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

["chengjian (D)" <cj.chengjian@huawei.com>]

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...