StopWatch

Stopwatch watch = Stopwatch.StartNew();

        using (RetailEntities context = new RetailEntities())
        {
          foreach (var entity in customers)
          {
            context.Customers.Add(entity);
          }
          context.SaveChanges();
        }

        watch.Stop();
        Console.WriteLine(string.Format(
          "{0} customers are created, cost {1} milliseconds.", 
          customerCount, watch.ElapsedMilliseconds));