Use Tablet For Pointer option causing CPU usage on Linux

cfnz

Member
Feb 12, 2019
7
2
8
53
Hi,

Just testing proxmox... I was getting around 5-6% CPU usage on two different linux boxes on two different test servers, but in the guest, cpu usage in top was not really showing anything.

I have done some searching and found a couple of several year old posts that talked about the Tablet for Pointer option and context switching... seemed to be more about windows guests.

Anyway, I turned it off and immediately (without rebooting the guest), the CPU usage dropped (see pic in attachment). The docs don't really talk about what this option is for, from what I can gather it is for gui mouse control in the guest.

Why would one turn this on (the posts talked about some drivers that could be used instead anyway).

Should it be on by default? And is there a way to turn this off by default? (Or is there another issue at play that should be fixed in my setup or elsewhere?)

upload_2019-5-8_12-41-55.png

Thanks for any help.
 

masgo

Member
Jun 24, 2019
45
3
13
72
I experienced the same. A question out of curiosity: what exactly does this option do?

Is there any Difference if its on or off if I only access the VM via SSH or RDP and never by using the proxmox VNC?
 

CRCinAU

Member
May 4, 2020
67
29
18
It emulates a USB tablet as a mouse - as that's more accurate for VNC tracking of the cursor.

As its a USB device, it gets polled at ~1000hz. That's the CPU usage you see.
 

masgo

Member
Jun 24, 2019
45
3
13
72
As its a USB device, it gets polled at ~1000hz. That's the CPU usage you see.

Makes sense to cause such a high CPU Load if its polled at that frequency. The question is: why on earth such a high polling rate? Even for gaming this is, most of the time, to much. Why not the very common 125 Hz?

Also, can the polling rate be changed? Using the mouse without "tablet mode" is quite cumbersome, but having a constant 12% CPU load (in my case) for only occasionally using the VNC connection is a bad trade-off.
 

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