linux-kernel - RE: printk: Add process name information to printk() output.

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Date:   Fri, 4 Sep 2020 18:31:13 +0900
From:   김창기 <changki.kim@...sung.com>
To:     "'Greg KH'" <gregkh@...uxfoundation.org>
Cc:     <pmladek@...e.com>, <sergey.senozhatsky@...il.com>,
        <rostedt@...dmis.org>, <john.ogness@...utronix.de>,
        <masahiroy@...nel.org>, <rd.dunlap@...il.com>, <krzk@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: RE: printk: Add process name information to printk() output.

> On Fri, Sep 04, 2020 at 05:24:38PM +0900, Changki Kim wrote:
> > Printk() meesages are the most basic and useful debug method.
> > However, additional information needs in multi-processor.
> > If we add messages with processor id and process name, we can find a
> > problem only with messages when the problem occurs with H/W IP or CPU.
> > This is very useful in narrowing down the scope of the problems.
> >
> > Therefore, instead of trying to help buffering, let's try to help
> > reconstructing messages by saving caller information as of calling
> > log_store() and adding it as "[$processor_id: $process_name:
> $thread_id]"
> > upon printing to consoles.
> >
> > Some examples for console output:
> >
> >   [    0.059580] [0:      swapper/0:    1] CPU: All CPU(s) started at
EL1i
> >   [    2.153157] [5:           init:    1] migov: complete to probe
migov
> >   [    7.441317] [4:           init:    1] NET: Registered protocol
family 39
> >   [   22.793389] [5:  kworker/u16:1:  184] SMP: stopping secondary CPUs
> >
> > Signed-off-by: Changki Kim <changki.kim@...sung.com>
> > ---
> >  kernel/printk/printk.c            | 20 ++++++++++++++++++--
> >  kernel/printk/printk_ringbuffer.h |  7 +++++++
> >  lib/Kconfig.debug                 | 16 ++++++++++++++++
> >  3 files changed, 41 insertions(+), 2 deletions(-)
> 
> Isn't the CPU number already present if you want it today?  Why add it
> again?
> 
> thanks,
> 
> greg k-h

CPU number isn't present now. If I enabled PRINTK_CALLER,
then it is present cpu id or thread id.
The config isn't always present cpu id.
We need cpu id each each message.

Thanks.