linux-kernel - Re: [PATCH] riscv: defconfig: k210: Disable CONFIG

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Message-ID: <CH2PR04MB652268FD0FB44AA5DF36ACFBE7FA0@CH2PR04MB6522.namprd04.prod.outlook.com>
Date:   Wed, 25 Nov 2020 09:02:07 +0000
From:   Damien Le Moal <Damien.LeMoal@....com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: defconfig: k210: Disable CONFIG_VT

On 2020/11/25 17:51, Geert Uytterhoeven wrote:
> Hi Damien,
> 
> On Wed, Nov 25, 2020 at 7:14 AM Damien Le Moal <Damien.LeMoal@....com> wrote:
>> On 2020/11/25 3:57, Geert Uytterhoeven wrote:
>>> There is no need to enable Virtual Terminal support in the Canaan
>>> Kendryte K210 defconfigs, as no terminal devices are supported and
>>> enabled.  Hence disable CONFIG_VT, and remove the no longer needed
>>> override for CONFIG_VGA_CONSOLE.
>>>
>>> This reduces kernel size by ca. 65 KiB.
>>
>> Indeed, nice saving. Just tested, and all is good.
> 
> I used my old script[1] to check the impact of disabling config options.
> 
> I don't see any other low-hanging fruits:
> 
> Disabling CONFIG_BLOCK saves 492890 bytes
> Disabling CONFIG_EXT4_FS saves 322528 bytes
> Disabling CONFIG_PRINTK saves 214612 bytes
> Disabling CONFIG_SMP saves 214486 bytes
> Disabling CONFIG_FRAME_POINTER saves 166368 bytes
> Disabling CONFIG_TTY saves 156618 bytes
> Disabling CONFIG_PROC_FS saves 110274 bytes
> Disabling CONFIG_MMC saves 87656 bytes
> Disabling CONFIG_VT saves 70350 bytes
> Disabling CONFIG_SYSFS saves 62298 bytes
> Disabling CONFIG_BUG saves 50882 bytes
> Disabling CONFIG_SPI saves 34420 bytes
> Disabling CONFIG_SOC_CANAAN saves 34286 bytes
> Disabling CONFIG_I2C saves 34086 bytes
> Disabling CONFIG_PROC_SYSCTL saves 23890 bytes
> Disabling CONFIG_POSIX_TIMERS saves 18388 bytes
> Disabling CONFIG_I2C_DESIGNWARE_PLATFORM saves 17530 bytes
> Disabling CONFIG_MMC_BLOCK saves 17200 bytes
> Disabling CONFIG_UNIX98_PTYS saves 16360 bytes
> Disabling CONFIG_MULTIUSER saves 16148 bytes
> Disabling CONFIG_NEW_LEDS saves 15964 bytes
> Disabling CONFIG_SPI_DESIGNWARE saves 15434 bytes
> Disabling CONFIG_GPIO_CDEV saves 15352 bytes
> Disabling CONFIG_MMC_SPI saves 14754 bytes
> Disabling CONFIG_SOC_CANAAN_K210_DTB_BUILTIN saves 13864 bytes
> 
> (Yes, I have ext4 enabled ;-)
> 
> I haven't done enough riscv kernel development yet to assess if I need
> CONFIG_FRAME_POINTER or not.

Disabling it significantly reduced code size for me. Since the series is more
stable now, it is not really needed, so I disabled it in the defconfig.

I was just fiddling with CONFIG_UNIX98_PTYS. Disabling it is OK with the simple
busybox userspace (no telnet/xterm like app running). But it saves only about
1KB with my toolchain (gcc 9.3). So I left that one enabled. I am surprised that
you see 16K size impact... How big is your image ?

For me, it is 1.768 MB right now for the sdcard defconfig, with CONFIG_VT
disabled and ext2 enabled.

Disabling the block layer, ext2 and mmc driver, the size goes down to 1.511 MB
without any intramfs cpio file embedded.

> 
> [1] https://github.com/geertu/linux-scripts/blob/master/linux-analyze-marginal-sizes

Thanks ! I will try to run this on my end.

> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 


-- 
Damien Le Moal
Western Digital Research