Re: [Kdiff3-user] kdiff3 consumes 100% cpu, seems hung

[Maurice v. d. P. <gri...@kf...>]

On Mon, Jan 05, 2015 at 06:15:06PM +0100, Joachim Eibl wrote:
>    I suppose this is an effect of KDiff3-0.9.98 trying to analyze line
>    lengths for variable width fonts, where each character has to be analyzed.
>    If KDiff3 becomes responsive again after a long wait and only for long
>    files then that is the reason.

Looking at the callgrind output the time is being spent in 1.9M calls of
QFontEngineFT::loadGlyph (for reference, on my machine that function is
only called 358 times).

There are cases where this function is called while
DiffTextWindow::prepareTextLayout is on the call stack, but I find it hard
to tell why the loadGlyph function would be called so often.
prepareTextLayout is called 32K times in his profile and 31K times in
mine.

#0  QFontEngineFT::loadGlyph (this=this@entry=0x1158040, set=set@entry=0x1158128, glyph=2, subPixelPosition=subPixelPosition@entry=..., format=format@entry=QFontEngine::Format_None, fetchMetricsOnly=fetchMetricsOnly@entry=true)
    at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qfontengine_ft.cpp:816
#1  0x00007ffff75fbf03 in loadGlyph (fetchMetricsOnly=true, format=QFontEngine::Format_None, subPixelPosition=..., glyph=<optimized out>, this=0x1158040) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qfontengine_ft_p.h:281
#2  QFontEngineFT::recalcAdvances (this=0x1158040, glyphs=0x7fffffffac98, flags=...) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qfontengine_ft.cpp:1611
#3  0x00007ffff7528052 in hb_getAdvances (font=<optimized out>, glyphs=0x115f320, numGlyphs=61, advances=0x115f4a0, flags=<optimized out>) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qfontengine.cpp:105
#4  0x00007ffff6d4b0f6 in HB_HeuristicPosition (item=item@entry=0x7fffffffb030) at /var/tmp/portage/dev-qt/qtcore-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp:441
#5  0x00007ffff6d4cfff in HB_BasicShape (shaper_item=0x7fffffffb030) at /var/tmp/portage/dev-qt/qtcore-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp:624
#6  0x00007ffff6d51c03 in HB_ShapeItem (shaper_item=0x7fffffffb030) at /var/tmp/portage/dev-qt/qtcore-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp:1419
#7  0x00007ffff7559b20 in QTextEngine::shapeTextWithHarfbuzz (this=this@entry=0x115d270, item=item@entry=0) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qtextengine.cpp:1342
#8  0x00007ffff755a4b2 in QTextEngine::shapeText (this=this@entry=0x115d270, item=item@entry=0) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qtextengine.cpp:935
#9  0x00007ffff755a7d5 in QTextEngine::shape (this=this@entry=0x115d270, item=item@entry=0) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qtextengine.cpp:1450
#10 0x00007ffff756bbaf in QTextLine::layout_helper (this=this@entry=0x7fffffffb970, maxGlyphs=maxGlyphs@entry=2147483647) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qtextlayout.cpp:1761
#11 0x00007ffff756cb9e in QTextLine::setNumColumns (this=this@entry=0x7fffffffb970, numColumns=numColumns@entry=2147483647) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qtextlayout.cpp:1550
#12 0x00007ffff756cc05 in QTextLayout::endLayout (this=0x7fffffffba90) at /var/tmp/portage/dev-qt/qtgui-4.8.6-r1/work/qt-everywhere-opensource-src-4.8.6/src/gui/text/qtextlayout.cpp:644
#13 0x0000000000431235 in DiffTextWindowData::prepareTextLayout (this=0x1115380, textLayout=..., visibleTextWidth=-1) at difftextwindow.cpp:870
#14 0x000000000042ee37 in DiffTextWindow::getMaxTextWidth (this=0x110f0d0) at difftextwindow.cpp:341
#15 0x0000000000476f8c in KDiff3App::setHScrollBarRange (this=0x8450b0) at pdiff.cpp:428
#16 0x000000000047733a in KDiff3App::resizeDiffTextWindowHeight (this=0x8450b0, newHeight=57) at pdiff.cpp:471

What do you think?

Regards,
Maurice.

-- 
Maurice van der Pot

Kdiff3 developer   gri...@kf...   http://kdiff3.sourceforge.net