Amit Banerjee blogged a very usefull article about how to analyze the performance and usage of your Reporting Server (SSRS) with Power Pivot and Power View:
I recently needed to query report execution statistics for a SQL Server Reporting Services instance where the number of rows were quite large. So I decided to use Excel 2013 and PowerPivot to analyze the data. This would allow me to directly pull all of the data into an Excel sheet and then perform analysis on the extracted data without having to query the Report Server database repeatedly.
Leverage PowerView’s interactive capabilities to view the Report execution statistics, the report processed status (failure or success) and the processing, rendering and data retrieval times for each report.