1================ 2NMI Trace Events 3================ 4 5These events normally show up here: 6 7 /sys/kernel/debug/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/debug/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/debug/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