Slowness in report server

Hi,

We are facing some slowness in report server.Our reports are deployed in Windiws 2008 R2 Service Pack 1.When accessing the reports it is very slow.But after restarting the reporting services it is very fast and able to get the data with in 2-3 seconds.

Please let me know why it is retrieving the data very quickly after restarting the services.Do i need to change any setting in report config file or issue due to any memory.

Thanks,

Vijay