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Date:   Thu, 9 May 2019 02:30:24 +0000
From:   Qiang Zhao <qiang.zhao@....com>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Leo Li <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>,
        Christophe Leroy <christophe.leroy@....fr>,
        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

On 2019/5/1 17:29, Rasmus Villemoes <rasmus.villemoes@...vas.dk> wrote:

> -----Original Message-----
> From: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
> Sent: 2019年5月1日 17:29
> To: devicetree@...r.kernel.org; Qiang Zhao <qiang.zhao@....com>; Leo Li
> <leoyang.li@....com>
> Cc: linuxppc-dev@...ts.ozlabs.org; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org; Rob Herring <robh+dt@...nel.org>; Scott Wood
> <oss@...error.net>; Christophe Leroy <christophe.leroy@....fr>; Mark
> Rutland <mark.rutland@....com>; Rasmus Villemoes
> <Rasmus.Villemoes@...vas.se>
> Subject: [PATCH v2 2/6] soc/fsl/qe: qe.c: reduce static memory footprint
> by 1.7K
> 
> 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: Qiang Zhao <qiang.zhao@....com>

> ---
>  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);
> +       if (p)
> +               clear_bit(p - snums, snum_state);
>  }
>  EXPORT_SYMBOL(qe_put_snum);
> 
> --
> 2.20.1
Best Regards
Qiang Zhao

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