Comment by stick_figure

Comment by stick_figure 4 days ago

This is actually tracked at a publicly visible URL: https://commondatastorage.googleapis.com/chromium-browser-cl...

And the include graph analysis: https://commondatastorage.googleapis.com/chromium-browser-cl...

The annotated red dots correspond to the last time Chrome developers did a big push to prune the include graph to optimize build time. It was effective, but there was push back. C++ developers just want magic, they don't want to think about dependency management, and it's hard to blame them. But, at the end of the day, builds scale with sources times dependencies, and if you aren't disciplined, you can expect superlinear build times.

ahartmetz 4 days ago

Good that it's being tracked, but Jesus, these numbers!

110 CPU hours for a build. (Fortunately, it seems to be a little over half that for my CPU. "Cloud CPUs" are kinda slow.)

I picked the 5001st largest file with includes. It's zoom_view_controller.cc, 140 lines in the .cc file, size with includes: 19.5 MB.

Initially I picked the 5000th largest file with includes, but for devtools_target_ui.cc, I see a bit more legitimacy for having lots of includes. It has 384 "own" lines in he .cc file and, of course, also about 19.5 MB size with includes.

A C++20 source file including some standard library headers easily bloats to a little under 1 MB IIRC, and that's already kind of unreasonable. 20x of that is very unreasonable.

I don't think that I need to tell anyone on the Chrome team how to improve performance in software: you measure and then you grab the dumb low-hanging fruit first. From these results, it doesn't seem like anyone is working with the actual goal to improve the situation as long as the guidelines are followed on paper.

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bialpio 4 days ago

> I picked the 5001st largest file with includes. It's zoom_view_controller.cc, 140 lines in the .cc file, size with includes: 19.5 MB.
> Initially I picked the 5000th largest file with includes, but for devtools_target_ui.cc, I see a bit more legitimacy for having lots of includes. It has 384 "own" lines in he .cc file and, of course, also about 19.5 MB size with includes.
> A C++20 source file including some standard library headers easily bloats to a little under 1 MB IIRC, and that's already kind of unreasonable. 20x of that is very unreasonable.
I think you're not arguing pro-forward-declarations vs anti-forward-declarations here though - it sounds more like an argument for more granular header/source files? In .cc file, each and every include should be necessary for the file to compile (although looking at your example, bind.h seems to be unused and could be removed - looks like the file was refactored and the includes weren't cleaned up).
With that said, in the corresponding zoom_view_controller.h, the tab_interface.h include looks to be unnecessary so you did find one good example. :)

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- ahartmetz 4 days ago
  
  Yes, sure! I am arguing for whatever is necessary to reduce the total compilation cost. Pruning headers, rearranging source code to have fewer trivial modules and to reduce the size of very often included headers, even gasp sometimes using pointers just to reduce compile time! I understand that runtime performance is a very high priority for Blink, but it really doesn't matter sometimes if certain things are heap-allocated. Like things that are very expensive to instantiate anyway and that don't occur often. These will incidentally tend to have "heavy" headers, too.
  
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