there seems to be some overhead between SQL Server 2005 and a CLR function
written in C#. Why is this?

I have a simple wraper around System.Diagnostics.Stopwatch.GetTimestamp() :

public partial class UserDefinedFunctions
{
   [Microsoft.SqlServer.Server.SqlFunction]
   public static long GetTimestampF()
   {
       return System.Diagnostics.Stopwatch.GetTimestamp();
   }
};

but if i run this it is hardly accurate. the time of getting from sql server
to a CLR function seems to be relatively slow for nanosecond calculations:

DECLARE @before bigint
DECLARE @after bigint
SET @before = dbo.GetTimestampF()
-- do something
SET @after = dbo.GetTimestampF()
SELECT @after - @before as nanoseconds

is there nyway to elimitate this overhead so that dbo.GetTimestampF()
executes as fast for TSQL as it is to call GetTimestampF() in C#?

If i call my GetTimestampF() on c# it executes fast enough for the
nanosecond results to be accurate