Windows guest desktop refresh rate is assumed to be 60Hz

[Donuts]

Host: Lubuntu 16.04 x86-64, Nvidia binary driver Guest: Windows XP SP3

The host desktop vertical refresh rate is 50Hz.

The XP guest emulated vertical refresh rate is 60Hz. For example, Display Properties -> Advanced -> Monitor tab allows only one setting for Screen refresh rate: 60 Hertz.

Programs running in the guest which calibrate their timing to the Windows desktop refresh rate "see" a refresh rate of 60Hz, not the host's actual 50Hz rate.

To fix that, perhaps the guest graphics driver could have other selectable refresh rates?

[Mihai Hanor]

The guest screen is an emulated (virtual) screen, it has nothing to do with the host's screen and its refresh rate. The latter is a consequence of how real video hardware works. The guest runs with emulated hardware devices, including the guest screen and the guest video card. If I want/need to, I can force the guest to emulate a 200Hz refresh rate on its virtual screen, while the host runs with it's usual 60Hz screen refresh rate.

[Donuts]

Right, I understand that. What I'm asking is that there be some way to have the guest emulate a different refresh rate to the single hard-coded 60Hz one.

Since I use a 50Hz host refresh rate, I'd like to be able to tell the guest to use 50Hz (emulated) refresh rate. Then programs running in the guest which sync to (what they think is the) vertical blank would at least show smooth-ish graphics, instead of juddery with-dropped-frames graphics (where the guest program outputs 60 frames/sec but the host display can only show 50).

[Simon Coleman]

Only the hardware really interacts with the monitor refresh rate, its about how often the current contents of the video ram current frame is refreshed onto the monitor. Guest programs just write to video ram (in windows case via the O/S api in any case, even 'low level' graphics going via one of several rendering API).

So although your request is reasonable (offer a different video refresh rate) it is not responsible for the laggy graphics that you see - that's to do with the video card emulation provided by vbox & its ability to convert that into real video draw for the host [which then paints to monitor via video ram]

Somewhere there is an underperforming element in your host system (& it is dropping chunks of graphic rewrite to keep up with where the new content should "now" be) or could just be that the workload in the guest means it is dropping the content for the same reason.

I would check the workload on both machines (cpu/memory/disk io) & drivers (esp. guest additions for your current vbox version) & that similar content works natively on the host.

I suspect there will be a number possible issues & hope you have good fortune in identifying the cause.