Re: [PATCH v7 1/2] lib: bitmap: add tests for bitmap_find_next_zero_area_off()

["Michał Nazarewicz" <mina86@mina86.com>]

On Mon, Jun 22 2026, Yi Sun wrote:
> Add functional and performance tests
> for bitmap_find_next_zero_area_off().
>
> performance tests partial output:
> Start testing find_bit() with random-filled bitmap
> [    0.310073] bitmap_find_next_zero_area_off: 852731 ns,   1154 iterations
> [    0.311435] find_next_bit:                 1356654 ns, 163975 iterations
> Start testing find_bit() with sparse bitmap
> [    0.316267] bitmap_find_next_zero_area_off:4426808 ns, 322479 iterations
> [    0.316292] find_next_bit:                   15154 ns,    656 iterations
>
> Signed-off-by: Yi Sun <yi.sun@unisoc.com>

Acked-by: Michał Nazarewicz <mina86@mina86.com>

> ---
>  lib/find_bit_benchmark.c | 17 +++++++++++++++++
>  lib/test_bitmap.c        | 38 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+)
>
> diff --git a/lib/find_bit_benchmark.c b/lib/find_bit_benchmark.c
> index 00d9dc61cd46..05305e655f99 100644
> --- a/lib/find_bit_benchmark.c
> +++ b/lib/find_bit_benchmark.c
> @@ -149,6 +149,21 @@ static int __init test_find_next_and_bit(const void *bitmap,
>  	return 0;
>  }
>  
> +static int __init
> +test_bitmap_find_next_zero_area_off(unsigned long *bitmap, unsigned long len)
> +{
> +	unsigned long i, cnt;
> +	ktime_t time;
> +
> +	time = ktime_get();
> +	for (cnt = i = 0; i < BITMAP_LEN; cnt++)
> +		i = bitmap_find_next_zero_area_off(bitmap, BITMAP_LEN, i, 8, 0, 0) + 1;
> +	time = ktime_get() - time;
> +	pr_err("bitmap_find_next_zero_area_off:%7llu ns, %6ld iterations\n", time, cnt);
> +
> +	return 0;
> +}
> +
>  static int __init find_bit_test(void)
>  {
>  	unsigned long nbits = BITMAP_LEN / SPARSE;
> @@ -158,6 +173,7 @@ static int __init find_bit_test(void)
>  	get_random_bytes(bitmap, sizeof(bitmap));
>  	get_random_bytes(bitmap2, sizeof(bitmap2));
>  
> +	test_bitmap_find_next_zero_area_off(bitmap, BITMAP_LEN);
>  	test_find_next_bit(bitmap, BITMAP_LEN);
>  	test_find_next_zero_bit(bitmap, BITMAP_LEN);
>  	test_find_last_bit(bitmap, BITMAP_LEN);
> @@ -181,6 +197,7 @@ static int __init find_bit_test(void)
>  		__set_bit(get_random_u32_below(BITMAP_LEN), bitmap2);
>  	}
>  
> +	test_bitmap_find_next_zero_area_off(bitmap, BITMAP_LEN);
>  	test_find_next_bit(bitmap, BITMAP_LEN);
>  	test_find_next_zero_bit(bitmap, BITMAP_LEN);
>  	test_find_last_bit(bitmap, BITMAP_LEN);
> diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
> index 69813c10e6c0..8665df77c960 100644
> --- a/lib/test_bitmap.c
> +++ b/lib/test_bitmap.c
> @@ -234,6 +234,43 @@ static void __init test_find_nth_bit(void)
>  	}
>  }
>  
> +static void __init
> +test_bitmap_find_next_zero_area_off(void)
> +{
> +	DECLARE_BITMAP(bmap, 192);
> +
> +	bitmap_set(bmap, 0, 192);
> +
> +	bitmap_clear(bmap, 0, 8);
> +	__clear_bit(50, bmap);
> +	bitmap_clear(bmap, 60, 18);
> +	__set_bit(69, bmap);
> +	__clear_bit(80, bmap);
> +	bitmap_clear(bmap, 100, 10);
> +	__clear_bit(120, bmap);
> +	bitmap_clear(bmap, 145, 8);
> +	bitmap_clear(bmap, 160, 32);
> +
> +	expect_eq_uint(0,
> +		bitmap_find_next_zero_area_off(bmap, 192, 0, 8, 0, 0));
> +	expect_eq_uint(0,
> +		bitmap_find_next_zero_area_off(bmap, 192, 0, 8, 3, 0));
> +	expect_eq_uint(163,
> +		bitmap_find_next_zero_area_off(bmap, 192, 0, 8, 3, 1));
> +	expect_eq_uint(60,
> +		bitmap_find_next_zero_area_off(bmap, 192, 1, 8, 0, 0));
> +	expect_eq_uint(160,
> +		bitmap_find_next_zero_area_off(bmap, 192, 1, 8, 7, 0));
> +	expect_eq_uint(60,
> +		bitmap_find_next_zero_area_off(bmap, 192, 1, 8, 7, 4));
> +	expect_eq_uint(100,
> +		bitmap_find_next_zero_area_off(bmap, 192, 0, 10, 0, 0));
> +	expect_eq_uint(160,
> +		bitmap_find_next_zero_area_off(bmap, 192, 0, 32, 0, 0));
> +	expect_eq_uint(1,
> +		!!(bitmap_find_next_zero_area_off(bmap, 192, 0, 33, 0, 0) >= 192));

In C `x >= y` yields 0 or 1.  There’s no need for `!!`.

About `>` vs `>=`, the original code returns `> 192` (because it returns
`end` when it exceeds `size`).  The new code returns `192` (because it
returns `size` if loop fails to find an area).  If that’s the case, this
patch, PATCH 1/2, should have `>` and PATCH 2/2 should change it to
`expect_eq_uint(192, …)` to reflect change in the API.
 
> +}
> +
>  static void __init test_fill_set(void)
>  {
>  	DECLARE_BITMAP(bmap, 1024);
> @@ -1559,6 +1596,7 @@ static void __init selftest(void)
>  	test_for_each_clear_bitrange_from();
>  	test_for_each_set_clump8();
>  	test_for_each_set_bit_wrap();
> +	test_bitmap_find_next_zero_area_off();
>  }
>  
>  KSTM_MODULE_LOADERS(test_bitmap);

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴィツ
«If at first you don’t succeed, give up skydiving»