Question

We are debugging some performace problems and have notice some strange results from stopwatch.

1. We have a client that calls a web service
2. We log the time at the service layer og the web service with stop watch
3. We log the time at the lower layer with datetime.now.ticks

Layer 2 is just a pass through layer with 2 lines of logging.

The times recorded are:

1. 110 ms
2. 52125 ms
3. 125 ms

We had expected 2 to be less than 1, although no api is accurate to 1 ms.

We create a new stopwatch in each service call so this is not the time of an old stopwatch thar has been restarted.

Anyone know why we are getting these figures?

Edit

2 and 3 are on the same machine and the same app domain

The stopwatch code is:

            var sw = new Stopwatch();
            sw.Start();

            //code to call layer 3

            sw.Stop();
            orchestrationContext.LogOperationTime(functionName, sw.ElapsedMilliseconds);

logging of time in layer 3

    protected DateTime StartTime { get; set; }
    StartTime = DateTime.Now;

    // code 

    new TimeSpan(DateTime.Now.Ticks - StartTime.Ticks).Milliseconds

The logging of 1 is on a seperate machine, logging using Websphere.

Answer 1

Okay, your second code sample should be returning TimeSpan.TotalMilliseconds, using just Milliseconds you will get the sub second part.

Why aren’t you using a StopWatch in the layer 3 code, in the same style as your layer 2 code, it is more accurate?

Your question title is “Correctness of StopWatch” but it seems you are comparing bananas with peaches and apples. StopWatch will use a HighResolution timer if supported by your hardware or operating system otherwise it will fallback to a System.Timer which offers a granularity of around 15ms.

I can’t comment on how or whether to use WebSphere but it will not offer more accurate timing than StopWatch unless it uses an API to some other high accuracy time source.