<system.diagnostics>
  <trace autoflush="false" indentsize="4"></trace> // what's this for?
  <sources>
    <source name ="WebAppLog">
      <listeners>
        <add name="FileLog" type="System.Diagnostics.TextWriterTraceListener" initializeData="PartialView_WebApp.log" traceOutputOptions="DateTime,ThreadId,ProcessId,Timestamp,LogicalOperationStack,Callstack">
          <filter initializeData="All" type="System.Diagnostics.EventTypeFilter"/>
        </add>
        <remove name="Default"/>
      </listeners>
    </source>
  </sources>
</system.diagnostics>

public class Log
{
    static TraceSource source = new TraceSource("WebAppLog");
    public static void Message(TraceEventType traceEventType, string message)
    {
        short id;
        switch (traceEventType)
        {
            case TraceEventType.Information:
                id = 3;
                break;
            case TraceEventType.Verbose:
                id = 4;
                break;
            default:
                id = -1;
                break;
        }
        source.TraceEvent(traceEventType, id, message);
        source.Flush();
    }
}

public ActionResult Index()
{
    try
    {
        Log.Message(System.Diagnostics.TraceEventType.Information, "Index Action Start");
        // Do work
        Log.Message(System.Diagnostics.TraceEventType.Information, "Index Action End");
        return View();
    }
    catch (Exception ex)
    {
        throw;
    }
}

static TraceSource source = new TraceSource("WebAppLog");
source.Switch.Level = SourceLevels.Verbose;

<system.diagnostics>
     <trace autoflush="false" indentsize="4"></trace>
     <sources>
         <source name ="WebAppLog" switchName="mySwitch">
             <listeners>
                 <add name="FileLog" type="System.Diagnostics.TextWriterTraceListener" initializeData="c:tmptrace.log" traceOutputOptions="DateTime,ThreadId,ProcessId,Timestamp,LogicalOperationStack,Callstack">
                     <filter initializeData="All" type="System.Diagnostics.EventTypeFilter"/>
                 </add>
                 <remove name="Default"/>
             </listeners>
        </source>
    </sources>
    <switches>
        <add name="mySwitch" value="Verbose" />
    </switches>
</system.diagnostics>