Re: [PATCH] perf/ftrace : Fix repetitious traces when specify a target task

[chengjian (D)]

On 2017/10/10 19:33, Peter Zijlstra wrote:
> No, this _cannot_ be right. The whole point of the @task argument was to
> deliver the event multiple times -- maybe not to the same event, but it
> needs to be delivered multiple times in some cases. Therefore this is
> broken.
>
> But now you've got me looking at 75e8387685f6, which also looks
> completely insane.
> .
the demo is like this

```cpp
// bug_fork.c
#include <stdio.h>
#include <stdlib.h>

#include <unistd.h>


int main(int argc,char** argv){
    pid_t        pid;

    printf("parent pid = %d\n", getpid( ));

    pid = fork( );

    if(pid < 0)
    {
        perror("fork error");
        exit(-1);
    }
    else if(pid == 0)//  fork return 0 in child process
    {
        printf("child pid = %d\n", getpid( ));
        exit(0);
    }
    else        //  return child pid in parent process
    {
        //sleep(1);
        //count++;
    }

    return EXIT_SUCCESS;
}
```


the parent only wakeup_new child process once, but perf match a lot when 
use per-cpu maped.

In my opition, perf stat use per-thread-map, it will match twice.
sudo perf stat -e sched:sched_wakeup_new ./bug_fork

    parent pid = 86155
    child pid = 86156

    Performance counter stats for './bug_fork':

                 2      sched:sched_wakeup_new

       0.001112926 seconds time elapsed


Does it meen a match for trace parent(86155), a match for trace child(86156)

and what cases should the events be delivered multiple times?


Thanks...