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

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Message-ID: <20200904090535.GA2440145@kroah.com>
Date:   Fri, 4 Sep 2020 11:05:35 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Changki Kim <changki.kim@...sung.com>
Cc:     pmladek@...e.com, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, john.ogness@...utronix.de,
        changbin.du@...el.com, 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