VNC faster than Spice for remote access to KVM guest?

hdave asked:

Having used RDP before, I’m not exactly thrilled with the performance I am seeing from VNC to my KVM virtual machines. The KVM host is Ubuntu 12.04 server x64. I’ve read that Spice is faster, and so after considerable bumbling around, I got it to work via both virt-manager (e.g. virt-viewer) and a standalone spice client.

I don’t have any hard and fast figures to quote here, but the VNC remoting seems 2x to 4x faster than spice! For example, in VNC I can easily watch a Flash video, but in Spice it is very choppy. In general Unity runs ok over VNC, but is laggy over Spice.

Is this possible? Is something misconfigured?

In both cases, I am connecting to the virtual host manager from a laptop (running Ubuntu 12.10) on the LAN to view an Ubuntu 12.04 Desktop guest VM on the host. The VNC configuration on the guest used the vga display type and the spice configuration used the qxl display type. I didn’t muck with the default amount of video RAM in either case.

My answer:

Ubuntu 12.04 is end of life, of course, but I do want to note that SPICE/QXL of that era was very early code, and on Ubuntu 12.04 in particular wasn’t well integrated yet. They were still finding and fixing SPICE/QXL bugs causing slowness well past 2013. These days I don’t think this question really applies anymore; SPICE is far faster than VNC for any version out in the last few years.

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