Stored Procedure Performance when passing in mutli-values from a SSRS Report

try below

CREATE Procedure [reports].[report_Top20Values]
(
        @CalendarYearMonth INT,
        @AssetSubGroup VARCHAR(600)
)
AS 
BEGIN
;WITH CTE1 AS
(SELECT  distinct Val from dbo.fn_String_To_Table(@AssetSubGroup,',',1))
   select CalendarYearMonth,SomeValue
    from table1 g inner join CTE1 b on g.AssetSubGroupID = b.val
    where CalendarYearMonth = @CalendarYearMonth
END

Please give us the execution plan