Functions to know it is begin and end of a .Net web request

Hi,

I am injecting my helper function calls to the web application requests to calculate the request time and to profile slow calls. Can i know what are the correct functions to choose for the beginning and end of each .Net Web application (in general to ASP.Net and MVC) ..? 

Is there any function that starts when the request starts and ends after completion of all the processes in that request?. So that i will inject only to that function for calculation time of request.

I am confused to select the functions to inject to calculate the time taken for the request and I will profile the function calls only in-between the begin and end functions of a request.

Thanks 

./Selva