Chapter 20. Managing tracepoints by using perf collector without restarting perf

Procedure

1. Configure the control pipe interface:

   # mkfifo control ack perf.pipe

2. Run perf record with the control file configuration and events you are interested in enabling:

   # perf record --control=fifo:control,ack -D -1 --no-buffering -e 'sched:*' -o - > perf.pipe

   In this example, declaring 'sched:*' after the -e option starts perf record with scheduler events.

3. In a second command line, start the read side of the control pipe:

   # cat perf.pipe | perf --no-pager script -i -

4. Starting the read side of the control pipe triggers the following message in the first command line:

   Events disabled

5. In a third command line, enable a tracepoint by using the control file:

   # echo 'enable sched:sched_process_fork' > control

   This command triggers perf to scan the current event list in the control file for the declared event. If the event is present, the tracepoint is enabled and the following message appears in the first command line:

   event sched:sched_process_fork enabled

6. Once the tracepoint is enabled, the second command line displays the output from perf detecting the tracepoint:

   bash 33349 [034] 149587.674295: sched:sched_process_fork: comm=bash pid=33349 child_comm=bash child_pid=34056