linux-kernel - Re: [PATCH v1] ath5k: fix WARNING opportunity for swap.

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Message-ID: <01fc3da3-dc67-8873-dd59-f77a7d067f33@quicinc.com>
Date:   Mon, 14 Aug 2023 15:28:18 -0700
From:   Jeff Johnson <quic_jjohnson@...cinc.com>
To:     Mahmoud Maatuq <mahmoudmatook.mm@...il.com>,
        <jirislaby@...nel.org>, <mickflemm@...il.com>, <mcgrof@...nel.org>,
        <kvalo@...nel.org>, <linux-wireless@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: Re: [PATCH v1] ath5k: fix WARNING opportunity for swap.

On 8/14/2023 1:02 PM, Mahmoud Maatuq wrote:
> coccinielle reported the following:
> ./drivers/net/wireless/ath/ath5k/phy.c:1573:25-26: WARNING opportunity for swap()

Suggest you add something like:

This revealed that ath5k_hw_get_median_noise_floor() had open-coded 
sort() functionality. Since ath5k_hw_get_median_noise_floor() only 
executes once every 10 seconds, any extra overhead due to sort() calling 
it's "compare" and "swap" functions can be ignored, so replace the 
existing logic with a call to sort().

and before your SOB add:
Suggested-by: Jiri Slaby <jirislaby@...nel.org>

> Signed-off-by: Mahmoud Maatuq <mahmoudmatook.mm@...il.com>
> ---
> changes in v1:
> - replace the entire double loop with sort()
>    as suggested by Jiri Slaby <jirislaby@...nel.org>
> ---
>   drivers/net/wireless/ath/ath5k/phy.c | 29 +++++++++++++---------------
>   1 file changed, 13 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/ath5k/phy.c b/drivers/net/wireless/ath/ath5k/phy.c
> index 5797ef9c73d7..7ee4e1616f45 100644
> --- a/drivers/net/wireless/ath/ath5k/phy.c
> +++ b/drivers/net/wireless/ath/ath5k/phy.c
> @@ -26,6 +26,7 @@
>   
>   #include <linux/delay.h>
>   #include <linux/slab.h>
> +#include <linux/sort.h>
>   #include <asm/unaligned.h>
>   
>   #include "ath5k.h"
> @@ -1554,6 +1555,11 @@ static void ath5k_hw_update_nfcal_hist(struct ath5k_hw *ah, s16 noise_floor)
>   	hist->nfval[hist->index] = noise_floor;
>   }
>   
> +static int cmps16(const void *a, const void *b)
> +{
> +	return *(s16 *)a - *(s16 *)b;
> +}
> +
>   /**
>    * ath5k_hw_get_median_noise_floor() - Get median NF from history buffer
>    * @ah: The &struct ath5k_hw
> @@ -1561,25 +1567,16 @@ static void ath5k_hw_update_nfcal_hist(struct ath5k_hw *ah, s16 noise_floor)
>   static s16
>   ath5k_hw_get_median_noise_floor(struct ath5k_hw *ah)
>   {
> -	s16 sort[ATH5K_NF_CAL_HIST_MAX];
> -	s16 tmp;
> -	int i, j;
> -
> -	memcpy(sort, ah->ah_nfcal_hist.nfval, sizeof(sort));
> -	for (i = 0; i < ATH5K_NF_CAL_HIST_MAX - 1; i++) {
> -		for (j = 1; j < ATH5K_NF_CAL_HIST_MAX - i; j++) {
> -			if (sort[j] > sort[j - 1]) {
> -				tmp = sort[j];
> -				sort[j] = sort[j - 1];
> -				sort[j - 1] = tmp;
> -			}
> -		}
> -	}
> +	s16 sorted_nfval[ATH5K_NF_CAL_HIST_MAX];
> +	int i;
> +
> +	memcpy(sorted_nfval, ah->ah_nfcal_hist.nfval, sizeof(sorted_nfval));
> +	sort(sorted_nfval, ATH5K_NF_CAL_HIST_MAX, sizeof(s16), cmps16, NULL);
>   	for (i = 0; i < ATH5K_NF_CAL_HIST_MAX; i++) {
>   		ATH5K_DBG(ah, ATH5K_DEBUG_CALIBRATE,
> -			"cal %d:%d\n", i, sort[i]);
> +			"cal %d:%d\n", i, sorted_nfval[i]);
>   	}
> -	return sort[(ATH5K_NF_CAL_HIST_MAX - 1) / 2];
> +	return sorted_nfval[(ATH5K_NF_CAL_HIST_MAX - 1) / 2];
>   }
>   
>   /**