spans linked by flow_ids render poorly with nesting about perfetto HOT 11 OPEN

Simple case with flow IDs set
sequence_test.proto.zip

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Hey @lednakashim,

Thanks for raising the bug, I can see the issue.

I can imagine two ways to address this:

• Detect the parent child relationship and draw a different style of arrow (i.e. a vertical arrow).
• Try to prevent arrows from going backwards as much as possible by sliding the ends forward or backward while keeping them within the bounds of their slices.

While the former would need some investiagtaion, the latter would be quite trivial and I think would acheive the desired effect - something like in the screenshot.

Let me know what you think.

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Preference for down arrow as the parent span is ran "simultaneously" with the child span.

The second version (what is drawn) is a bit ambiguous as it is not clear what the arrow start is used to denote. Control flow switches from the parent to the child at edge rather than some time before the edge.

Realistically either solutions work

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The second version (what is drawn) is a bit ambiguous as it is not clear what the arrow start is used to denote.

Agreed. The difficulty is, the arrow has to begin somewhere, and unless it's at one of the ends of the slice I think it could be misinterpreted as significant.

Ideally the tool would connect parents to children via a down arrow

Could you sketch out what you had in mind re "down arrow"?

A few suggestions:

Name	Screenshot
No circle
Align start with destination slice
Start down
Straight down
Aligned start with start of source slice
Reversed (makes more sense when zoomed out)

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Wow, these are neat:

I was initially thinking that a connection from the center make sense but one of the variants you have is more elegant

Perhaps
Aligned start with start of source slice
because the meaning of the arrow control points are clear and they doesn't duplicate the meaning of the edge

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For fun here is another synthetic sequence typical of pipelined producer-consumer queues
sequence_test.proto.zip

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Thanks for the example trace :)

OK here's my latest thinking. You can try the result out here - just make sure to enable the "Neater Flow Arrows" flag.

Let me know what you think.

Edit: Fixed URL.

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Actually I think having arrows emenating from the left of the parent slice when there isn't much room makes a bit more sense - Link

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Actually I think having arrows emenating from the left of the parent slice when there isn't much room makes a bit more sense - Link

I've been using this branch for few weeks and it seams to help a lot. You guys going to merge it?

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there is an adjacent issue where the time calculation of nested flow seems to be always nailed to 0 which is maybe additionally worth filing

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Hey sorry for the delay, I haven't had a lot of time to work on this recently.

We just landed a patch (on autopush channel) which does a much better job of working out slice ancestors under the hood and draws arrows from the start of the parent slice which looks like this:

If this is enough, please close the issue. Otherwise I'll rebase my changes on top of this CL and try and get some opinions from the team.

there is an adjacent issue where the time calculation of nested flow seems to be always nailed to 0 which is maybe additionally worth filing

Can you expand on this a little, maybe attach a screenshot?

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