linux-kernel - Re: [PATCH] LoongArch: Add unaligned access support

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Message-Id: <995e1d32-7818-4a44-9911-705dd1c62929@app.fastmail.com>
Date:   Mon, 17 Oct 2022 10:22:00 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "WANG Xuerui" <kernel@...0n.name>,
        "Huacai Chen" <chenhuacai@...nel.org>
Cc:     "Huacai Chen" <chenhuacai@...ngson.cn>, loongarch@...ts.linux.dev,
        "Xuefeng Li" <lixuefeng@...ngson.cn>,
        "Tiezhu Yang" <yangtiezhu@...ngson.cn>, guoren <guoren@...nel.org>,
        "Jiaxun Yang" <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Add unaligned access support

On Mon, Oct 17, 2022, at 10:05 AM, WANG Xuerui wrote:
> On 2022/10/17 15:38, Arnd Bergmann wrote:
>> On Mon, Oct 17, 2022, at 9:31 AM, Huacai Chen wrote:
>>>>> +/* sysctl hooks */
>>>>> +int unaligned_enabled __read_mostly = 1;     /* Enabled by default */
>>>>> +int no_unaligned_warning __read_mostly = 1;  /* Only 1 warning by default */
>>>>
>>>> The comment says 'sysctl', the implementation has a debugfs interface.
>>> Originally "enabled", "warning" and "counters" are all debugfs
>>> interfaces, then you told me to use sysctl. Now in this version
>>> "enabled" and "warning" are converted to sysctl, but there are no
>>> existing "counters" sysctl.
>> 
>> I don't see the sysctl interface in the patch, what am I missing?
>
> FYI they are chosen by the Kconfig options and live in kernel/sysctl.c. 

Got it, that's what I was looking for, I had completely forgotten
about how we got here.

> And I believe the debugfs interface (the counters) is inspired by the 
> original mips code. Pretty niche use case but can be handy at times...

Right, I see what it does now, and I agree that this is not a problem.
A tracepoint is probably an even better way to handle this flexibly,
but since it's not a stable interface either way, this can be optimized
later on.

       Arnd