• Leo Yan's avatar
    samples/bpf: Add program for CPU state statistics · c5350777
    Leo Yan authored
    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: 's avatarLeo Yan <leo.yan@linaro.org>
    Signed-off-by: 's avatarDaniel Borkmann <daniel@iogearbox.net>
    c5350777
cpustat_kern.c 7.01 KB