‘cpu-sos’ is a buffer-local minor-mode designed to track the
visibility of buffers associated with sub-processes or EXWM managed
windows and send a SIGSTOP signal to those processes (and their
related ones) as soon as their buffers become buried, eventually
reverting this by sending a SIGCONT signal as soon as they become
visible again.  This has the effect of limiting CPU consumption of
processes managed by Emacs at the user’s discretion.  Useful for
programs whose background processing the user is not interested in.
For example, web-browsers running JavaScript aggressively on
background for no good reason.  Other legitimate use is to forcibly
disable background app notifications while one’s attention focus is
elsewhere.

CAVEATS: Notice that the concept of "visibility" used by this
package is defined by the semantics of the value ‘visible’ given to
the parameter ‘ALL-FRAMES’ of function ‘get-buffer-window’.  This
is necessary, but not sufficient for actual view of the buffer at
hand.  For instance, if a buffer is in a window of a frame that is
totally occluded by another it still is regarded as "visible",
although one can’t actually see it.  Aside from imprecise detection
of visual interaction, there is no attempt to detect sound
interaction.  Therefore, buffers running music players or recording
programs should not have this mode enabled.  The same is true if
one wants to have asynchronous processes delivering notifications
at arrival.  Keep also in mind that trying to yank selection from
stopped processes is problematic.