[lttng-dev] lttng_ust_cyg_profile

[Alok Priyadarshi]

I am trying to collect a trace for visualizing callstack using
lttng_ust_cyg_profile.

Even though I have compiled a single source file with
-finstrument-functions, I guess it is producing too many events to
considerably slow down the instrumented process and cause lost events.

I am using clang, which does not support
-finstrument-functions-exclude-file-list. Is there any way to
filter lttng_ust_cyg_profile events before they are written to the trace? I
have tried various things:
1. lttng-track to only track one process

2. Only enable lttng_ust_cyg_profile:* events

3. Increase the subbuffer size:
lttng enable-channel --userspace --buffers-pid --subbuf-size=2M
--num-subbuf=2 mychannel
Using this option is very flaky however. It crashes lttng-sessiond.

Any other ideas to filter events?

I am also open to explicitly adding tracepoints to the functions I care
about. But I am not sure how they can be visualized in trace-compass
callstack view. I guess it only supports tracepoints generated by
lttng_ust_cyg_profile?
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