1794652 - Consider removing "insufficient" page load timing probes like TIME_TO_*

Status: NEW

(Core :: Performance Engineering, task, P3)

Description

[Michael Comella (:mcomella) [NI reported issues only: ex-Mozilla]]

In the commit summary for bug 1671729, :denispal suggests:

Current page load telemetry probes are insufficient in performance RUM testing. FX_PAGE_LOAD_MS_2 will stop the timer when the user switches tabs or navigates off the page, while the current navigation probes [ed: including TIME_TO_*] include all content including about:blank, about:newtab, moz-extension, etc.

:denispal implemented PERF_* probes to replace them.

Looking at the bugs listed for the implementation of TIME_TO_DOM_COMPLETE_MS – bug 1344893, bug 1489524, bug 1580077 – this probe appears to have been initially implemented for performance monitoring purposes so I speculate the others are as well.

If, as :denispal suggests, these probes are insufficient for performance RUM, are they useful to anyone? We should answer that question and consider removing them. The most important reason is to avoid confusion when analyzing performance telemetry. There are currently 11 TIME_TO_* probes, plus some FX_* probes I didn't look into.

If we remove them, make sure we have appropriate replacements for all of the measurements we want to take. This is especially true for Android where probes are not transmitted by default: we have to explicitly make sure the replacement probes are exported.

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:denispal, does this seem like a reasonable thing to do?

Comment 1

[Michael Comella (:mcomella) [NI reported issues only: ex-Mozilla]]

If we want to investigate removing them but we don't have time to to do so, it might be useful to link to this issue from the description in each of the probes so someone using those probes has a chance of being aware of this context.

Comment 2

[Denis Palmeiro [:denispal]]

I think it's fair to remove these.