Hello fellow LTTNG devs,
We are students from Polytechnique Montreal and we are currently working
on an TraceCompass analysis module for Linux containers
(LXC/Docker/Etc...). The information we track is mostly CPU usage by pid
namespace, which would allow the identification of CPU-utilization
related bottlenecks on a Linux container host.
We tried to come up with targeted information to recreate the
container/PID namespace tree of a Linux host and we have modified
lttng-modules to be able to do so :
https://github.com/Selora/lttng-modules
In our analysis, we try to re-use as many information that was already
available in the LTTNG kernel tracer. We build our container/namespace
tree using the tasks and their parent recursively (using only the
pid/vppid/ppid). However, we were unable to have a reliable model
without some light modifications on some tracepoints.
_/
The modifications to the lttng-modulues where the following:/_
We added the PID namespace INode (from /proc/PID/ns/pid) to the LTTNG
statedump tracepoint.
Also, to track new task/containers that would spawn during the tracing
session, we also added multiple fields to the /sched_process_fork/ event :
* Added a VTID field for the children task. This is mandatory in our
analysis, as we keep track of VTID/TID association.
* Added a/parent_ns_inum/ and /child_ns_inum/ field wich represent the
pid namespaces inodes of the parent and child task respectively.
o The /parent_ns_inum/ is "not mandatory" in our analysis, but it
keeps things simple as we don't have to track TID from parent
containers and it keeps the code relatively independant wheter
statedump is enabled or not.
o The /child_ns_inum///IS mandatory, because even if we keep track
of the PID/VPID/PPID/VPPID that have spawned, it is possible to
"inject" a task in an already existing namespace without
repareting it to the child reaper of the container (this means
the task is sent in a namespace, but it is not part of the
process tree of the container of that namespace)
We hope to integrate our analysis to TraceCompass soon, and without the
modification to the LTTNG tracer approved, we would be unable to proceed
throught code review.
We would be really grateful to the community if we could have feedback,
and we will make every modifications possibles to have our analysis up
and working!
The code is supposed to work on kernel version 3.8 through 3.19.
It was tested on 3.18 and 3.19, and I'am going to test it for 3.8 today.
Cheers,
Sebastien & Francis.
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