SharePoint 2010 Troubleshooting: Server Reporting Services Report Times Out

What to do when an SSRS report times out? This sort of problem can be really hard to troubleshoot, but here's what you can try:

First of all, check how the SQL query performs. If it's running slow, than the problem is query related instead of SSRS report related and you'll need to work on that part.
Check if the amount of data rendered by the report is the problem. Do this by creating a new report that displays the results of your query in the simplest way possible. If it takes a long time to render, you're displaying to much data on a single report and you need to either change the amount of data shown in the report or look for another reporting technology and test if that's able to perform better (such as Silverlight Chart Controls).
Now add the report logic (if there is any) step by step, and see when it breaks.
As an alternative. It's possible that somehow the .rdl file got corrupted. Rebuild it step by step, including the same query and logic. There have been cases where that process solved the problem completely. This is another path you can follow.

To do

Add references about SSRS related log files and specific SSRS performance counters.