linux-kernel - Re: [PATCH 2/5] soc/fsl/qe: qe.c: reduce static memory footprint by 1.7K

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Message-ID: <51b00425-58a7-089a-67a9-61cd315d5097@c-s.fr>
Date:   Tue, 30 Apr 2019 19:12:15 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Qiang Zhao <qiang.zhao@....com>, Li Yang <leoyang.li@....com>
Cc:     Valentin Longchamp <valentin.longchamp@...mile.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Scott Wood <oss@...error.net>,
        Rasmus Villemoes <Rasmus.Villemoes@...vas.se>,
        Rob Herring <robh+dt@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/5] soc/fsl/qe: qe.c: reduce static memory footprint by
 1.7K



Le 30/04/2019 à 15:36, Rasmus Villemoes a écrit :
> The current array of struct qe_snum use 256*4 bytes for just keeping
> track of the free/used state of each index, and the struct layout
> means there's another 768 bytes of padding. If we just unzip that
> structure, the array of snum values just use 256 bytes, while the
> free/inuse state can be tracked in a 32 byte bitmap.
> 
> So this reduces the .data footprint by 1760 bytes. It also serves as
> preparation for introducing another DT binding for specifying the snum
> values.
> 
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
> ---
>   drivers/soc/fsl/qe/qe.c | 37 ++++++++++++-------------------------
>   1 file changed, 12 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/soc/fsl/qe/qe.c b/drivers/soc/fsl/qe/qe.c
> index 855373deb746..d0393f83145c 100644
> --- a/drivers/soc/fsl/qe/qe.c
> +++ b/drivers/soc/fsl/qe/qe.c
> @@ -14,6 +14,7 @@
>    * Free Software Foundation;  either version 2 of the  License, or (at your
>    * option) any later version.
>    */
> +#include <linux/bitmap.h>
>   #include <linux/errno.h>
>   #include <linux/sched.h>
>   #include <linux/kernel.h>
> @@ -43,25 +44,14 @@ static DEFINE_SPINLOCK(qe_lock);
>   DEFINE_SPINLOCK(cmxgcr_lock);
>   EXPORT_SYMBOL(cmxgcr_lock);
>   
> -/* QE snum state */
> -enum qe_snum_state {
> -	QE_SNUM_STATE_USED,
> -	QE_SNUM_STATE_FREE
> -};
> -
> -/* QE snum */
> -struct qe_snum {
> -	u8 num;
> -	enum qe_snum_state state;
> -};
> -
>   /* We allocate this here because it is used almost exclusively for
>    * the communication processor devices.
>    */
>   struct qe_immap __iomem *qe_immr;
>   EXPORT_SYMBOL(qe_immr);
>   
> -static struct qe_snum snums[QE_NUM_OF_SNUM];	/* Dynamically allocated SNUMs */
> +static u8 snums[QE_NUM_OF_SNUM];	/* Dynamically allocated SNUMs */
> +static DECLARE_BITMAP(snum_state, QE_NUM_OF_SNUM);
>   static unsigned int qe_num_of_snum;
>   
>   static phys_addr_t qebase = -1;
> @@ -308,6 +298,7 @@ static void qe_snums_init(void)
>   	};
>   	const u8 *snum_init;
>   
> +	bitmap_zero(snum_state, QE_NUM_OF_SNUM);

Doesn't make much importance, but wouldn't it be more logical to add 
this line where the setting of .state = QE_SNUM_STATE_FREE was done 
previously, ie around the for() loop below ?

>   	qe_num_of_snum = qe_get_num_of_snums();
>   
>   	if (qe_num_of_snum == 76)
> @@ -315,10 +306,8 @@ static void qe_snums_init(void)
>   	else
>   		snum_init = snum_init_46;
>   
> -	for (i = 0; i < qe_num_of_snum; i++) {
> -		snums[i].num = snum_init[i];
> -		snums[i].state = QE_SNUM_STATE_FREE;
> -	}
> +	for (i = 0; i < qe_num_of_snum; i++)
> +		snums[i] = snum_init[i];

Could use memcpy() instead ?

>   }
>   
>   int qe_get_snum(void)
> @@ -328,12 +317,10 @@ int qe_get_snum(void)
>   	int i;
>   
>   	spin_lock_irqsave(&qe_lock, flags);
> -	for (i = 0; i < qe_num_of_snum; i++) {
> -		if (snums[i].state == QE_SNUM_STATE_FREE) {
> -			snums[i].state = QE_SNUM_STATE_USED;
> -			snum = snums[i].num;
> -			break;
> -		}
> +	i = find_first_zero_bit(snum_state, qe_num_of_snum);
> +	if (i < qe_num_of_snum) {
> +		set_bit(i, snum_state);
> +		snum = snums[i];
>   	}
>   	spin_unlock_irqrestore(&qe_lock, flags);
>   
> @@ -346,8 +333,8 @@ void qe_put_snum(u8 snum)
>   	int i;
>   
>   	for (i = 0; i < qe_num_of_snum; i++) {
> -		if (snums[i].num == snum) {
> -			snums[i].state = QE_SNUM_STATE_FREE;
> +		if (snums[i] == snum) {
> +			clear_bit(i, snum_state);
>   			break;
>   		}
>   	}

Can we replace this loop by memchr() ?

Christophe