Report generation taking so much time

[tamuna]

Hello,

I'm Making  grouped report with crosstab according to the following layout:

 

ParentUnit

  SonUnit

ParentOption

  SonOption

SUM(data

ParentUnit2
  SonUnit
ParentOption
  SonOption
SUM(data)

 

The datasource i am using is flat ({parentunit, sonunit, parentoption, sonoption, sum(data)})

Report generation takes too much time 

can you give advice how report can be optimized.

thanks