Comment 4 for bug 21705

For fast-user switching, multiple X sessions are started on multiple virtual
terminals, but non-visible screensavers are still left running.

If one X login is being used (for example on vt7) and another is in the
background (eg. on vt9) then xscreensaver will continue to run unabated on the
background X server, in turn using up 50%-100% of the CPU.

xscreensaver can be put into 'suspend' mode and this should to done (perhaps
polling?) if the vt of the X session is not the currently visible vt.