Review Request 111050: Fast mime detection speedup.

[Mark Gaiser]

> On June 24, 2013, 9:19 a.m., David Faure wrote:
> > kdecore/services/kmimetype.cpp, line 316
> > <http://git.reviewboard.kde.org/r/111050/diff/3/?file=165328#file165328line316>
> >
> >     I can't review this. It completely forks an existing method (findByUrlHelper), which is already supposed to have a fast path (not reading the contents of the file). So why not improve the existing method, rather than fork it? With this patch, I can't see what you changed compared to the original method, and what might possibly be missing (= regression).

Right, a very valid case. However considering the speedup has dropped down to just ~2x... and given the possibility's of possible regressions in dead code. I'm not keen on making a new patch.

If you think it's worth, I'll make a new one. If you think it's not then I'll discard this reviewrequest.


> On June 24, 2013, 9:19 a.m., David Faure wrote:
> > kdecore/services/kmimetyperepository.cpp, line 594
> > <http://git.reviewboard.kde.org/r/111050/diff/3/?file=165329#file165329line594>
> >
> >     This can't possibly be a speedup :-)
> >     
> >     In fact I don't see what the parsing of the globs file has to do with checking that the essential mimetypes exist (they typically don't have globs, even).

A leftover from previous patch versions.


- Mark


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On June 23, 2013, 9:21 p.m., Mark Gaiser wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/111050/
> -----------------------------------------------------------
> 
> (Updated June 23, 2013, 9:21 p.m.)
> 
> 
> Review request for kdelibs, David Faure and Frank Reininghaus.
> 
> 
> Description
> -------
> 
> Hi,
> 
> I've recently seen Frank Reininghaus do his best in speeding up the rendering in dolphin with regards to the app icons. And trying to prevent icon flickering between "unknown" and the actual icon.
> 
> While reading his posts on the mailing list i was beginning to wonder: "is fast mime detection actually fast"? While it was certainly faster then "slow" mime detection, it still didn't really seem fast to me. A small benchmark app hat ran fast mime detection in /usr/bin took ~40ms to complete. That's for just 2656 items.
> 
> After quite a bit of profiling i managed to to bring the duration down from ~40ms to ~3ms sometimes ~4ms. That's well over 10x faster.
> Mime detection by extension (like "file.tar.bz") is done as follows:
> 
> file.tar.bz
> Loop - find first dot
> - "tar.gz"
> if that matches a mime type then it's returned if it doesn't then it proceeds on to the next dot:
> - next dot: "gz"
> if that matches.. return.
> Otherwise it will return the default mime type.
> 
> I am getting an inconsistency. Using the unpatched fast mime detection on a file like: "test.tar.gz" gets detected as "application-x-compressed-tar" where the patched version detects it as "application-gzip". The slow and detailed mime detection detects the same file as "application-x-compressed-tar". What should it be? application-gzip or application-x-compressed-tar?
> 
> Note: This improved detection does expect folders to end with a "/". Otherwise they will be detected as application-octet-stream (the default). But i think this is common sense to let folders end with a "/". If any apps that don't do that, they should fix it i suppose.
> 
> Best thing, it's all internal and private api change. No public function is changed.
> 
> All feedback is welcome! If possible, i would like to put this in KDE 4.11.
> 
> 
> Diffs
> -----
> 
>   kdecore/services/kmimetype.h bc35bcf 
>   kdecore/services/kmimetype.cpp d748523 
>   kdecore/services/kmimetyperepository.cpp f56f48e 
> 
> Diff: http://git.reviewboard.kde.org/r/111050/diff/
> 
> 
> Testing
> -------
> 
> Tested this using just output comparison between the old version and the new implementation. It works just fine.
> kurlmimetest output:
> ********* Start testing of KUrlMimeTest *********
> Config: Using QTest library 4.8.4, Qt 4.8.4
> PASS   : KUrlMimeTest::initTestCase()
> PASS   : KUrlMimeTest::testURLList()
> PASS   : KUrlMimeTest::testOneURL()
> PASS   : KUrlMimeTest::testFromQUrl()
> PASS   : KUrlMimeTest::testMostLocalUrlList()
> PASS   : KUrlMimeTest::cleanupTestCase()
> Totals: 6 passed, 0 failed, 0 skipped
> ********* Finished testing of KUrlMimeTest *********
> 
> 
> Thanks,
> 
> Mark Gaiser
> 
>

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