Long tasks in the report

We want to show more information about long tasks, in order to help reduce TTI/TBT.

First: a new “long tasks” diagnostic audit. We’ve been talking about this. Idea is to show the 5 longest tasks.

Quick way to preview the long tasks–in bootup-time.js:

console.log([...tasks].sort((a, b) => b.duration - a.duration).filter(t => t.duration >= 50));

• We know the start and end times of each task. Instead of a table, should we explore a timeline visualization, perhaps also adding when TTI/FCP/LCP is?
• Should we show more than 5? Maybe not all–The verge has ~60 long tasks. 20?
• What is “Other”? It is different from “unattributable”, yes? Should we filter out these two from this audit?

Second: (new idea, please discuss) augment bootup-time with long tasks

We could add subrows for each script, listing the top n long script tasks.

[paulirish]

Quick way to preview the long tasks–in bootup-time.js:

Nice. I extended that a tad more:

    const longtasks = [...tasks].sort((a, b) => b.duration - a.duration).filter(t => t.duration >= 50 && t.unbounded === false);

    const also = longtasks.map(t => ({
      url: BootupTime.getAttributableURLForTask(t, jsURLs),
      group: t.group.label,
      start: t.startTime,
      self: t.selfTime,
      duration: t.duration
    }));
    console.table(also);

Instead of a table, should we explore a timeline visualization,

we can, but let’s start with the table. the timeline viz scope can get big really quick so i wanna make sure we ship some basic ground truth and then augment from there.

Should we show more than 5?

good call. up to 20-ish sg.

What is “Other”? It is different from “unattributable”, yes? Should we filter out these two from this audit?

different yes. seems like Other happens when most of the time is attributed to events like these. (which seems weird as they are fired at the toplevel/scheduler-level.)

i don’t think we should filter either out as Other/Unattributable can still mess up your FID/TBT/TTI

Second: augment bootup-time with long tasks

yeah seems pretty reasonable.

[patrickhulce]

Unattributable just means we couldn’t get a stack that resolved to any script. This should be attributable once a PR for #8526 lands which I’m free to work on now 😃