Chapter 29. Adding and removing tracepoints from a running perf collector without stopping or restarting perf

Procedure

1. Configure the control pipe interface:

   # mkfifo control ack perf.pipe

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

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

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

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

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

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   Starting the read side of the control pipe triggers the following message in the first terminal:

   Events disabled

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4. In a third terminal, enable a tracepoint using the control file:

   # echo 'enable sched:sched_process_fork' > control

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   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 terminal:

   event sched:sched_process_fork enabled

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   Once the tracepoint is enabled, the second terminal 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

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