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Old 11-06-2018, 07:07 AM   #1
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Join Date: Nov 2018
Posts: 4
Exclamation Macbook Pro late 2016 and 4k monitor Dell P2415Q input lag only @ HiDPI scaling


I'm user of Apple MacBook Pro late 2016. Spec:
- Intel Core i5 2 GHz
- 16 GB
- Intel Iris Graphics 540 1536 MB
- Mojave 10.14.1 (18B75)

Today I bought external UHD 4K monitor Dell P2415Q (3840px x 2160px). I've connected it via Displayport. It works fine on its nominal resolution (@60Hz) (which is of course unusable, everything is too small), but it gets problematic when it comes to scaling.

First weird thing I noticed that I have both 1080p and 1920x1080 on the list which as I assume are both the same. Anyway:

- 1080p@60hz looks blurry and lowfi
- 1920x1080@60hz has gui/input lag which is most visible when moving mouse cursor (It jams every few seconds), but it lags overall (video, typing, gui animations, etc)

I've noticed that even if monitor is connected, when I move mouse to the builtin macbook's display, it starts to move fine and smooth. Even if there is video played on Dell's monitor. And even if I connect my old AOC Full HD external monitor.
With 2 displays connected mouse jamming and gui lag is visible only on Dell and only on that HiDPi scalling resolution. Everything on others screens works smooth and fine.

It didn't help when I plugged out AOC and went to closed clamshell mode. It's strange to me, because I've never experienced lag on my macbook pro and I've never had a problem with scaling on builtin display.

It occurs only on HiDPi resolutions. Funny thing is that it works fine on 2560x1440, but lagging on HiDPi 1280x770 which is actually the same resolution but with gui scalling.

My first idea was lack of graphic card power. But if so why everything works fine when all displays are connected. I can notice lag only on Dell. Moreover, I have Microsoft Windows 10 installed as a second system using Bootcamp and I'm not experienced lag on it.

I've DisplayLinkDriver 5.0 (42) installed. Dock station is i-tec USB 3.0/USB-C with DisplayLink DL6950 chipset.

Video of the problem (first I'm showing Dell and then Macbook's display):

Please help guys.

Last edited by piotrekfraacek; 11-06-2018 at 07:13 AM.
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