creating a pie chart takes too long

I have this same question in the "SQL Server Data Tools" forum also, but thought I should move it to the SSRS forum.

Why does creating a pie chart take so long?

I have a stored procedure that returns one row of data with several columns to SSRS to produce a pie chart.

The parameters for the stored procedure are a begin date and end date.

When I specify a date range of 1 day the stored procedure in SSMS takes 0 seconds, and SSRS takes about 3 seconds to display the pie chart when providing the same date parameters.

When I specify a date range of 31 days the stored procedure in SSMS takes 7 seconds, but SSRS takes so long to display the pie chart that I cancel the process.

Some of the numbers returned by the sproc are rather large when 31 days are sprecified, hence SSRS may be choking when trying to produce some percentages ... for example