GNOME shell 3.12 and 3.13 are slow

[藍挺瑋 <lantw44 gmail com>]

GNOME shell became very slow after I upgraded it to 3.12 using this
Copr​http://copr.fedoraproject.org/coprs/rhughes/f20-gnome-3-12/ . I
also tried to build GNOME 3.13 using JHBuild, and it is also very slow.
Here is my screencasts recorded using Ctrl-Alt-Shift-R:

http://www.tfcis.org/~lantw44/videos/gnome-shell-slow-20140627-1609.webm
http://www.tfcis.org/~lantw44/videos/gnome-shell-slow-20140627-1618.webm


I am using Fedora 20 x86_64 with Linux 3.14.8 and Mesa 10.1.5.