KInit - Current state and benchmarks

[David Edmundson]

>From API.kde.org:
>Using kdeinit to launch KDE applications makes starting a typical KDE applications 2.5 times faster (100ms instead of 250ms on a P-III 500)

Certainly sounds like a good thing.

===The current State===

==Plasma==
* Apps launched from the plasma menu skip klauncher and therefore
kinit. This was done due to the API for KRun blocking somewhere
(Though I don't remember details)

This seems like something easily fixable if we tried.

* Processes launched on bootup (with the exception of kcminit,
ksmserver and kded5) skip kinit. This was due to a deadlock in
klauncher and ksmserver at the time when apps autostart moved from
frameworks.

This deadlock is since resolved in my ksmserver splitting branches.

* But Plasma apps launched from the desktop do go through klauncher
(and therefore kinit)! So we're not even consistent.

==Apps==
* The number of applications linking kinit properly under KF5 is in an
equally sorry state.
Dolphin does, but even core applications like Okular and Kate don't.

See
$ find -name 'CMakeLists.txt' -print0 | xargs -0 grep
'kf5_add_kdeinit_executable'
for a local list.

* It's also incompatible with flatpak/snaps/appimage, which is a rising trend

==Other==
Kinit is still also used for spawning KIO slaves.

===Is it still useful?===
We're not using it properly and we need to do something. Either fix it
or start to phase it out officially.

Since the time of writing kinit Qt has changed a lot. linking has
changed a bit. CPUs have changed a lot and Hard Disks have changed a
lot.

So I wrote a benchmark tool to see if the initial speed boost claim is
relevant: kde:scratch/davidedmundson/inittimer

My test does the following:
 - creates a dummy (headless) wayland server
 - spawns an app using either QProcess or sending a DBus message to KLauncher
 - times how long it takes for the first window to appear, timing the
more important real world metric and one that includes all the
factors.

Results:
(Showing the median out of 5 runs on a mid range SSD desktop)

Dolphin QProcess: 348
Dolphin Kinit: 332

KCalc   QProcess:  242
KCalc   KInit: 232

Plasmoidviewer (patched) QProces: 622
Plasmoidviewer (patched) KInit: 591

KWrite  QProcess: 391
KWrite  Kinit: 390
(unsurprisingly similar as kwrite does not have a kdeinit exec, I
included it as it shows the others aren't false positives)

===What about memory?===

Good question. It needs a similar investigation by someone who
understands memory...

===Conclusion===

My test implies there /is/ a genuine saving with kinit !
However it's far from the claimed 2.5 times faster, it is less than
1.1 times faster. Saving up to 30ms.