When using powerline in tmux with standard configuration but without having py37-psutil installed manually, the following warning is constantly displayed (and uptime is missing from the status bar):
WARNING:tmux:uptime:Unable to get uptime. You should install psutil module
I use the out of the box configuration, .tmux.conf only contains one line:
This warning goes away when manually installing py37-psutil.
I would therefore suggest to add py37-psutil as runtime port dependency.