plugins,caches, startup time

[Marco Martin]

Hi all,
as there is being some work in plugin caching right now, to see if /what we 
can save at startup time would be nice if different people on different 
systems do some tests.
on his system, by indexing plugins Sebas saves about 2-300 milliseconds. How 
did you test that, so that we see wether we can reproduce it on different 
systems, (may well be that on some kinds of hardware it's worth it, not on 
some other)

I did a similar test on kpackage plugin indexes, that's how all plasmoids get 
loaded, so it's quite a lot of them.

to measure the plasma startup i use
https://phabricator.kde.org/D2835
(probably not worth to push it, just easy to apply the patch with arc)
the elapsed time there is taken when the panel appears, because it's where we 
are more reasonably certain the startup is done (that would be, where/when the 
last panel appears)


to generate the plugin index, use:
kpackagetool5 --generate-index -g -t Plasma/Applet

on an ssd system i save around 5-600 milliseconds on a startup time around 5 
seconds (on a debug build of qt, which i note it matters a lot for startup 
time of qml stuff, on the same laptop a plasma session installed from neon 
packages takes less than half to start)
on an old spinning metal workstation, still debug build of qt, i save around a 
second on top of a ~10 seconds startup time

it's not much, but a considerable amount, consistent around ~10%

way more  significant, on cold caches(probably even more important, as that's 
what happens at boot time), on the slow hard drive machine, i get around 3 
seconds of difference, from around 25 seconds (yeah, pretty slow ;) to around 
22

that's done with 
echo 3 > /proc/sys/vm/drop_caches

will test on a couple more systems (on both cold/warm caches), would be nice 
to get numbers from others as well.

-- 
Marco Martin