linux-kernel - Re: [PATCH] tracing: Have large events show up as '[LINE TOO BIG]' instead of nothing

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Message-Id: <20231211210819.cd4f7b3df09cf0eb584e51b9@kernel.org>
Date:   Mon, 11 Dec 2023 21:08:19 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] tracing: Have large events show up as '[LINE TOO BIG]'
 instead of nothing

On Sun, 10 Dec 2023 10:34:15 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sun, 10 Dec 2023 09:11:40 -0500
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
> > On 2023-12-09 17:10, Steven Rostedt wrote:
> > [...]
> > >              <...>-852     [001] .....   121.550551: tracing_mark_write[LINE TOO BIG]
> > >              <...>-852     [001] .....   121.550581: tracing_mark_write: 78901234  
> > 
> > Failing to print an entire message because it does not fit in the
> > buffer size is rather inconvenient.
> 
> Yes I agree, and luckily it hasn't been called out as an issue. Note, I hit
> this because I extended the trace_marker buffer before increasing the
> trace_seq size. Otherwise, the trace_marker just breaks it up. This can now
> only be triggered by internal changes.

Rather than the broken output, I would perfer this output.

> 
> > 
> > It would be better to print the partial line, and end the line with
> > a <TRUNCATED LINE> tag.

But how long the partial line length is good enough? I think that big (and long)
user marker maybe not for human, so we don't need to care about readability.
I think current one is one of better solutions.

So I'll give my Reviewed-by. :)

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thank you,

> 
> Agreed, but I don't have time to do that (I already spent way too much time
> on this than I had allocated). I decided to just do what the trace_pipe
> currently does, and leave "print partial line" to another day when I can
> allocate time on this.
> 
> Hmm, this could be added to the "TODO" list that was talked about in
> ksummit-discuss.
> 
> -- Steve
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>