Dear LTTng Developers,
I am currently conducting performance research on Kubernetes for my
master's thesis and am using LTTng for data collection and Trace
Compass for analysis. I have a couple of questions and concerns, and I
would appreciate your guidance to ensure I am using your tools
effectively.
1. In the Control Flow view, I can see the CPU throttling due to the
quota defined in the Cgroup as the pod runs and then waits for the CPU
periodically. However, it is unclear whether the pod is waiting due to
a full CPU or because of timeshares. I can easily find this
information in /sys/fs/cgroup/cpu,cpuacct/kubepods/<burstable or
besteffort>/pod<UID>/cpu.stat if the pod is being throttled. Is there
a way to extract this information using LTTng or Trace Compass?
2. I am attempting to determine which PID is running a specific
Container/Pod UID. Currently, I can deduce this by observing the
process named runc[*:INIT], as it creates the cgroup and clones the
process for the container. However, this approach is fragile and only
works due to an implementation detail. It also fails if tracing starts
after deployment. This information is easily available in
/sys/fs/cgroup/cpu,cpuacct/kubepods/<burstable or
besteffort>/pod<UID>/<container ID>/cgroup.procs. Is there an existing
method within LTTng to obtain this information that I may not be aware
of?
I have been informed that it might be possible to read the information
in cpu.stat or cgroup.procs using a state dump at the beginning or
end, but the process remains unclear. Alternatively, I could
instrument the kernel or the process handling the accounting, but this
would be quite challenging. Another option would be to use something
similar to cAdvisor, but its efficiency is questionable since it
dedicates an entire process to reading a few files.
I would greatly appreciate any guidance or suggestions you may have on
improving my approach and effectively utilizing LTTng for my research.
Thank you for your time and assistance.
Best regards,
Benjamin Saint-Cyr
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