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

[Yury Norov <ynorov@nvidia.com>]

You submitted v2 and v3 within the same day. This is not how things
are working. So, should I ignore v2 now? Please allow your reviewers
at least a few days before submitting any follow ups.

On Thu, May 14, 2026 at 05:06:05PM +0800, Yi Sun wrote:
> 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.

In v1 discussion, I asked you to turn your testing code into the
addition to lib/find_bit_benchmark. Any reason to ignore that?

Whatever you end up, it should not look how it looks now. I want
to be able to compile the find_bit_benchmark, then run it before
applying your series, and after that, and just compare 2 numbers
for dense and 2 numbers for sparse bitmaps.

Refer to e3783c805db29c8 as an example of how the tests look.

> ---
> 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