Devstack does not run services :)
Devstack runs as screens, if you want to restart any OpenStack service, get into screen using screen -r.
For example to restart nova network:
- Go to nova network screen which is screen 9, using the command CTRL+A followed by 9.
- Kill the nova network using CTRL+C
- Restart it using "up" arrow and enter.
**Remember you cannot reboot your machine running devstack. For further details see this article.