When you run a report in the Microsoft SharePoint integrated mode in Microsoft SQL Server Reporting Services, the report may run noticeably slower than when you run the same report in native mode.
In SharePoint integrated mode, reports typically run slower than when the same reports run in native mode. One main cause of this latency can be attributed to SharePoint object model calls that are made. This issue is usually most noticeable where there are multiple Report Viewer Web Parts on a single page that is running small reports.
Other performance issues can usually be isolated to these two areas in SharePoint:
Reporting Services SharePoint plug-in. This plug-in makes many SOAP calls to the Reporting Services server.
SharePoint overhead performance, and this includes SharePoint object model calls. This overhead performance is primarily the cost of many of the SharePoint services and the SharePoint implementation of the SQL Server.
In SQL Server 2005 SP3, the number of SharePoint object model calls that SQL Server 2005 Reporting Services (SSRS) makes are optimized. This optimization reduces some latency when you compare report performance to native mode. Additional improvements were made in both SQL Server 2008 Reporting Services and SQL Server 2008 R2 Reporting Services as part of the maturation of the product and to improve the overall integration of these two products.
Please also see the following White Paper by the SQL CAT. This White Paper covers the overall performance aspects of Reporting Services in SharePoint mode versus native mode.
Reporting Services Performance in SharePoint Integrated Mode in SQL Server 2008 R2: