[Development] QTBUG-43096 - QML instantiation performance decadence

[Tomasz Olszak]

Hi Uwe,

I quickly reviewed QSkinny and it really nicely exposes C++ to Qml. I can't
see however, how you made e.g. QskVariant::stops readable from Qml. Writing
stops is possible due to QMetaType::registerConvertes, but how you can
iterate overs stop from Qml?

Thanks in advance for clarification,
Tomek

PS: I also tried to have the same implementation for C++ and Qt Qml and now
some classes contains duplicated getters/setters (QVariantList instead of
QVector<C++Type>).

2018-05-31 9:48 GMT+02:00 Chris Adams <chris.adams at qinetic.com.au>:

> On Thu, May 31, 2018 at 5:21 PM, Uwe Rathmann <Uwe.Rathmann at tigertal.de>
> wrote:
> > Hi Simon,
> >
> >> I ran benchmarks comparing a release build of 5.12 against 5.1.1 and ran
> >> the benchmark mentioned in the task, where Qt 5.12 came out in average
> >> faster by a factor of 4.
> >
> > Christophers comment in the JIRA ticket raises some questions concerning
> > the correctness of those benchmarks.
> >
> > Would you be so kind to clarify how far we can trust in these numbers ?
>
> I did have a couple of questions about that particular benchmark
> result, but that doesn't mean that the conclusion is incorrect.
>
> It's important to note that the issue may lie in the original numbers,
> as the library metrics test previously used some hand-rolled methods
> to discard outliers and perform an average, and worked on wall time
> rather than cpu ticks - a method which may very well have been wrong
> (and that would be entirely my fault).
>
> Also, it is worth pointing out that recently a considerable effort has
> been made to improve the benchmarking of all stages of QtQuick
> applications (from the JS side of things, to the QML compiler side of
> things, to the scene graph side of things), as the grafana and
> qmlbench etc tracking proves.  Performance regressions are now being
> caught, and performance metrics are easily visible, thanks to those
> efforts, and that is definitely have a very positive effect on
> performance outcomes for everyone.
>
> FWIW I am certain that the QML engine in Qt 5.12 will indeed perform
> better than it did in Qt 5.1 days (or any other version of Qt) because
> the people working most closely with the engine and the people working
> most closely with QtQuick both believe it to be so, and I trust their
> judgement.
>
> Best regards,
> Chris.
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