asp.net fileupload服务器控制性能

I have a fairly simple aspx page (using a MasterPage) with various buttons and server-side event handlers. When I click the buttons the event handler is hit almost immediately. However, as soon as I add the following to my page: asp:FileUpload runat="server" ID="fileUpload"" there is a huge increase in the delay between a button click and it's event handler, the fileUpload control is not used at this point. page (using a Maste