Best place to filter out on field

Hi, I have the following query to report on license utilization, and now want to filter out on specific slave indexers: index=_internal source=*license_usage.log type="Usage" | join type=left i [rest count=0 /services/licenser/slaves | rename label as slave | rename title as i | table i slave] | eval indexname = if(len(idx)=0 OR isnull(idx),"(UNKNOWN)",idx) | eval sourcetypename = st | bin _time span=1d | stats sum(b) as b by _time, slave, st | eval GB=round(b/1024/1024/1024, 3) | fields _time, slave, st, GB How would I do that, and where's the best place to put the filter in this query from a performance perspective? For example, I want a set of slaves, not all - slave=myservera OR slave=myserverb.