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