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