we are now in kde 4.3 beta and qt 4.5.1

but their performance (with proper display drivers installed and composite effects disabled) on a normal computer (pentium 4 / celeron 4) is way slower than of kde 3.5

try stuff like :

scroll a website in konqueror

switch tabs in konqueror

use 'rectangle selection' in a folder with icons and play with the selection across th window

resize the drawing area in paint

try also to add the cpu meter plasmoid on the panel and watch it when working on the computer. youll notice that everytime you do some interactions in a sequence cpu screams his head off in panic (unlike kde 3 that 'takes stuff easy')

the causes i can think of are

in kde - various effects across the system are 'hard wired' into kde and cannot be disabled. mainly non-composite visual effects (fading and stretching stuff / smooth scroling etc)

in qt - stuff being implemented less efficient than qt 3 (too much redrawing etc)

in either one of them - too much redawing etc (perhaps stuff like trying to draw every single frame instead of 'efficient' amount of frames in dragging / scrolling etc)

i want to ask what other causes for the bad performance there are and what is / can be done to get kde 4 to perform same or better than kde 3 on any computer (as claimed several times during the early releases of kde 4)

Which Style do you have specified in System Settings > Appearance > Style? Oxygen is apparently not very efficient.

Plastik

I'm not 100 % sure about this (actually, not even 50 % sure), but you could try to disable dri (in xorg.conf) to see if it speeds things up. As far as I know, Qt4 uses direct rendering by default. If DRI is implemented by a software fallback (e.g. mesa), it could get quite slow.

Once again, I don't know if this is correct or not. If you're not sure about how to enable dri again without GUI, wait until someone's confirmed that it's safe to disable it.

its not the VERY bad performance caused by faulty xorg - but 'just bad' performance (and just higher cpu load) when compared to kde 3

the checklist in the beginning is the kind of places where the bad performance stands out the most

i am sure its not dri related but something 'inside' kde or qt themself

i can try without dri later. for now - i allready tried with the vesa driver and it did not improve performance

I've tried some of the things the OP mentioned, and can reproduce none of them. However, I believe I know what the cause is. E.g. running KDE4 on top of a stock MEPIS installation gives me some bed graphics performance, like e.g. scrolling is very slow. It has to do with the way Xorg and Intel video interact. Moving to Xorg from unstable solves the issue.

If you happen to use Kubuntu 9.01, there is a known issue as well with intel video drivers and the 2.6.29 kernel. I installed a 2.6.29 kernel on MEPIS for fun, and indeed, it almost kills the performance.

What I am trying to say is that many issues are very likely not caused by KDE, but by underlying components. KDE4 uses some features that were simply not required by KDE3, and therefore did not affect KDE3.

this happens to me on arch linux on all my boxes (pentium 3 and 4s with 256 - 512 ram)

they have intel sis nvidia 3dfx video cards

it happens with xorg 1.4 1.5 1.6

a friend of mine confirmed this on debian too

this is likely to be so on all lightweight distros (not ubuntu mandriva etc) where the slowness of the entire os does not hide the slowness of kde

to reproduce

get pentium 4 below 2 ghz with 512 m ram (pentium 3 to feel the difference more clearly)

install some lightweight distro

install kde 3.5 and use for a while to get used to its speed

install kde 4 and try again

confirmed - same performance with dri disabled

My experience is that Arch does not perform significantly faster than e.g. Debian (or MEPIS). So I doubt if it is a case of 'hiding performance issues due to overall slowness'.

I think I am quite aware of how KDE3 performs compared to KDE4, since I use both. KDE3 is more lightweight when it comes to Xorg memory consumption, that is a fact. But I find KDE4 to be more snappy in overall use. Especially with desktop effects enabled, there is no more 'window tearing'. The menu (Lancelot) opens faster, krunner is more responsive, and so is ksysguard (ctrl-esc). So I do not recognize a huge performance difference.

I use machines with a minimum of 1 GB: 2 laptops with dual core intel CPU and one desktop with a single core AMD64. All three run MEPIS, either with KDE3 or KDE4.

debian mepis arch are all lightweight distros. i consider heavy distros kubuntu etc

the case here is pentium 4 512 m ram and intel display chipset / display chipsets without dri support (and all boxes with lower specs on which kde 3 runs with good performance)

if kde 4 is written efficiently than it gotta have same (or better) performance than kde 3 - but it does not (in the same conditions - same task + composite diabled + similar widget style)

where the cause is and what can be done to fix it

You could try running valgrind ( both cachegrind and memcheck ) over some of the more memory using processes ( use top and xrestop to find the appsin question ) to discover where efficiency improvements are needed then report this to the developers.

bcooksley wrote:You could try running valgrind ( both cachegrind and memcheck ) over some of the more memory using processes ( use top and xrestop to find the appsin question ) to discover where efficiency improvements are needed then report this to the developers.

I too have similar CPU loads as the OP. But I've found that the biggest CPU/RAM user is nsplugin.
I advice OP to install htop if he hasn't already and montor the processes that use a lot of CPU / RAM.
I've noticed that both KWin and Plasma tend to use a lot of resources when used for a longer period of time.
That's why I have this alias in bashrc:

Code: Select all

alias resetkwin='kquitapp kwin && kwin&'
alias resetplasma='kquitapp plasma && plasma&'
alias killplasma='kquitapp plasma'


But reset plasma doesn't work...
Anyway hope that helps.

Try the following

Code: Select all

kquitapp plasma && sleep 10s && plasma &

Note that if you are running KDE 4.3, then it is plasma-desktop instead of plasma.

bcooksley wrote:Try the following

Code: Select all

kquitapp plasma && sleep 10s && plasma &

Note that if you are running KDE 4.3, then it is plasma-desktop instead of plasma.

That worked! Thanks.


Does anyone know why KWin, Plasma or nspluginviewer would use up to 68% (KWIn and nspluginviewer mostly)CPU??

NSPluginViewer is probably Flash, which I disabled for virtually all sites except Youtube, but it still starts anyway.
No idea why KWin does ( which compositing effects do you have enabled? )