One of my biggest frustrations in profiling startup performance
has been the fact that exactly which code runs during before or
after first paint changes based on arbitrary timing factors. If
I make a 5ms improvement to one section of code, a 100ms chunk
of code winds up running after first paint rather than before.
If I make a 5ms improvement to another section of code, a 150ms
chunk of code winds up running *before* first paint rather than
after. This also shows up in the ts_paint timings on talos,
where we have a fairly consistent cluster of high times, a
fairly consistent cluster of low times, and very little
in-between.
Presumably, if we're OK with these chunks *ever* running after
first paint, then they should always run after first paint. And
vice versa.
I've made various attempts to get a handle on this, but never
with much success. The last time, I got as far as fixing the
broken TaskTracer build before I finally gave up trying to find
a useful way to analyze the data. What I'd really like is a
handle on what tasks are run, when, who schedule them (and
when), and what code they run.
After that, I'd ideally like to find a way to run async tasks
during startup so that I'm guaranteed which parts run before
first paint and which run after.
Has anyone else made any progress on this front? Are there any
other tools that I'm overlooking? Is there a sensible path
forward?
Thanks.
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