Starting JFR with -Xlog:jfr=info reveals the following log output:

[0.448s][info][jfr] Flight Recorder initialized
[0.449s][info][jfr] Repository base directory: C:\Users\egahlin\AppData\Local\Temp
[0.504s][info][jfr] Creating thread sampler for java:20 ms, native 0 ms
[0.505s][info][jfr] Enrolling thread sampler
[0.506s][info][jfr] Enrolling thread sampler
[0.507s][info][jfr] Updated thread sampler for java: 20 ms, native 0 ms
[0.508s][info][jfr] Updated thread sampler for java: 20 ms, native 0 ms
[0.509s][info][jfr] Updated thread sampler for java: 20 ms, native 20 ms
[0.523s][info][jfr] Started recording "1" (1)
[0.614s][info][jfr] Updated thread sampler for java: 0 ms, native 20 ms
[0.614s][info][jfr] Disenrolling thread sampler
[0.617s][info][jfr] Stopped recording "1" (1). Reason "Shutdown".
[0.622s][info][jfr] Removed repository C:\Users\egahlin\AppData\Local\Temp\2020_02_06_20_36_29_8184

The thread sampler is an implementation detail and should have log level debug or trace.