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

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Message-ID: <2466c45d-8d77-6d57-58e2-cb1897034e2e@molgen.mpg.de>
Date:   Sat, 14 Apr 2018 15:09:33 +0200
From:   Paul Menzel <pmenzel+linux-tracing@...gen.mpg.de>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org
Subject: How to disable tracing at runtime from the Linux kernel command line?

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?

Kind regards,

Paul