[Development] Build Hotspots in the Qt build process

[Tobias Hunger]

Hi Shane,

thanks again for the presentation at FOSDEM. I really enjoyed it:-)

The list of yours seems to be ordered alphabetically. I guess that is
not necessarily the order in which we should look at the files:-) This
list is rather long and slide 36 of your presentation shows that the
files listed trigger between 90s and more than 8000s of rebuild time!
That is two orders of magnitude difference, so if we look at this we
should start by looking at those in the 8000s range:-)

Could you generate a list of files sorted by "hotness" when you get
back to your lab? Maybe the distance of the file's datapoint from the
origin would be a good measure for that? That might need some
normalizing though.

I just went over your list and have not been overly surprised with
which files are causing long rebuild times: All of them are header
files that are widely used in Qt and by Qt applications. E.g. almost
the complete set of non-private headers in qtbase/src/corelib is
listed.

There actually is one .cpp file in the list, which is rather unexpected.

Seeing the same data for Qt webkit would also be cool. That is the
part of code that feels like it is taking the longest to build in all
of Qt:-)

Best Regards,
Tobias

On Mon, Feb 3, 2014 at 10:39 PM, Shane McIntosh <mcintosh at cs.queensu.ca> wrote:
> Hi Qt developers!
>
> My name is Shane. I’m a PhD student at Queen’s University in Canada.
>
> I’ve been working on an approach for detecting build hotspots, i.e., files that not only take a long time to rebuild, but also change often. We think that these files are ideal candidates for refactoring that could shave time off of incremental builds that are really impacting software teams.
>
> We came up with an approach that I presented last weekend at FOSDEM ( slides are available here: http://www.slideshare.net/shanemcintosh/identifying-hotspots-in-software-build-process ). One of the projects that we analyzed was Qt.
>
> I bumped into Tobias at FOSDEM and he suggested that I post the list of Qt hotspots here. So, I’ve made the hotspot list available here: http://sailhome.cs.queensu.ca/~shane/content/qt_hotspots.txt
>
> I’m happy to provide a more detailed Qt dataset when I return to my lab next week.
>
> Kind regards,
> -Shane
>
> P.S.: We are conducting a survey on how build performance is impacting developers ( http://is.gd/DbMRTr ). If you could spare 5 minutes to fill out our survey, we’d really appreciate it!
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