Review Request: Implemented multithreading in KFileItemModelSortAlgorithm

[Frank Reininghaus]

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Thanks for the new patch, looks good! I've added a few comments below which will might make the code less complex.

Can you provide some benchmarks (i.e., sorting time for a fixed number of items with the current single-threaded implementation and for 2 and 4 threads)?


dolphin/src/kitemviews/private/kfileitemmodelsortalgorithm.cpp
<http://git.reviewboard.kde.org/r/107025/#comment16466>

    I would not do any checks here - just determine numberOfThreads and call parallelSort().
    
    Right now, some parts are needlessly duplicated, like the "span < 2" check.
    
    I think that even the "span > 100" check is better moved to parallelSort() - consider the case that the sort interval is split a couple of times and gets very small - we want to fall back to sequentialSort() also in that case.



dolphin/src/kitemviews/private/kfileitemmodelsortalgorithm.cpp
<http://git.reviewboard.kde.org/r/107025/#comment16467>

    I'd change that to
    
    if (numberOfThreads > 1 && span > 100)
    
    (or whatever threshold makes sense). You can also remove the "span < 2" check above then.



dolphin/src/kitemviews/private/kfileitemmodelsortalgorithm.cpp
<http://git.reviewboard.kde.org/r/107025/#comment16468>

    Better only write 'else' here. numberOfThreads is guaranteed to be 1 if it's not larger than 1, so why check it? Right now, it looks at first sight like we could even return from that function without getting any sorting done at all ;-)


- Frank Reininghaus


On Oct. 25, 2012, 2:14 p.m., Emmanuel Pescosta wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/107025/
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> (Updated Oct. 25, 2012, 2:14 p.m.)
> 
> 
> Review request for Dolphin and Frank Reininghaus.
> 
> 
> Description
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> Implemented multithreading in KFileItemModelSortAlgorithm.
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> If more than 100 items to sort and ideal thread count is greater than 1 -> sort them with parallelSort (2 Threads)
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> Use maximal 2 Threads, because more than 2 Threads are "slower" (more overhead than speed up). (I also have a patch which uses n Threads for sorting, if you want test it ;)
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> 
> Diffs
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>   dolphin/src/kitemviews/private/kfileitemmodelsortalgorithm.h 3a596df 
>   dolphin/src/kitemviews/private/kfileitemmodelsortalgorithm.cpp e0aac13 
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> Diff: http://git.reviewboard.kde.org/r/107025/diff/
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> 
> Testing
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> About 2 seconds faster with sorting 500.000 files.
> About 5 seconds faster with sorting 1.000.000 files.
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> 
> Thanks,
> 
> Emmanuel Pescosta
> 
>

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