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