linux-kernel - Re: [PATCH v2 2/6] soc/fsl/qe: qe.c: reduce static memory footprint by 1.7K

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Message-ID: <cae22a68-40f3-5993-22a0-222134e76def@c-s.fr>
Date:   Thu, 2 May 2019 06:51:37 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Qiang Zhao <qiang.zhao@....com>, Li Yang <leoyang.li@....com>
Cc:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Scott Wood <oss@...error.net>,
        Mark Rutland <mark.rutland@....com>,
        Rasmus Villemoes <Rasmus.Villemoes@...vas.se>
Subject: Re: [PATCH v2 2/6] soc/fsl/qe: qe.c: reduce static memory footprint
 by 1.7K



Le 01/05/2019 à 11:29, 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>

Reviewed-by: Christophe Leroy <christophe.leroy@....fr>

Trivial comment below

> ---
>   drivers/soc/fsl/qe/qe.c | 43 ++++++++++++-----------------------------
>   1 file changed, 12 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/soc/fsl/qe/qe.c b/drivers/soc/fsl/qe/qe.c
> index 855373deb746..303aa29cb27d 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;
> @@ -315,10 +305,8 @@ 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;
> -	}
> +	bitmap_zero(snum_state, QE_NUM_OF_SNUM);
> +	memcpy(snums, snum_init, qe_num_of_snum);
>   }
>   
>   int qe_get_snum(void)
> @@ -328,12 +316,10 @@ 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);
>   
> @@ -343,14 +329,9 @@ EXPORT_SYMBOL(qe_get_snum);
>   
>   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;
> -			break;
> -		}
> -	}
> +	const u8 *p = memchr(snums, snum, qe_num_of_snum);

A blank line is expected here.

Christophe

> +	if (p)
> +		clear_bit(p - snums, snum_state);
>   }
>   EXPORT_SYMBOL(qe_put_snum);
>   
>