linux-kernel - Re: [PATCH -printk] printk, tracing: fix console tracepoint

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Message-ID: <YnU113/cOtv7k9tH@alley>
Date:   Fri, 6 May 2022 16:51:03 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Marco Elver <elver@...gle.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Johannes Berg <johannes.berg@...el.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Linux Kernel Functional Testing <lkft@...aro.org>
Subject: Re: [PATCH -printk] printk, tracing: fix console tracepoint

On Wed 2022-05-04 11:46:36, Petr Mladek wrote:
> On Tue 2022-05-03 21:20:44, John Ogness wrote:
> > On 2022-05-03, Marco Elver <elver@...gle.com> wrote:
> > > One notable difference is that by moving tracing into printk_sprint(),
> > > the 'text' will no longer include the "header" (loglevel and timestamp),
> > > but only the raw message. Arguably this is less of a problem now that
> > > the console tracepoint happens on the printk() call and isn't delayed.
> > 
> > Another slight difference is that messages composed of LOG_CONT pieces
> > will trigger the tracepoint for each individual piece and _never_ as a
> > complete line.
> > 
> > It was never guaranteed that all LOG_CONT pieces make it into the final
> > printed line anyway, but with this change it will be guaranteed that
> > they are always handled separately.
> > 
> > I am OK with this change, but like Steven, I agree the the users of that
> > tracepoint need to chime in.
> 
> My feeling is that the feature is not used much. Otherwise people
> would complain that it was asynchronous and hard to use.
> 
> I mean that the printk() messages appeared in the trace log
> asynchronously. So it required some post processing to correctly
> sort them against other tracing messages. The same result can be
> achieved by processing printk log buffer, dmesg.log, journalctl.
> 
> I guess that we will only find the answer when we push the change
> into linux-next and mainline. I am going to do so.

JFYI, the patch has been committed into printk/linux.git,
branch rework/kthreads.

Best Regards,
Petr