I'm mass filing large ticket items from FHR's performance review: https://wiki.mozilla.org/Performance/FHR. This bug is for the first item: 8. Telemetry probes FHR should track its first-run initialization time in Telemetry separately from subsequent initialization times. We should also change the existing Telemetry probes to accurately track the amount of time spent on FHR operations instead of tracking the wall clock time elapsed from issuing an asynchronus FHR operation to the operation's completion handler running. It's causing the probes to over-estimate the amount of time required by FHR operations.

I think this is worth doing sooner rather than later.

> HR should track its first-run initialization time in > Telemetry separately from subsequent initialization times. We already do this. > We should also > change the existing Telemetry probes to accurately track the amount of time > spent on FHR operations instead of tracking the wall clock time elapsed from > issuing an asynchronus FHR operation to the operation's completion handler > running. It's causing the probes to over-estimate the amount of time > required by FHR operations. The operations being measured often consist of many (dozens) of individual async operations. Most of the time spent on these operations is in background threads (e.g. SQLite I/O or Necko requests). It would be extremely difficult and code invasive to isolate actual times and not wall clock time. Probing all the code would likely involve obtaining hundreds of Date.now() and computing deltas. There would certainly be a probing overhead here. I just don't think the requested task is possible without essentially inventing an ad-hoc profiler. Because of this, I think we should mark WONTFIX or WORKSFORME.

FHR is going away per bug 1209088, wontfix.