Commit | Line | Data |
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0c4df02d DH |
1 | NMI Trace Events |
2 | ||
3 | These events normally show up here: | |
4 | ||
5 | /sys/kernel/debug/tracing/events/nmi | |
6 | ||
7 | -- | |
8 | ||
9 | nmi_handler: | |
10 | ||
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: | |
14 | ||
15 | INFO: NMI handler took too long to run: 9.207 msecs | |
16 | ||
17 | and this tracepoint will allow you to drill down and get some | |
18 | more details. | |
19 | ||
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: | |
23 | ||
24 | $ grep perf_event_nmi_handler /proc/kallsyms | |
25 | ffffffff81625600 t perf_event_nmi_handler | |
26 | ||
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': | |
31 | ||
32 | cd /sys/kernel/debug/tracing/events/nmi/nmi_handler | |
33 | echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter | |
34 | echo 1 > enable | |
35 | ||
36 | Your output would then look like: | |
37 | ||
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 | |
43 |