Using grafana to display info from the MYSQL master

Hello all, I feel this is really obvious task but I just cant sort it out.We have many Percona master/slave pairs which are monitored using prometheus-mysqld-exporter. I need to display the cpu load factor and other items for the master server within grafana. Has anybody got a grafana expression to isolate the master_hosts. It is  easy to get any stat for the slave. But how do I get info for the master?

IMHO it’s possible to fetch all slave services in a variable and then ignore such services in formulas.