C# StreamWriter log batch message sync and async

using System;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Threading.Tasks;

static StreamWriter Syncsw = new StreamWriter("SyncSW.txt", true, Encoding.UTF8);
        static StreamWriter Asyncsw = new StreamWriter("AsyncSW.txt", true, Encoding.UTF8);
        static int maxTimes = 10000000; 
        static void Main(string[] args)
        {
            TestSync();
            TestAsync();
        }

        static void TestAsync()
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            Task t = Task.Run(() =>
            {
                for (int i = 0; i < maxTimes; i++)
                {
                    string msg = $"{i}i,Guid:{Guid.NewGuid().ToString()}";
                    LogMsgASync(msg);
                }
            });
            t.Wait();
            sw.Stop();
            string cost = $"Async cost {sw.ElapsedMilliseconds} milliseconds";
            LogCost(cost);
        }

        static void TestSync()
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            DoWork();
            sw.Stop();
            string cost = $"Sync cost {sw.ElapsedMilliseconds} milliseconds";
            LogCost(cost);
        }

        static void DoWork()
        {
            for(int i=0;i<maxTimes;i++)
            {
                string msg = $"{i}i,Guid:{Guid.NewGuid().ToString()}";
                LogMsgSync(msg);
            }
        }

        static void LogMsgSync(string msg)
        {
            Syncsw.WriteLine(msg);
        }

        static void LogMsgASync(string msg)
        {
            Asyncsw.WriteLine(msg);
        }

        static void LogCost(string cost)
        {
            File.AppendAllText("time.txt", $"Time:{DateTime.Now.ToString("yyyyMMddHHmmssffff")} {cost}{Environment.NewLine}");
        }