Many thanks for this hint. I never heard about LLVMpipe before and looked up what it means. The article that I found about is here:
http://www.phoronix.com/scan.php?page=news_item&px=MTAxM...
What I find interesting in this article is the following:
"[...] For those not familiar with the open-source LLVMpipe driver to begin with, read my original article on LLVMpipe from last year. Its performance has improved in the two or so years I have been closely monitoring this unique driver and fairs better with newer CPUs. [...]"
"[...] This testing was being done with the un-accelerated Cirrus X.Org driver (xf86-video-cirrus) in the KVM/QEMU guest from an Ubuntu 11.10 host. When allowing the Fedora Rawhide guest to only access one CPU core and 1GB of system memory, the performance of GNOME Shell over LLVMpipe was choppy and not as fluid as the GNOME3 panel fall-back or obviously when taking advantage of GPU hardware acceleration on bare metal. When allowing the virtual machine to take advantage of two CPU cores, the experience was much better, with still only 1GB of RAM. Red Hat has reported that using SPICE also improves the experience for GNOME Shell on this Gallium3D-based software driver. [...]"
