linux-kernel - Re: [PATCH] trace/ring_buffer: remove unused arguments

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Date:   Thu, 20 Oct 2022 23:25:56 +0800
From:   chensong <chensong_2000@....cn>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     mingo@...hat.com, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org, xiehuan09@...il.com
Subject: Re: [PATCH] trace/ring_buffer: remove unused arguments

Hi,

On 2022/10/20 下午10:15, Steven Rostedt wrote:
> On Thu, 20 Oct 2022 22:06:51 +0800
> Song Chen <chensong_2000@....cn> wrote:
> 
>> As a argument, event has nothing to do with either
>> ring_buffer_unlock_commit or rb_commit and cleaning
>> it up has no side effect.
> 
> OK, so this is because of a389d86f7fd0 ("ring-buffer: Have nested events
> still record running time stamp") which removed the usage of event in rb_commit():
> 
>   static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
>                        struct ring_buffer_event *event)
>   {
>          local_inc(&cpu_buffer->entries);
> -       rb_update_write_stamp(cpu_buffer, event);
>          rb_end_commit(cpu_buffer);
>   }
> 
> 
> I guess this doesn't hurt.
> 
> -- Steve
> 

I was reading __kprobe_trace_func, store_trace_args stores args in 
fbuffer.entry,which is event->array, but at the end, rb_commit uses 
fbuffer.buffer instead of event.

Then i thought, if it's useless, why not just clean it up.

Song

>>
>> Signed-off-by: Song Chen <chensong_2000@....cn>
>> ---
>>   include/linux/ring_buffer.h          |  3 +--
>>   kernel/trace/ring_buffer.c           | 12 +++++-------
>>   kernel/trace/ring_buffer_benchmark.c |  2 +-
>>   kernel/trace/trace.c                 |  2 +-
>>   4 files changed, 8 insertions(+), 11 deletions(-)
>