Performance issues when running site in visual studio vs profiling

Question

This is a very strange issue that I am experiencing, and almost goes against anything logical that I can think of. I am currently profiling a website which we are building, which sometimes takes 5 seconds for a page to load. This happens both on IIS, and Visual Studio Development Server. However, when I profile it using ANTS Performance Profiler, it performs up to 5x faster, and loads in less than a second.

I am quite baffled as to why this can happen, because as far as I know, profiling should increase the time, not decrease it. Anyone could maybe shed some light on this?

Site is developed in Visual Studio 2010, ASP.Net v4.0, C#.

Answer 1

Performance testing needs to be done in carefully controlled setting. Things like system file cache, network, machine load, NGEN status, virus scanner could affect perf result.

Use Perfview to understand how 5s is spent (could be waiting for disk IO):

http://www.microsoft.com/en-us/download/details.aspx?id=28567

Answer 2

This is interesting as its very rare (I work on ANTS support). The main difference ANTS imparts on a process is permissions (since (usually) the process is fully initiated by ANTS and inherits the permissions). We have some routines that optimise the start-up procedure but I've never heard of a speed-up like this. Using Taskmanager, take a look at the login account that the process runs under ANTS and normally- then try to run your process under the account that ANTS uses. You may find this helps to explain the speed-up.