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