of 50%.
The test results can be viewed in PATCH v1.


This section compares the performance of PATCH v2 and PATCH v3.
Test results show that PATCH v3 performs slightly better
than PATCH v2 in most cases.
When the number of 'goto again' loops is large,
PATCH v3's advantage becomes more apparent.


Test result:
	cnt	again_cnt	v2_time(ns)	v3_time(ns)	time_ratio
test1	8	9		230		242		-5.2%
test2	8	1		75		76		around 0%

test1	8	329		4452		4242		4.7%
test2	8	1		46		47		around 0%

test1	32	10414		139015		132700		4.5%
test2	32	1		47		47		around 0%

test1	128	2570		34163		32711		4.3%
test2	128	1		46		46		around 0%

test1	1024	321		4293		4098		4.5%
test2	1024	6		126		122		3.2%

test1	4096	81		1087		1046		3.8%
test2	4096	92		1656		1570		5.2%

Test result explanation:
@test1: The bitmap is filled with random numbers,
so the bitmap is very messy.
@test2: Sparse bitmap.

@cnt: The expected number of consecutive clear bits.

@again_cnt: The number of 'goto again'.

@v2_time(ns): The total time consumed by
bitmap_find_next_zero_area_off() when
using PATCH v2.
@v3_time(ns): The total time consumed by
bitmap_find_next_zero_area_off() when
using PATCH v3.
@time_ratio = (v2_time - v3_time) / v2_time.

---
v2: https://lore.kernel.org/all/20260514035644.4118050-1-yi.sun@unisoc.com
- Do not introduce find_last_bit_from().

v1: https://lore.kernel.org/all/20260512040659.2992142-1-yi.sun@unisoc.com


Yi Sun (2):
  lib: bitmap: add find_last_bit_from() and _find_last_bit_from()
  lib: bitmap: reduce the number of goto again in
    bitmap_find_next_zero_area_off()

 include/linux/find.h | 33 +++++++++++++++++++++++++++++++++
 lib/bitmap.c         |  2 +-
 lib/find_bit.c       | 22 ++++++++++++++++++++++
 3 files changed, 56 insertions(+), 1 deletion(-)

-- 
2.34.1