These events only show if a thread has been removed from the CPU, but
doesn't provide information about what other thread caused the context
switch. This type of information can be obtained even with strict
/proc/sys/kernel/perf_event_paranoid settings.
The region of past events must be enclosed by the OU[ and OU] events and
all the events within the region must be sorted. The sorting mechanism
looks back up to 10000 events, so it may fail if they are too far away
in the past.
