On 2023-08-13 10:58, Bala Gundeboina via lttng-dev wrote:
Hi,
I am Using LTTng in my project , I am recording a kernel session for
long duration (eg more than 15minutes) I am enabling all the events for
recording but some events discarding after stopping the session, if i
run more than 5 minutes only some events are discarding. I have tried to
change in the .ltttngrc file also to increase buffer-size.
lttng destroy
Destroying session `my-kernel-session`...
Session `my-kernel-session` destroyed
Warning: 94424667 events were discarded, please refer to the
documentation on channel configuration
Hello Bala,
Based on my understanding of the scenario, discarded events are to be
expected. Rather than trying to avoid discarded events, I would
recommend adjusting how much data is being collected. In most tracing
use cases, it is not relevant to enable all kernel tracepoints for a
long period of time (e.g. several minutes) as it can quickly generate an
enormous amount of noisy data that is nearly impossible to sort through.
As a reference, a busy 8 core machine could generate 100 MB/s of data.
Typically when trying to understand a problem in detail with tracing,
you would start with a very small number of tracepoints enabled for a
longer period of time (with the goal of developing a high-level
understanding of when/where the problem is happening). Then as you
iteratively narrow down when/where the problem happens you can gradually
increase the number of relevant tracepoints without being overwhelmed
with data.
A general rule of thumb is that if you're storing trace data for a long
period of time (e.g. more than a minute) then very few tracepoints
should be enabled (e.g. 2-5). Maximum tracing detail would typically
only be used to trace for a couple seconds (or ideally less if you can
automate starting and stopping tracing).
Here are some general references about tracing strategy:
- Whether tracing is the appropriate approach:
https://github.com/tuxology/tracevizlab/tree/master/labs/001-what-is-tracing#when-to-trace
- Iterative investigation, selecting tracepoints:
https://wiki.linuxfoundation.org/realtime/documentation/howto/debugging/debug-steps
(Recommended sections: Isolate the source, Trace detail)
Hope this helps!
Best,
Erica
actually when i am running below command i am getting below warning i am
thinking this is the issue because sometimes this warning is not coming
that i didn't seen discarded events. how to overcome this problem can
you provide some detailed
lttng-sessiond --daemonize
Warning: Failed to produce a random seed using getrandom(), falling back
to pseudo-random device seed generation which will block until its pool
is initialized: Failed to get true random data using getre
At first glance, this error seems unrelated to whether or not events are
discarded.
Thanks & Regards
Bala Gundeboina
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