samples/bpf: Add program for CPU state statistics

samples/bpf: Add program for CPU state statistics

CPU is active when have running tasks on it and CPUFreq governor can
select different operating points (OPP) according to different workload;
we use 'pstate' to present CPU state which have running tasks with one
specific OPP.  On the other hand, CPU is idle which only idle task on
it, CPUIdle governor can select one specific idle state to power off
hardware logics; we use 'cstate' to present CPU idle state.

Based on trace events 'cpu_idle' and 'cpu_frequency' we can accomplish
the duration statistics for every state.  Every time when CPU enters
into or exits from idle states, the trace event 'cpu_idle' is recorded;
trace event 'cpu_frequency' records the event for CPU OPP changing, so
it's easily to know how long time the CPU stays in the specified OPP,
and the CPU must be not in any idle state.

This patch is to utilize the mentioned trace events for pstate and
cstate statistics.  To achieve more accurate profiling data, the program
uses below sequence to insure CPU running/idle time aren't missed:

- Before profiling the user space program wakes up all CPUs for once, so
  can avoid to missing account time for CPU staying in idle state for
  long time; the program forces to set 'scaling_max_freq' to lowest
  frequency and then restore 'scaling_max_freq' to highest frequency,
  this can ensure the frequency to be set to lowest frequency and later
  after start to run workload the frequency can be easily to be changed
  to higher frequency;

- User space program reads map data and update statistics for every 5s,
  so this is same with other sample bpf programs for avoiding big
  overload introduced by bpf program self;

- When send signal to terminate program, the signal handler wakes up
  all CPUs, set lowest frequency and restore highest frequency to
  'scaling_max_freq'; this is exactly same with the first step so
  avoid to missing account CPU pstate and cstate time during last
  stage.  Finally it reports the latest statistics.

The program has been tested on Hikey board with octa CA53 CPUs, below
is one example for statistics result, the format mainly follows up
Jesper Dangaard Brouer suggestion.

Jesper reminds to 'get printf to pretty print with thousands separators
use %' and setlocale(LC_NUMERIC, "en_US")', tried three different arm64
GCC toolchains (5.4.0 20160609, 6.2.1 20161016, 6.3.0 20170516) but all
of them cannot support printf flag character %' on arm64 platform, so go
back print number without grouping mode.

CPU states statistics:
state(ms)  cstate-0    cstate-1    cstate-2    pstate-0    pstate-1    pstate-2    pstate-3    pstate-4
CPU-0      767         6111        111863      561         31          756         853         190
CPU-1      241         10606       107956      484         125         646         990         85
CPU-2      413         19721       98735       636         84          696         757         89
CPU-3      84          11711       79989       17516       909         4811        5773        341
CPU-4      152         19610       98229       444         53          649         708         1283
CPU-5      185         8781        108697      666         91          671         677         1365
CPU-6      157         21964       95825       581         67          566         684         1284
CPU-7      125         15238       102704      398         20          665         786         1197

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>