trickle is a portable lightweight userspace bandwidth shaper, that either runs in collaborative mode (together with trickled) or in stand alone mode.
It works by preloading its own socket library wrappers, that limit traffic by delaying data.
Trickle runs entirely in userspace. 
Install the package.
If you are running the daemon (see below), just start any program with "trickle" in front of it:
# trickle pacman -Syu
Otherwise also specify upload and download limit as well as other configuration options (see trickle(1) for more information):
# trickle -d200 -u50 pacman -Syu
Modifying other systemd services
ExecStart for a desired systemd service, appending
/usr/bin/trickle. For example:
Use with rsync
Instead of putting trickle in front of the rsync command (which won't work, since rsync presumably forks the ssh process), you call rsync like this:
rsync --rsh="trickle -d 10 -u 10 ssh" SRC DEST
If you want to have application specific settings with trickled, create the optional
/etc/trickled.conf file as described in the trickled.conf(5) man page. For example:
[ssh] Priority = 1 Time-Smoothing = 0.1 Length-Smoothing = 2 [ftp] Priority = 8 Time-Smoothing = 5 Length-Smoothing = 20