tools/cpudist: Fix concurrency issue caused by idle threads & Exclude CPU idle time by default

[xingfeng2510]

1. Fix concurrency issue caused by idle threads

Like #2804, #3740, pid as key not be suitable for multiple idle threads (pid = 0), which may lead to incorrect delta time. Combines cpu and pid as unique key to avoid this issue.

2. Exclude CPU idle time by default

Currently, cpudist includes CPU idle time by default. When idle threads (pid = 0) mixed with other threads (pid != 0), the output of cpudist is not clear enough, CPU time distribution of idle threads are usually very large on a not busy system (hundreds of milliseconds, even > 1s).

For example：

# ./cpudist.py -Tm 1

14:45:36
     msecs               : count     distribution
         0 -> 1          : 676      |****************************************|
         2 -> 3          : 18       |*                                       |
         4 -> 7          : 119      |*******                                 |
         8 -> 15         : 74       |****                                    |
        16 -> 31         : 52       |***                                     |
        32 -> 63         : 175      |**********                              |
        64 -> 127        : 34       |**                                      |
       128 -> 255        : 9        |                                        |
       256 -> 511        : 10       |                                        |
       512 -> 1023       : 11       |                                        |
      1024 -> 2047       : 3        |                                        |
      2048 -> 4095       : 36       |**                                      |

14:45:37
     msecs               : count     distribution
         0 -> 1          : 739      |****************************************|
         2 -> 3          : 12       |                                        |
         4 -> 7          : 115      |******                                  |
         8 -> 15         : 76       |****                                    |
        16 -> 31         : 46       |**                                      |
        32 -> 63         : 191      |**********                              |
        64 -> 127        : 39       |**                                      |
       128 -> 255        : 2        |                                        |
       256 -> 511        : 7        |                                        |
       512 -> 1023       : 18       |                                        |

As #2166, exclude CPU idle time by default, simply check whether pid == 0. Add option -I to include CPU idle time (same as before).

Also, runqlat excludes idle threads directly (#1741).

After excluding CPU idle time by default, for example, the output looks simple and clear:

# ./cpudist.py -Tm 1

14:48:02
     msecs               : count     distribution
         0 -> 1          : 519      |****************************************|
         2 -> 3          : 1        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 2        |                                        |

14:48:03
     msecs               : count     distribution
         0 -> 1          : 540      |****************************************|
         2 -> 3          : 1        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 2        |                                        |

@yonghong-song @brendangregg Please take a look this patch, thanks!

[yonghong-song]

Agree that by default we should exclude idle task as the tool's main purpose is to cpu usage distribution for non-idle useful tasks.