Yeah I was aware of that but after seeing the video below it now appears that there’s a performance hit when using resolutions that aren’t 110 or 220ppi. I won’t be doing anything that taxes the GPU so it should be okay.
He mistakenly said there's a scale up and scale down process contributing to the performance loss. There's no scale up. The GPU does one transformation - from 5K down to 4K. Everything else is up to the application.
That video would be better if it gave same numbers. Some benchmarks with the following variables would be interesting:
Using displays (smaller displays have fewer pixels for the GPU to output but that doesn't really matter because a good scaler has to look at all the source pixels of the framebuffer defined by the display modes)
- 1080p, 1440p, 3K, 4K, 5K, 6K (some displays can accept custom timings that make them behave like a display of a different size see you don't need one of each display for a test)
Using non-retina modes (usually a user would use a display mode that is not larger than the display resolution - 1440p on 1440p display but not 4K on 1440p display)
- 1080p, 1440p, 3K, 4K, 5K, 6K
Using retina modes (retina modes makes objects 4 times larger, but once an object is drawn, it usually doesn't have to be drawn again unless it is moving)
- 1080p, 1440p, 3K, 4K, 5K, 6K (a 6K retina mode is actually 12K pixels wide - usually a user would use a retina mode that is smaller than the display resolution - 3K HiDPI on 4K display but not 4K HiDPI on 4K display)
Using different refresh rates (a lower refresh rate could have more performance since the GPU would be scaling fewer pixels per second)
24Hz, 30Hz, 48Hz, 60Hz
There's probably no such thing as a 3K display but you can just create a custom 3K timing 3008x1692. Scaling that is done by the display instead of the GPU will not have an effect on performance.
In the video, the user went to a 1440p display because a 4K display had low performance doing 1440p HiDPI. If you had a 4K display that can accept a 5K timing, then it could perform better at 1440p HiDPI since the GPU wouldn't need to do the scaling? My Acer XV273K 4K display can do 5K60 but only up to 8bpc. Do these 4K Dell displays (or any 4K display) support 5K input using DSC? Maybe it's not the scaling that causes the problem - maybe it's the quadruple number of pixels. The suggested benchmarks would determine that.
There's no way to do custom timings on M1 Macs so there's no way to get a 4K display to accept a 5K timing on M1 Macs unless you can spoof the EDID but I don't know of an inexpensive device that can do that for DisplayPort connection.
