|author||Steven Rostedt (Red Hat) <firstname.lastname@example.org>||2014-12-12 22:27:10 -0500|
|committer||Steven Rostedt <email@example.com>||2014-12-15 10:17:38 -0500|
|parent||tracing: Move enabling tracepoints to just after rcu_init() (diff)|
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 <firstname.lastname@example.org> Tested-by: Thomas Gleixner <email@example.com> Acked-by: Thomas Gleixner <firstname.lastname@example.org> Signed-off-by: Steven Rostedt <email@example.com>
Diffstat (limited to 'Documentation')
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 1d09eb37c562..ae41f1181e9a 100644
@@ -3500,6 +3500,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
See also Documentation/trace/ftrace.txt "trace options"
+ 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
+ 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.
[FTRACE] enable this option to disable tracing when a
warning is hit. This turns off "tracing_on". Tracing can