linux-kernel - Re: How to disable tracing at runtime from the Linux kernel command line?

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Message-ID: <20180414123009.6d86d0f9@gandalf.local.home>
Date:   Sat, 14 Apr 2018 12:30:09 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Paul Menzel <pmenzel+linux-tracing@...gen.mpg.de>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: How to disable tracing at runtime from the Linux kernel command
 line?

On Sat, 14 Apr 2018 15:09:33 +0200
Paul Menzel <pmenzel+linux-tracing@...gen.mpg.de> wrote:

> Dear Linux folks,
> 
> 
> I am trying to reduce the boot time of a standard Linux distribution 
> kernel. Currently, distributions – at least Debian und Ubuntu – enable 
> function tracing.
> 
> ```
> CONFIG_FTRACE=y
> CONFIG_FUNCTION_TRACER=y
> CONFIG_FUNCTION_GRAPH_TRACER=y
> 
> CONFIG_EVENT_TRACING=y
> ```
> 
> This is great, as it makes it easy to use tracing to hunt down things 
> holding up the boot. But it also skews the boot time quite a lot.
> 
> ```
> $ sudo dmesg
> […]
> [    0.318412] initcall init_graph_trace+0x0/0x64 returned 0 after 
> 199218 usecs
> […]
> [    1.770287] calling  event_trace_init+0x0/0x2c2 @ 1
> [    2.052871] initcall event_trace_init+0x0/0x2c2 returned 0 after 
> 275942 usecs
> […]
> ```
> 
> Is there a way to disable tracing on the Linux kernel command line to 
> disable tracing?
> 

Try initcall_blacklist. But you acquire all risks when doing so. I
never tried it, so I have no idea what side effects that may have.

-- Steve