linux-kernel - Re: [PATCH] tracing: document buffer_size

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Message-ID: <e89de62e-e19a-1eeb-d180-a308cbf97c03@arm.com>
Date:   Tue, 3 Oct 2023 16:01:30 +0100
From:   Christian Loehle <christian.loehle@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Zheng Yejian <zhengyejian1@...wei.com>, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH] tracing: document buffer_size_kb more precisely

On 02/10/2023 16:09, Steven Rostedt wrote:
> On Tue, 26 Sep 2023 11:38:14 +0100
> Christian Loehle <christian.loehle@....com> wrote:
> 
>>>> @@ -191,7 +191,7 @@ of ftrace. Here is a list of some of the key files:
>>>>       A few extra pages may be allocated to accommodate buffer management
>>>>       meta-data. If the last page allocated has room for more bytes
>>>>       than requested, the rest of the page will be used,
>>>> -    making the actual allocation bigger than requested or shown.
>>>> +    making the actual allocation bigger than requested.  
>>>
>>> Hi, the actual allocation should still be bigger than shown due to the
>>> loss of accuracy when doing unit conversion from bytes to kilobytes (see
>>> tracing_entries_read()).
>>>   
>> Right, the sysfs obviously only allows for KB aligned setting, but you're right.
>> If set on the cmdline non-KB multiples are possible and accuracy is lost.
>> Nevermind then.
> 
> I'm assuming this patch can be dropped?
> 
> -- Steve
Yes please drop it, there's probably still some room for improvement for clarity,
but this patch is not correct.