A.3. Capturing Trace Data on a Constant Basis Using the Systemtap Flight Recorder

Procedure A.1. Configuring and running systemtap

1. Install the package

   Install the systemtap-initscript package by running the following command:

   # yum install systemtap-initscript

2. Copy the configuration file

   Copy the systemtap scripts and the configuration files to the systemtap directory by running the following commands:

   # cp /usr/share/qemu-kvm/systemtap/script.d/qemu_kvm.stp /etc/systemtap/script.d/
   # cp /usr/share/qemu-kvm/systemtap/conf.d/qemu_kvm.conf /etc/systemtap/conf.d/

   The set of trace events to enable is given in qemu_kvm.stp. This SystemTap script can be customized to add or remove trace events provided in /usr/share/systemtap/tapset/qemu-kvm-simpletrace.stp.
   SystemTap customizations can be made to qemu_kvm.conf to control the flight recorder buffer size and whether to store traces in memory only or in the disk as well.

3. Start the service

   Start the systemtap service by running the following command:

   # systemctl start systemtap qemu_kvm

4. Make systemtap enabled to run at boot time

   Enable the systemtap service to run at boot time by running the following command:

   # systemctl enable systemtap qemu_kvm

5. Confirmation the service is running

   Confirm that the service is working by running the following command:

   # systemctl status systemtap qemu_kvm
   qemu_kvm is running...
   

Procedure A.2. Inspecting the trace buffer

1. Create a trace buffer dump file

   Create a trace buffer dump file called trace.log and place it in the tmp directory by running the following command:

   # staprun -A qemu_kvm >/tmp/trace.log

   You can change the file name and location to something else.

2. Start the service

   As the previous step stops the service, start it again by running the following command:

   # systemctl start systemtap qemu_kvm

3. Convert the trace contents into a readable format

   To convert the trace file contents into a more readable format, enter the following command:

   # /usr/share/qemu-kvm/simpletrace.py --no-header /usr/share/qemu-kvm/trace-events /tmp/trace.log