Why can diffsigs take sometimes really looooong?

[Uwe Geuder <jrswdnan22@snkmail.com>]

Hi!

At times I find the diffsigs command useful/educational to understand
what is going on in my build.

$ bitbake-diffsigs -t myimage do_image

Often the result is shown in no time. However, recently I got some
cases were it takes 150 (!) minutes to show a simple difference (1 line
changed in do_install of systemd).

In comparision building after that change (with sstate) takes some 10
minutes. And building everything from scratch (no sstate) takes just a
bit over 50 minutes on the same machine.

Of course the build can make good use of my 8 cores / 16 threads,
whereas diffsigs seems to run in only 1 core. Still, shouldn't every
build calculate all the dependencies, so running diffsigs should only be
a small fraction of that work?

Is there a natural explanation why diffsigs can sometimes be so slow?
Just curious to understand what is going on there.

I am on Rocko 2.4.3 if that makes a difference.


Regards,

Uwe Geuder
Neuro Event Labs Oy
Tampere, Finland
uwe.gexder@neuroeventlabs.com (Bot check: fix one obvious typo)