linux-kernel - Re: [PATCH v2 4/6] lib: Fix test_find_first_and_bit and test_find_next_and

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Message-ID: <ZtHpZzYE62qMvIFY@yury-ThinkPad>
Date: Fri, 30 Aug 2024 08:46:47 -0700
From: Yury Norov <yury.norov@...il.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] lib: Fix test_find_first_and_bit and
 test_find_next_and_bit benchmark

On Thu, Aug 29, 2024 at 09:59:24AM -0400, Mathieu Desnoyers wrote:
> Modify test_find_first_bit so it modifies a local copy of bitmap rather
> than modifying the input bitmap, which removes the requirement of
> placing it last in the tests.
> 
> Calls to test_find_first_and_bit and test_find_next_and_bit are placed
> after test_find_first_bit, which makes them use a bitmap entirely filled
> rather than the expected bitmap (random-filled or sparse).
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Yury Norov <yury.norov@...il.com>
> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  lib/find_bit_benchmark.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/find_bit_benchmark.c b/lib/find_bit_benchmark.c
> index d3fb09e6eff1..aee2ebb6b3cd 100644
> --- a/lib/find_bit_benchmark.c
> +++ b/lib/find_bit_benchmark.c
> @@ -30,18 +30,20 @@ static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
>  static DECLARE_BITMAP(bitmap2, BITMAP_LEN) __initdata;
>  
>  /*
> - * This is Schlemiel the Painter's algorithm. It should be called after
> - * all other tests for the same bitmap because it sets all bits of bitmap to 1.
> + * This is Schlemiel the Painter's algorithm.
>   */

Good to drop it, moreover, the comment is incorrect - we set all bits
to 0, not 1.

>  static int __init test_find_first_bit(void *bitmap, unsigned long len)
>  {
> +	static DECLARE_BITMAP(cp, BITMAP_LEN) __initdata;

This days we can allocate automatic variables, which is better than
statics:

   unsigned long *cp __free(bitmap) = bitmap_alloc(len, GFP_KERNEL);

If no objections, I can fix it inplace. The rest of the series looks
good. I'll add it in bitmap-for-next for testing shortly.

Thanks,
Yury

>  	unsigned long i, cnt;
>  	ktime_t time;
>  
> +	bitmap_copy(cp, bitmap, BITMAP_LEN);
> +
>  	time = ktime_get();
>  	for (cnt = i = 0; i < len; cnt++) {
> -		i = find_first_bit(bitmap, len);
> -		__clear_bit(i, bitmap);
> +		i = find_first_bit(cp, len);
> +		__clear_bit(i, cp);
>  	}
>  	time = ktime_get() - time;
>  	pr_err("find_first_bit:     %18llu ns, %6ld iterations\n", time, cnt);
> -- 
> 2.39.2