From: Michael Jeanson via lttng-dev <lttng-dev@lists.lttng.org>
To: Benjamin Saint-Cyr <benjamin.saint-cyr@polymtl.ca>
Cc: lttng-dev <lttng-dev@lists.lttng.org>
Subject: Re: [lttng-dev] Seeking Assistance on LTTng for Kubernetes Performance Research
Date: Wed, 12 Apr 2023 14:29:38 -0400 [thread overview]
Message-ID: <8c167748-42bd-9959-0e33-03bc24e22f95@efficios.com> (raw)
In-Reply-To: <20230406195630.Horde.jhBZfsMqxFud8S3napU7CjJ@www.imp.polymtl.ca>
On 2023-04-06 15:56, Benjamin Saint-Cyr via lttng-dev wrote:
> 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?
The PID namespace context is probably the closest thing to what you are
looking for, see
"https://lttng.org/man/3/lttng-ust/v2.13/#doc-_context_information". The
hierachy of the namespaces can be recorded in a statedump.
>
> 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 don't think we have anything cgroup related in the statedump at the moment,
not that it's impossible but it was never implemented.
>
> 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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prev parent reply other threads:[~2023-04-12 18:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-06 19:56 [lttng-dev] Seeking Assistance on LTTng for Kubernetes Performance Research Benjamin Saint-Cyr via lttng-dev
2023-04-12 18:29 ` Michael Jeanson via lttng-dev [this message]
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