[Interest] Optimizing performance with hundreds of widgets

[Elvis Stansvik]

2017-02-21 13:27 GMT+01:00 Elvis Stansvik <elvstone at gmail.com>:
> 2017-02-15 18:28 GMT+01:00 Gibbs, Matt <mgibbs at slac.stanford.edu>:
>> Hi All,
>>
>> I’m working on a Qt-based project to display rapidly updating information from a control system.  I want to display hundreds of signals, each updating at about 10 Hz.  As a performance test, I’ve thrown 500 Labels in a grid layout, and fire a timer every 100 ms which calls setText on each label.  This ends up being surprisingly CPU-intensive: on reasonably modern hardware (2012 MacBook Pro), I use 70% of one CPU.  This doesn’t leave me much overhead to do anything else.
>>
>> Are there any best practices to reduce CPU usage in this case?
>
> Hm, I don't really have a good answer when it comes to optimizing it
> the way you've stated it, but lets get a little philosophical instead:
> What human operator of your GUI is going to be able to process all
> this visual information? I would have a hard time monitoring even 5
> labels of text updating at that rate.
>
> My recommendation would be:
>
> 1. Consider if your really have to show all these sensors, or if the
> information they're conveying can be aggregated in some way.
> 2. If you really need to visualize them all at once, consider a
> simpler presentation than the numerical, such as a bar (should be
> cheaper to redraw than a changing text).
>
> Regarding 1, if the sensors can be grouped in some logical way, you
> can present a collection of sensor groups instead. Regarding 2, if the
> user wants to look closer at a single sensor, or maybe a (reasonably
> sized) group of sensors, you could build some UI for that.
>
> It would help to know a little more about the user story, is this for
> monitoring a system for failures? If so, I think the rule of thumb is
> that if nothing is out of the ordinary, the system should not look
> visually "busy" (no big movements or bright colors, just subtle
> gray/static text). That allows you to use visual movement and bright
> colors for error conditions / anomalies. But yea, it would help to
> know more about what the GUI is for :)

Another powerful UI design principle is (as I hinted at) "drill down"
UIs -- find some way of aggregating the information, and let the user
drill down deeper if he/she wants to know/see more.

The fidelity you're aiming for (500 numbers, presented numerically @
10 Hz) is too much bandwidth, not only for your MacBook, for also for
any human.

Elvis

>
> Hope that helps a little, even if it wasn't what you asked for.
>
> Elvis
>
>>
>> Cheers,
>> —Matt
>>
>> Matt Gibbs
>> SLAC Accelerator Operations Group
>> mgibbs at slac.stanford.edu
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