Devstack uses journald for logging, and the timestamp is actually generated by journald, not the OpenStack services. The journalctl command has options for displaying microseconds.

When journald is not used, the log format is set by logging_context_format_string andlogging_default_format_string. You can also try log_date_format. These config variables are used by all services, not only Nova, and print milliseconds by default. See https://docs.openstack.org/nova/lates... and https://docs.openstack.org/oslo.log/3....