Show the Start time relative to "Navigation::Start" in the Marker Table

[arai-a]

In the Marker Table, currently the "Start" column shows the time from the beginning of the profile.
When comparing two profiles for the browsertime benchmark, I want to see the time from the "Navigation::Start", so that it's easier to compare two profiles (opened in two adjacent tabs) and see the difference in the timing between them.

The similar thing can be done in the Marker Chart, but the Marker Chart doesn't show the Details label for short markers, and it's hard to compare multiple events at once.

┆Issue is synchronized with this Jira Task

[arai-a]

So far, I see that getZeroAt can return possibly-non-zero value, so that the entire time becomes relative to some point.

profiler/src/selectors/profile.ts

Lines 99 to 100 in 566a17a

	export const getZeroAt: Selector<Milliseconds> = (state) =>
	getProfileRootRange(state).start;

I'm about to add an override mechanism to this.

[canova]

Hmm, currently we share the same start time for the whole profile. How would this work with multiple content processes with different Navigation::Start markers?

Also how would you correlate these marker start times with the markers in the parent process, different processes like the GPU process, or different threads in the same process?

[arai-a]

oh, I forgot to describe the plan.

I'm about to add a way to override the "zeroAt" to any point, not specific to "Navigation::Start".
The current prototype shows the following "Override zero at marker’s start" menu item for each marker,
and clicking it overrides the getZeroAt function return value to the marker's start timing.
(and the context menu will get "Reset the override for zero" menu item to reset it)

[canova]

I see, and will this context menu item change the start times of that thread/process or of the whole profile?

How can someone undo this action?

[arai-a]

to my understanding it overrides the whole profile, as I'm modifying the getZeroAt function above, which seems to be associated with the entire profile.
The "undo" can be done from the "Reset the override for zero" item, which is shown when it's overridden.

[canova]

And I assume this will change the timestamps of everything, like the sample timestmaps too? For example:

So some samples/markers are going to have negative values. I think it might be confusing for some people, especially if this will be kept in the url state (for example, assume that you get a profile link from someone else, and see negative timestamp values, I think the UI should make it obvious why it's happening, and how to undo it. Currently having this reset button in the marker context menu seems a bit unusual, since it's actually a global state at this point and not related to that marker)

(TBH, I'm not trying to be discouraging, but I think it would be good to decide on the UX of this feature and make sure that everyone is happy before implementing it. I haven't thought about it fully yet, but I will think about it and comment here more.)

[arai-a]

Thank you for your input :)

I've opened a PR in #5733 , to demonstrate how it works and how the code looks like.

And yes, it makes things before the zero to negative timestamp.

The override is done as part of the view options.
I haven't yet checked, but I suppose that doesn't persist?

Then, I agree that the "reset" should be put in different place. maybe the timeline ruler can have it?
For example, show the ruler in negative range in different color, and clicking it shows a menu with "reset" item.

[arai-a]

Moved the "reset" button to the menu buttons.
Currently the button is shown if the zeroAt is overridden, with the label "Zero at (timestamp)", and clicking it resets the override.
Maybe we could instead show a context menu on click, with "Reset" menu item.

[canova]

Ah, yeah I like this approach more. I would like to get feedback from some of our power users too though (but some of them are on PTO currently).