- Windows 10 x64
- 2x NVIDIA GeForce 1080 Ti with SLI bridge connected, but SLI disabled.
- GPU 1: HP Z27q 5K, using 2x DisplayPort connectors in MST mode.
- GPU 1: Philips BDM4065 (4K display using single DisplayPort 1.2 connector) - this is my primary monitor that sits in-between the two 5K displays.
- GPU 2: HP Z27q 5K, using 2x DisplayPort connectors in MST mode.
This arrangement was working perfectly fine with no perceivable lag until around October of 2019 when my Philips BDM4065 4K display started to feel laggy. Initially I thought it was my computer mouse playing-up but I quickly determined that my Philips BDM4065 display was lagging exactly 1 frame behind the other two displays (I run at 60Hz, so that's 16.6ms lag). It came as a surprise because I had made no OS updates, my NVIDIA drivers were unchanged since April 2019, no hardware changes, etc.
But the really weird thing is that sometimes the lag will go-away and all 3 monitors will feel buttery-smooth. I noticed that some times the computer will be lag-free when I turn it on in the morning and then it will start to lag around 5-6pm or sometimes around 8pm. I can't find any obvious causes for this (I have Windows Night-Light turned off, and FWIW, I noticed that Night-Light actually introduced a bit of lag by itself). I also noticed that on days when the monitor is lag-free and I then lock my computer and Windows puts the monitors into sleep mode - when it wakes from sleep the monitor will have lag. I can reproduce this consistently (provided I can make it boot-up without lag in the first place).
Crucially, if I plug my Philips BDM4065 monitor into another computer (e.g. my laptop's docking station) then the lag disappears and it's buttery-smooth again.
Initially my Philips BDM4065 was plugged into the remaining DisplayPort in the second GeForce GPU, but after I plugged it into the remaining DisplayPort in the first GeForce GPU the problem seemed to be slightly improved (as though it was lagging by a half-frame) and then the next day there was no lag... until a few days later when the lag came back (initially after the computer had been on for a few hours). Right now, as I write this, it's been lagging all-day and it's driving me crazy (as the Philips BDM4065 already has barely-acceptable input lag of around ~25ms, so adding an extra 17ms pushes it into unacceptable 40ms+ lag).
I can verify that the Philips BDM4065 is lagging when compared to my other monitors by running this web-page I created in a browser that straddles two monitors (left side on one, right side on the other) and recording the screen with my iPhone's slo-mo (240fps) camera mode - here's an example showing the lag (the HP Z27q 5K is on the left, and the Philips 4K is on the right):
- IMG_4174.jpg (100.33 KiB) Viewed 2466 times
- IMG_4175.jpg (78.59 KiB) Viewed 2466 times
- IMG_4176.jpg (62.09 KiB) Viewed 2466 times
- Using a different DisplayPort cable (no change observed, both cables are DisplayPort 1.4 self-certified)
- Plugging the monitor into a different computer (the other computers don't have the lag)
- Plugging the monitor into a different port or GPU in the same computer (this resolved the problem, but then it came back again!)
- Updating NVIDIA drivers (this gave me a slight improvement, but full-frame lag still happens)
- Fiddling with NVIDIA's scaling settings (no difference observed at all, whether using GPU or Display-based scaling - but I'm running at native resolutions anyway)