ginormous performance issue

[Martin Gräßlin]

Am Mittwoch 15 Juli 2009 23:06:42 schrieb Marco Martin:
> Hi all,
> talking with Alexis at akademy, we figured out something realy horrible was
> happening during the caching of plasma svgs, because when an applet is
> quickly resized, plasma cpu and disk usage spikes, actually passing all the
> time compressing images and writing them to the disk.
> so i looked a bit at it and found this
> http://websvn.kde.org/trunk/KDE/kdelibs/plasma/framesvg.cpp?r1=970932&r2=97
>5773
>
> this commit made the code cleaner, but totally defies the concept of
> delayed cache writing, in fact it writes all of the images asked to be
> inserted into the cache. why is bad?
> because if an applet is resized, every rendered svg will be inserted into
> the cache, from start size to end size of the drag resize.
> all the middle sizes are totally useless in term of the purpose of the
> cache (they won't be needed in the future) and case a tremendous cpu usage
> (valgrind, oprofile,whatever will say that 99% of the time is spent inside
> zlib, compressing the stuff to put into the hard drive, wee :))
>
> the attached patch is an horrid kludge, but kinda fixes the problem
> it removes from the pixmaps to be inserted all the ones that starts with
> the same piece of key, so all the ones with the same path, when a new
> pixmap is inserted.
> of course this is ugly, but the result is fuckingly faster...
>
> now, what could be a proper way to do it (without having to change the api,
> sigh)?
>
> a way could be like now, parsing the key and throwing away other sizes of
> the same framesvg, or just revert that commit...
> the issue is kinda urgent, because kde4.3 is affected too, so someting
> backportable should be quickly found...
that could explain why Aurorae engine is terrible slow when resizing windows. 
So please don't fix it in Theme but directly in FrameSvg as it is not only used 
in Theme.
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