[Development] Item creation time in QML

[Rutledge Shawn]

On 9 Feb 2015, at 11:25, Gunnar Sletta <gunnar at sletta.org> wrote:

> Hi,
> 
> Thought I would share a couple of benchmark numbers for item creation time in QML. The sources are found here: https://github.com/sletta/stuff/tree/master/qml/benchmarks. The motivation is that we can generally animate a large number of items, but we often stutter when adding and removing stuff from the scene or when scrolling complex lists.
> 
> How the benchmark works is that the it tries to figure out how many operations of a given type is possible each frame (not per second) while sustaining a perfect 60 fps (or whatever other fps you target). For these numbers, we’re looking at delegation creation and destruction. You can look at the content of each specific benchmark here: https://github.com/sletta/stuff/tree/master/qml/benchmarks/benchmark/creation. 
> 
> This was measured on my 13” MacBookPro, Intel i5 2.6Ghz, Intel Iris GPU using ‘dev’. On lower end mobile and embedded, the numbers can be an order of magnitude lower. 
> 
> > ./qmlbench --delay 2500 --repeat 5 --fullscreen --fps-interval 2000  benchmark/creation
> running: "benchmark/creation/delegates_blendedrect.qml"
>      485 ops/frame
>      490 ops/frame
>      487 ops/frame
>      477 ops/frame
>      489 ops/frame
>      485.6 ops/frame average
> running: "benchmark/creation/delegates_buttoncontrol.qml"
>      10 ops/frame
>      10 ops/frame
>      10 ops/frame
>      10 ops/frame
>      10 ops/frame
>      10 ops/frame average
> running: "benchmark/creation/delegates_complex.qml"
>      11 ops/frame
>      11 ops/frame
>      11 ops/frame
>      11 ops/frame
>      11 ops/frame
>      11 ops/frame average
> running: "benchmark/creation/delegates_image.qml"
>      303 ops/frame
>      304 ops/frame
>      301 ops/frame
>      304 ops/frame
>      304 ops/frame
>      303.2 ops/frame average
> running: "benchmark/creation/delegates_labelcontrol.qml"
>      81 ops/frame
>      81 ops/frame
>      80 ops/frame
>      81 ops/frame
>      82 ops/frame
>      81 ops/frame average
> running: "benchmark/creation/delegates_longtext.qml"
>      37 ops/frame
>      37 ops/frame
>      37 ops/frame
>      37 ops/frame
>      37 ops/frame
>      37 ops/frame average
> running: "benchmark/creation/delegates_rect.qml"
>      527 ops/frame
>      530 ops/frame
>      527 ops/frame
>      526 ops/frame
>      531 ops/frame
>      528.2 ops/frame average
> running: "benchmark/creation/delegates_script.qml"
>      382 ops/frame
>      387 ops/frame
>      387 ops/frame
>      374 ops/frame
>      385 ops/frame
>      383 ops/frame average
> running: "benchmark/creation/delegates_text.qml"
>      128 ops/frame
>      128 ops/frame
>      127 ops/frame
>      128 ops/frame
>      127 ops/frame
>      127.6 ops/frame average
> running: "benchmark/creation/delegates_text_nativerendering.qml"
>      138 ops/frame
>      137 ops/frame
>      136 ops/frame
>      137 ops/frame
>      136 ops/frame
>      136.8 ops/frame average
> running: "benchmark/creation/delegates_text_plain.qml"
>      130 ops/frame
>      129 ops/frame
>      128 ops/frame
>      128 ops/frame
>      129 ops/frame
>      128.8 ops/frame average
> running: "benchmark/creation/delegates_text_richtext.qml"
>      46 ops/frame
>      46 ops/frame
>      46 ops/frame
>      46 ops/frame
>      46 ops/frame
>      46 ops/frame average
> running: "benchmark/creation/delegates_text_styled.qml"
>      125 ops/frame
>      125 ops/frame
>      126 ops/frame
>      126 ops/frame
>      125 ops/frame
>      125.4 ops/frame average
> running: "benchmark/creation/delegates_tworects.qml"
>      314 ops/frame
>      312 ops/frame
>      313 ops/frame
>      314 ops/frame
>      315 ops/frame
>      313.6 ops/frame average
> All done...
> 
> —
> 
> Being able to do 500+items rectangles in one frame is decent, but not awesome. Being able todo 130 text items in one frame, is less than ideal, given that we often use several text items per cell in a list or table. Text is probably the most important UI element we have. Being able to do 10 buttons is, well, unfortunate :) If we look at Button, we see that it is a fairly complex QML beast. Hierarchy is 
> 
> Button -> BasicButton -> Control -> FocusScope
> 
> and there are quite a bit of stuff on every level, including the dynamic style handling which will in turn create a StyleItem. 
> 
> And keep in mind that even though this isn’t the most high-end mac, it is sitll a pretty decent computer, Qt is supposed to run on much worse hardware than this.
> 
> —
> 
> There have been a few changes going into 5.5 which make these numbers better than 5.4, but I still think we got quite a ways to go. 

That’s very interesting.

Do you think it was ever better in past versions?

What do you think we should do about it?  Mainly focus on trying to create fewer objects, or is there still a lot of headroom for making the creation more efficient?  Is creation expensive because of constructor code, making too many signal/slot connections, or something else?