问WhenAll是否增加了不必要的延迟？此外，是什么导致了执行时的离散尖峰(C#/.NET)

EN

using System.Diagnostics;
namespace ConsoleApp1
{
    internal class Program
    {
        static async Task Main()
        {
            for (int i = 1; i <= 100; i+=1) 
            {
                await RunTest(i);
            }
        }

        public static async Task RunTest(int count) 
        {
            var sw = Stopwatch.StartNew();
            var tasks = new List<Task>();

            // Construct started tasks
            for (int i = 0; i < count; i++)
            {
                tasks.Add(Task.Run(() => Thread.Sleep(250)));
            }

            // Test 1, WhenAll
            //await Task.WhenAll(tasks);

            // Test 2, 10ms loop
            bool completed = false;
            while (!completed)
            {
                await Task.Delay(10);
                completed = tasks.All(t => t.IsCompleted);
            }

            Console.WriteLine($"{count},{sw.Elapsed.TotalSeconds}");
        }
    }
}