TigerVNC viewer is very slow when stretched over two 32" 4K Monitors

[soorajsram]

Describe the bug
I've a Mac M1 Max 32GB Memory, running on Sonoma 14.4.1 and hooked up to two Dell 32" 4K monitors through an OWC Thunderbolt4 dock (DP->Thunderbolt4 cable). I've no issues running applications other than tigerVNC. Issues are when the tigerVNC window is stretched over one of the monitors with 4k resolution (3839x2132). Anything in the VNC session becomes really slow. I mainly use this for hardware design and my tool runs really slow in it; i could really see the pointer in the VNC lagging behind the native curser in the Mac. Also navigating in the VNC session becomes really difficult as everything gets really slow. Issues get even worse when the window is stretched over 2 monitors in 4K resolution (7680x2132). If i stretch the VNC window to occupy only the quarter area of a single 4K monitor, i see a considerable performance change (gets better); at this kind of a reduced window size, the VNC resolution is automatically adjusted to 1920x1080. Also, i tried changing the 4K monitors resolution to 1080p; even that gets a better performance. But the issue is everything in the VNC gets too large and its not a friendly working setup.

To Reproduce
Steps to reproduce the behavior:

1. Connect two 32" 4K monitors to a Mac M1 Max (didn't get an opportunity to try it with a machine higher than M1) using thunderbolt4 cables in extended mode
2. Set the resolution of the monitors to 4K
3. Open tigerVNC with auto resolution scale
4. Stretch the VNC window to cover entire two monitors in extended mode
5. Open anything in the vnc session and observe the mouse pointer trailing and overall slowness in the session

Expected behavior
Expecting nothing to get slower in the VNC session and expecting the mouse pointer in the VNC to closely follow the native curser when the mouse is moved around.

Screenshots
I can share a video of this issue if that help (later if really needed)

Client (please complete the following information):

• OS: MacOS Sonoma 14.4.1
• VNC client: TigerVNC
• VNC client version: v1.13.1
• Client downloaded from: github

Server (please complete the following information):

• OS: CentOS Linux 7
• VNC server: vncserver-1.0-1.el7.noarch

[CendioOssman]

Thank you for your bug report.

If even the cursor is slow, then it sounds like the base OS is overloaded somehow. Given that this is a dock, the outputs might be driven using a USB graphics card rather than a "normal" one. Those can unfortunately easily be overwhelmed.

Do you have the same issue if the monitor is hooked up directly to the computer?

[soorajsram]

I’ve tried this with a single monitor hooked up directly to the Mac using a DP-Thunderbolt4 cable and I feel the same slowness in the VNC. Thanks Sooraj

…

On Tue, 16 Apr 2024 at 12:30 AM, Pierre Ossman (ThinLinc team) < ***@***.***> wrote: Thank you for your bug report. If even the cursor is slow, then it sounds like the base OS is overloaded somehow. Given that this is a dock, the outputs might be driven using a USB graphics card rather than a "normal" one. Those can unfortunately easily be overwhelmed. Do you have the same issue if the monitor is hooked up directly to the computer? — Reply to this email directly, view it on GitHub <#1747 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BH3KPYTIEZ2EOAAPBLJT2MLY5THRVAVCNFSM6AAAAABGITW3LWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDANJYGQZDAOJWGQ> . You are receiving this because you authored the thread.Message ID: ***@***.***>

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[soorajsram]

Any update on this?

[soorajsram]

Is there a specific memory and # of cores that you recommend for the vncserver to support a tigerVnc window extended over two 32" 4K display resolution? Is there an optimum config for this and also something good to have?

[CendioOssman]

I just noticed that the server is extremely old. The issue might simply be that it fails to keep up. Can you try TigerVNC 1.13.1 instead?

TigerVNC doesn't require a lot of memory, and the server is single threaded. Running two 4K screens with a lot of updates is demanding, though, so you'll need a fast CPU for a good experience.

Which desktop environment are you using? If it's the default GNOME, then it will likely not perform smoothly in such a scenario as it is designed with GPU acceleration in minde.