I'm seeing horrible performance from the xfce window manager (xfwm4) on my main, everyday machine, but not on an older backup machine or on any of the linux virtual machines I run on virtualbox.
The symptoms: moving a window with the mouse is so slow as to be painful, and the CPU usage (on one of four CPUs) jumps to 100% almost immediately (xfwm4 is the culprit, see below). If I open an xterm and run (for example) "/usr/bin/marco --replace", this sluggish behavior returns to normal immediately. After wasting hours on google I finally noticed that I had compiled x11-wm/xfwm4 with the xcomposite useflag disabled, so I enabled it and re-emerged xfwm4. Now I can get decent performance from xfwm4, but only if first I turn on compositing by running xfwm4-tweaks-settings. (No, not by running the puny and feeble xfwm4-settings app: I need to invoke a "tweak" to make xfce4 an acceptable Desktop Environment on my main desktop machine. <official rant mode> I remember going through this same frustration with gnome3, which was (and is) unusable without installing the gnome-tweak-tool package and using it to customize settings that I still don't understand. (That's why I finally gave up on gnome3, and I may yet give up on xfce4 and go back to mate.) Note that I'm not turning off <official rant mode> yet, but I should mention that this machine is ~amd64 with ati-drivers-15.7 and vanilla kernel 3.14.51. (Same problem with gentoo-sources-3.18.19, BTW.)
