Bug 390463

There certainly is a difference, though for me it's not as pronounced as reported.

* If I disable progress reporting in Settings, 4.0 is much faster
* But that doesn't show up in the callgrind logs, where 3.3 is mostly busy in the filter itself, 4.0 seems to be mostly busy in the lod and multithreading mechanism.

Created attachment 110682 [details]
Callgrind logs

Started callgrind the moment the image was fully loaded. Opened the gradient map filter, selected another gradient, waited until the preview was done, then press ok. When the image was updated, callgrind was disabled and a dump made.

Thanks for checking. 
But disabling progress reporting doesn't seem to make any noticeable difference here. It takes almost exact same amount of time to process same image.

Yes, Color to Alpha filter is extremely slow here. And disabling progress reporting doesn't help (which disables only reporting in the statusbar only, not in the layers docker). The bug is seen much better when instant preview is disabled.

I always thought this issue was related to https://bugs.kde.org/show_bug.cgi?id=372221 thinking it was a side effect of using the new color selector, a least I've been experiencing this delay since, filters like color to alpha where instantaneous previously, as for now it takes close to a minute to produce the effect.

No, it's completely unrelated.

Git commit 907f88b9445e32425ddf384e4c99815b853bf680 by Dmitry Kazakov.
Committed on 01/03/2018 at 15:07.
Pushed by dkazakov into branch 'master'.

Fix filters slowdown due to progress reporting

Now we have a special type of a sequential iterator
(KisSequentialIteratorProgress), which can also handle
progress reporting (report on every new line).

This patch also refactors a few filters to use sequential
iterator and support multithreading/instant preview.

A  +55   -0    libs/image/KisSequentialIteratorProgress.h     [License: GPL (v2+)]
M  +3    -10   libs/image/filter/kis_color_transformation_filter.cc
M  +11   -0    libs/image/filter/kis_filter.cc
M  +2    -9    libs/image/kis_gradient_painter.cc
M  +1    -10   libs/image/kis_lod_transform.h
M  +5    -2    libs/image/kis_progress_update_helper.h
M  +31   -2    libs/image/kis_sequential_iterator.h
M  +5    -4    libs/image/krita_utils.cpp
M  +41   -0    libs/image/tests/kis_iterators_ng_test.cpp
M  +2    -0    libs/image/tests/kis_iterators_ng_test.h
M  +7    -4    libs/widgetutils/KoUpdater.cpp
M  +10   -13   plugins/filters/colors/kis_color_to_alpha.cpp
M  +4    -13   plugins/filters/colors/kis_minmax_filters.cpp
M  +3    -9    plugins/filters/colorsfilters/colorsfilters.cpp
M  +3    -7    plugins/filters/embossfilter/kis_emboss_filter.cpp
M  +33   -36   plugins/filters/fastcolortransfer/fastcolortransfer.cpp
M  +2    -9    plugins/filters/gradientmap/krita_filter_gradient_map.cpp
M  +11   -28   plugins/filters/imageenhancement/kis_simple_noise_reducer.cpp
M  +18   -21   plugins/filters/imageenhancement/kis_wavelet_noise_reduction.cpp
M  +7    -13   plugins/filters/noisefilter/noisefilter.cpp
M  +9    -26   plugins/filters/oilpaintfilter/kis_oilpaint_filter.cpp
M  +1    -1    plugins/filters/oilpaintfilter/kis_oilpaint_filter.h
M  +63   -43   plugins/filters/pixelizefilter/kis_pixelize_filter.cpp
M  +3    -0    plugins/filters/pixelizefilter/kis_pixelize_filter.h
M  +12   -18   plugins/filters/raindropsfilter/kis_raindrops_filter.cpp
M  +7    -7    plugins/filters/randompickfilter/randompickfilter.cpp
M  +1    -0    plugins/filters/randompickfilter/randompickfilter.h
M  +65   -49   plugins/filters/roundcorners/kis_round_corners_filter.cpp
M  +4    -11   plugins/filters/threshold/threshold.cpp
M  +46   -57   plugins/filters/unsharp/kis_unsharp_filter.cpp
M  +2    -2    plugins/filters/unsharp/kis_unsharp_filter.h
M  +3    -6    plugins/filters/wavefilter/wavefilter.cpp

https://commits.kde.org/krita/907f88b9445e32425ddf384e4c99815b853bf680