From mboxrd@z Thu Jan  1 00:00:00 1970
From: rostedt@goodmis.org (Steven Rostedt)
Date: Mon, 6 Aug 2012 09:39:17 -0400
Subject: [PATCH v3] printk: add option to print cpu id
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Message-ID: <20120806133917.GF16873@home.goodmis.org>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Aug 03, 2012 at 03:48:26PM -0700, Pandita, Vikram wrote:
> On Fri, Aug 3, 2012 at 3:36 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Fri, Aug 03, 2012 at 03:25:17PM -0700, Pandita, Vikram wrote:
> >> >> This was something that got used internally and helped at times.
> >> >
> >> > Could you have used the trace point instead?
> >>
> >> As i understood the trace_prink(), one would need to modify existing
> >> printk -> trace_printk. Is my understanding correct?
> >
> > No, you should just be able to watch the tracepoint, right?
> 
> yes.
> Assumption being you know _EXACTLY_ what code piece to watch for.
> Which may not be the case all times.

But it traces all printks.

 # echo 1 > /sys/kernel/debug/tracing/events/printk/console/enable
 # mount /home/rostedt
 # cat /sys/kernel/debug/tracing/trace
# tracer: nop
#
# entries-in-buffer/entries-written: 2/2   #P:4
#
#                              _-----=> irqs-off
#                             / _----=> need-resched
#                            | / _---=> hardirq/softirq
#                            || / _--=> preempt-depth
#                            ||| /     delay
#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
#              | |       |   ||||       |         |
        modprobe-2707  [002] d..1    97.079458: console: [   95.816945] NFS: Registering the id_resolver key type

        modprobe-2707  [002] d..1    97.084534: console: [   95.822038] Key type id_resolver registered

If you wanted this from boot up, you can just add to the kernel command line:

  trace_event=console

-- Steve