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

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Date:   Wed, 25 Nov 2020 11:00:08 +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 18:26, Geert Uytterhoeven wrote:
> Hi Damien,
> 
> On Wed, Nov 25, 2020 at 10:02 AM Damien Le Moal <Damien.LeMoal@....com> wrote:
>> On 2020/11/25 17:51, Geert Uytterhoeven wrote:
>>> 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 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.
> 
> It might depend on how you measure.  "size" says 15 KiB impact for UNIX98
> ptys, while bloat-o-meter reported less than 7 (my script uses "size").

I look at the size of the arch/riscv/boot/loader.bin file since that is what
gets loaded in RAM and booted. It is significantly smaller than vmlinux file
size. E.g. for the sd card defconfig, I have:

vmlinux: 2369920 B
loader.bin: 1751250 B

> I'm at 1.88 MiB, with ext4 and without frame pointers.
> I also got rid of the EFI partition support, and a few I/O schedulers:
> 
> +CONFIG_PARTITION_ADVANCED=y
> +# CONFIG_EFI_PARTITION is not set
> +# CONFIG_MQ_IOSCHED_DEADLINE is not set
> +# CONFIG_MQ_IOSCHED_KYBER is not set

I have all of these disabled. The schedulers are forced disabled in the sdcard
defconfig.

I also noticed that it hugely depend on the compiler. Using the buildroot
generated rv64 gcc 10, the kernel image goes up to almost 2 MB. So for the
kernel, I keep using the bootlin precompiled gcc 9.3:

https://toolchains.bootlin.com/

Just noticed that they now have a 10.2 version available. Will try it out.

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


-- 
Damien Le Moal
Western Digital Research