lttng-ust vs modules timestamp correlation is sensitive to load at trace start
lttng-ust timestamp correlation between monotonic time and real time is sampled at trace start from the context of the session daemon (since 2.2).
For per-UID buffer, this correlation is taken whenever a new UST UID shows up in the trace.
For per-PID buffers, this correlation is taken whenever a new UST PID shows up.
The correlation is needed when merging traces from different UIDs/PIDs, between UST and kernel traces, and between hosts.
The current correlation algorithm is prone to be imprecise due to preemption of the sessiond that could happen if the system is under high load when the correlation is performed.