Review Request: KImageCache optimization

[Mark Gaiser]

> On Feb. 23, 2012, 6:33 p.m., Milian Wolff wrote:
> > given that you have unit tests at hand, why not write a benchmark to get proper before/after numbers that show the impact of this patch?

Right.. That's not exactly easy to "just" do since i would have to read a dir with images, insert it in the cache and read it back from the cache. So not going to do that. What i did do is change the size to "SizeEnormous" so the icon is a bit bigger (128x128) and just let QBENCHMARK do it's thing with insert(write) and find(read). The results are as follows:

-- Before patch --
READ : 0.019 msecs per iteration (total: 79, iterations: 4096)
WRITE: 0.010 msecs per iteration (total: 88, iterations: 8192)

-- After patch --
READ : 0.019 msecs per iteration (total: 79, iterations: 4096)
WRITE: 0.0026 msecs per iteration (total: 87, iterations: 32768)

Reading is equal in speed, writing is ~5x faster after the patch.


- Mark


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On Feb. 23, 2012, 6:21 p.m., Mark Gaiser wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/104052/
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> 
> (Updated Feb. 23, 2012, 6:21 p.m.)
> 
> 
> Review request for kdelibs, David Faure and Michael Pyne.
> 
> 
> Description
> -------
> 
> I was running KWin through callgrind to see where possible bottlenecks are. I wasn't expecting much since it improved greatly during the 4.8 dev cycle, however one stood out. The saving of PNG images was taking about 1/5th of the time in KWin that i could see directly. That looked like something i might be able to optimize.
> 
> What this patch is doing is storing the actual image bits to prevent saving a PNG image to the mmapped cache. That was a hot code path in time (cycles), not even in calls. I've also reduced the amount of memory copies to a bare minimum by adding a rawFind function to KSharedDataCache which fills a QByteArray::fromRawData thus preventing a expensive memory copy. The rawFind is used for looking up an image and fetching it's data without copying it. That is done because QImage seems to make a copy itself internally. I don't have any performance measurements, however, prior to this patch my kwin test was using up ~5.000.000.000 cycles. After this patch it's using up 1.370.000.000. I don't have raw performance numbers to see if the cache itself is actually faster, it certainly has become a lot cheaper to use the cache. Logic wise i would say creating a QImage from the cached data should be way faster now since there is no step involved anymore in decoding the image. Storing is certainly an order of magnitude faster.
> 
> Special thanks go to David Faure for helping me a great deal with this.
> 
> 
> Diffs
> -----
> 
>   kdecore/util/kshareddatacache.h 339cecc 
>   kdecore/util/kshareddatacache.cpp 9fe3995 
>   kdeui/tests/CMakeLists.txt 63788f6 
>   kdeui/tests/kimagecachetests.h PRE-CREATION 
>   kdeui/tests/kimagecachetests.cpp PRE-CREATION 
>   kdeui/util/kimagecache.cpp a5bbbe1 
> 
> Diff: http://git.reviewboard.kde.org/r/104052/diff/
> 
> 
> Testing
> -------
> 
> I've also written a bunch of test cases (greatly improved by David Faure) to see if i didn't break anything. According to the test (which is also comparing the actual image bits) it's all passing just fine.
> 
> 
> Thanks,
> 
> Mark Gaiser
> 
>

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