1================
2NMI Trace Events
3================
4
5These events normally show up here:
6
7	/sys/kernel/tracing/events/nmi
8
9
10nmi_handler
11-----------
12
13You might want to use this tracepoint if you suspect that your
14NMI handlers are hogging large amounts of CPU time.  The kernel
15will warn if it sees long-running handlers::
16
17	INFO: NMI handler took too long to run: 9.207 msecs
18
19and this tracepoint will allow you to drill down and get some
20more details.
21
22Let's say you suspect that perf_event_nmi_handler() is causing
23you some problems and you only want to trace that handler
24specifically.  You need to find its address::
25
26	$ grep perf_event_nmi_handler /proc/kallsyms
27	ffffffff81625600 t perf_event_nmi_handler
28
29Let's also say you are only interested in when that function is
30really hogging a lot of CPU time, like a millisecond at a time.
31Note that the kernel's output is in milliseconds, but the input
32to the filter is in nanoseconds!  You can filter on 'delta_ns'::
33
34	cd /sys/kernel/tracing/events/nmi/nmi_handler
35	echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter
36	echo 1 > enable
37
38Your output would then look like::
39
40	$ cat /sys/kernel/tracing/trace_pipe
41	<idle>-0     [000] d.h3   505.397558: nmi_handler: perf_event_nmi_handler() delta_ns: 3236765 handled: 1
42	<idle>-0     [000] d.h3   505.805893: nmi_handler: perf_event_nmi_handler() delta_ns: 3174234 handled: 1
43	<idle>-0     [000] d.h3   506.158206: nmi_handler: perf_event_nmi_handler() delta_ns: 3084642 handled: 1
44	<idle>-0     [000] d.h3   506.334346: nmi_handler: perf_event_nmi_handler() delta_ns: 3080351 handled: 1
45
46