Data Modelling(Star schema): Calculate Count of a Dimension based on another Dimension

Hi All,

I have performance issue while calculating the count of accountIds for a Partner Id, since we have a star schema and our fact table has millions of rows. The DAX measure uses crossfilter function which hampers the performance of the data model. In general in our organization we have lot of request on calculating dimension based on another dimension. With our current set up which is star schema it is hard to achieve these simple requests.

Here in the Picture below we have Accounts (Dimension) & Partners (Dimension) table which has relationship to RevenueDetails (Fact) table.
For example : Count of AccountId per Partner(One Partner can have multiple Accounts)

Could anyone suggest on how to tackle this problem?