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| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2014-12-12 22:27:10 -0500 |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2014-12-15 10:17:38 -0500 |
| commit | 0daa2302968c13b657118d6ac92471f8fd2f3f28 (patch) | |
| tree | 8bea68f7bbeab6521c11c01f55b5660082eeedf6 /Documentation | |
| parent | 5f893b2639b21ffe6834b1aebba392c37d2b83f9 (diff) | |
| download | lwn-0daa2302968c13b657118d6ac92471f8fd2f3f28.tar.gz lwn-0daa2302968c13b657118d6ac92471f8fd2f3f28.zip | |
tracing: Add tp_printk cmdline to have tracepoints go to printk()
Add the kernel command line tp_printk option that will have tracepoints
that are active sent to printk() as well as to the trace buffer.
Passing "tp_printk" will activate this. To turn it off, the sysctl
/proc/sys/kernel/tracepoint_printk can have '0' echoed into it. Note,
this only works if the cmdline option is used. Echoing 1 into the sysctl
file without the cmdline option will have no affect.
Note, this is a dangerous option. Having high frequency tracepoints send
their data to printk() can possibly cause a live lock. This is another
reason why this is only active if the command line option is used.
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1412121539300.16494@nanos
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/kernel-parameters.txt | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 1d09eb37c562..ae41f1181e9a 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3500,6 +3500,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted. See also Documentation/trace/ftrace.txt "trace options" section. + tp_printk[FTRACE] + Have the tracepoints sent to printk as well as the + tracing ring buffer. This is useful for early boot up + where the system hangs or reboots and does not give the + option for reading the tracing buffer or performing a + ftrace_dump_on_oops. + + To turn off having tracepoints sent to printk, + echo 0 > /proc/sys/kernel/tracepoint_printk + Note, echoing 1 into this file without the + tracepoint_printk kernel cmdline option has no effect. + + ** CAUTION ** + + Having tracepoints sent to printk() and activating high + frequency tracepoints such as irq or sched, can cause + the system to live lock. + traceoff_on_warning [FTRACE] enable this option to disable tracing when a warning is hit. This turns off "tracing_on". Tracing can |