How to do performance debugging?

[mavam]

I'm trying to understand why my application runs so incredibly slow. I did some stack sampling but don't get quite far:

(This is speedscope and here's the sample.)

I'm looking at potentially really large tables, like this one:

I think the functional reactive UI makes it hard to narrow this down to a root cause. I have several hunches, of course, but I cannot validate them one-by-one efficiently. For example, the columns (with potentially 10k elements each) are being added like this:

        Elements body;
        body.reserve(slice.rows());
        for (size_t row = 0; row < slice.rows(); ++row) {
          auto cell = StaticCell(slice.at(row, col), state_->theme);
          body.push_back(std::move(cell));
        }
        body_->Add(lift(vbox(std::move(body))));

I can only guess that this is somewhere visible on the flame graph.

How do you do performance debugging?

[ArthurSonzogni]

It looks like it spent time trying to determine the size of string.
Could you check if #691 fixed the issue?

Then I would try to limit the amount of lines rendered inside the table. Most of it won't be shown, so there are no need to do the layout for 10k elements.
I see you took a slice, so that's probably what you are already doing.

[ArthurSonzogni]

Are you sure? I can't reproduce.

Could you try again? What file is failing to compile? I don't have any case Left: occurrence in my library.
I don't see any API breakage when comparing v4.2 vs v4.1.1

[mavam]

The Left error comes up from a small helper function where I have using enum Direction. The full qualified token would be Direction::Left. The type Direction was introduced with #583, which is not part of the support branch.

So while this might not be a breaking change but an enhancement, I had to refactor my application to work with main.

Could it make sense to cut a 5.0-rc1 and label that as pre-release explicitly?

[ArthurSonzogni]

I see! So you don't need a minor release from v4.1.1, but a major release.

I would like to merge the few pending PR we have.
Let's say in a week for a v5.0 ?

[ArthurSonzogni]

I see! So you don't need a minor release from v4.1.1, but a major release.

I would like to merge the few pending PR we have. One improves screen drawing benchmark by 20%.

Let's say in a week for a v5.0 ?

[mavam]

That works great timing-wise, looking forward to it!