linux-kernel - Re: [PATCH v4 1/1] riscv: __asm_copy_to-from_user: Optimize unaligned memory access and pipeline stall

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Date:   Mon, 19 Jul 2021 23:49:53 +0900
From:   Akira Tsukamoto <akira.tsukamoto@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Palmer Dabbelt <palmer@...belt.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Qiu Wenbo <qiuwenbo@...inos.com.cn>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] riscv: __asm_copy_to-from_user: Optimize unaligned
 memory access and pipeline stall


On 7/19/2021 11:24 PM, Guenter Roeck wrote:
> On 7/19/21 7:00 AM, Akira Tsukamoto wrote:
>>
>> On 7/19/2021 10:51 PM, Guenter Roeck wrote:
>>> Hi,
>>>
>>> On 7/19/21 5:53 AM, Akira Tsukamoto wrote:
>>>>
>>>> This patch will reduce cpu usage dramatically in kernel space especially
>>>> for application which use sys-call with large buffer size, such as
>>>> network applications. The main reason behind this is that every
>>>> unaligned memory access will raise exceptions and switch between s-mode
>>>> and m-mode causing large overhead.
>>>>
>>>
>>> I had to revert the original patch from the mainline kernel prior to applying
>>> this patch. Obviously that means that there may be other changes affecting the
>>> outcome.
>>>
>>> riscv64 images work, but riscv32 images still fail with this patch applied.
>>> The error is a bit different than before, though.
>>>
>>> ...
>>> [   11.899979] Run /sbin/init as init process
>>> [   12.152666] random: fast init done
>>> moun: applet not found
>>> "�����V�t: applet not found
>>> /bi�����V�F-: applet not found
>>> moun: applet not found
>>> swaon: applet not found
>>> hostname-F: applet not found
>>>
>>> After this, the image hangs.
>>>
>>> For comparison, the mainline kernel (v5.14-rc2) fails as follows.
>>>
>>> [   10.788105] Run /sbin/init as init process
>>> Starting syslogd: OK
>>> Starting klogd: OK
>>> /etc/init.d/S02sysctl: line 68: syntax error: EOF in backquote substitution
>>> /etc/init.d/S20urandom: line 1: syntax error: unterminated quoted string
>>> Starting network: /bin/sh: syntax error: unterminated quoted string
>>> sed: unmatched '/'
>>> /bin/sh: syntax error: unterminated quoted string
>>> FAIL
>>> /etc/init.d/S55runtest: line 48: syntax error: EOF in backquote substitution
>>>
>>> I'll be happy to provide information on how to reproduce the problem
>>> if needed. Please let me know.
>>
>> Yes, I do would like to know the procedure of build instruction of your rv32 image.
>> Then I would reproduce the error and look into how to fix it.
>>
> Please have a look at http://server.roeck-us.net/qemu/riscv32/
> and let me know if you need anything else.

Thanks for the link. I will work on it tomorrow in my time.
Building the kernel with defconfig looks much quicker than the config.
I will try it from defconfig and then config.

Also I would like to use the same rv32 toolchain. Are you using prebuilt
riscv32-linux-gcc? Should not make differences but just in case.

Is there a public reference for the way of building your qemu and opensbi?
Not sure which version of qemu with which rv32 to build them, rv32i, rv32imad or else.

I really appreciate your help.

Akira