path: root/Documentation
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authorLinus Torvalds <torvalds@linux-foundation.org>2014-12-16 12:53:59 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-16 12:53:59 -0800
commita7c180aa7e76a55642e8492f28353303a50292c2 (patch)
treeb80b3575f1717a5e3a07081b5c9409805662490d /Documentation
parentMerge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/cooloney/linux-leds (diff)
parenttracing: Add tp_printk cmdline to have tracepoints go to printk() (diff)
Merge tag 'trace-3.19-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing updates from Steven Rostedt: "As the merge window is still open, and this code was not as complex as I thought it might be. I'm pushing this in now. This will allow Thomas to debug his irq work for 3.20. This adds two new features: 1) Allow traceopoints to be enabled right after mm_init(). By passing in the trace_event= kernel command line parameter, tracepoints can be enabled at boot up. For debugging things like the initialization of interrupts, it is needed to have tracepoints enabled very early. People have asked about this before and this has been on my todo list. As it can be helpful for Thomas to debug his upcoming 3.20 IRQ work, I'm pushing this now. This way he can add tracepoints into the IRQ set up and have users enable them when things go wrong. 2) Have the tracepoints printed via printk() (the console) when they are triggered. If the irq code locks up or reboots the box, having the tracepoint output go into the kernel ring buffer is useless for debugging. But being able to add the tp_printk kernel command line option along with the trace_event= option will have these tracepoints printed as they occur, and that can be really useful for debugging early lock up or reboot problems. This code is not that intrusive and it passed all my tests. Thomas tried them out too and it works for his needs. Link: http://lkml.kernel.org/r/20141214201609.126831471@goodmis.org" * tag 'trace-3.19-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: tracing: Add tp_printk cmdline to have tracepoints go to printk() tracing: Move enabling tracepoints to just after rcu_init()
Diffstat (limited to 'Documentation')
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 1de833556d22..bda85f1dbd44 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3570,6 +3570,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
See also Documentation/trace/ftrace.txt "trace options"
+ 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.
[FTRACE] enable this option to disable tracing when a
warning is hit. This turns off "tracing_on". Tracing can