Understanding of CPU buffer line

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Threading;

namespace Buff
{
    // [StructLayout(LayoutKind.Explicit, Size = 120)]
    // class Tclass
    // {
    //     [FieldOffset(56)]
    //     public long x = 0l;
    // }

    class Tclass
    {
       
        public long x = 0l;
    }

    internal class T01_CacheLinePadding
    {
        
        public static Tclass[] arr = new Tclass[2];

        public static long COUNT = 10_0000_0000l;
        public static System.DateTime startTime;
        public static void Main(string[] args)
        {
            arr[0] = new Tclass();
            arr[1] = new Tclass();
            startTime = System.DateTime.Now;
            //Run();
            RunOne();
        }

        public static void RunOne()
        {
            for (int j = 0; j < COUNT; j++)
            {
                arr[0].x = j;
                arr[1].x = j;
            }
            DateTime dt2 = System.DateTime.Now;
            TimeSpan ts = dt2.Subtract(startTime);
            Console.WriteLine(string.Format(" At present t1 Time for :{0}",ts.TotalMilliseconds));
        }
        public static void Run()
        {
            List<ManualResetEvent> list = new List<ManualResetEvent>();
            
            ManualResetEvent mre = new ManualResetEvent(false);
            System.Threading.Thread thread = new Thread((o) =>
            {
                for (int j = 0; j < COUNT; j++)
                {
                    arr[0].x = j;
                }
                ((ManualResetEvent)o).Set();
            });
            
            System.Threading.Thread thread1 = new Thread((o) =>
            {
             
                for (int j = 0; j < COUNT; j++)
                {
                    arr[1].x = j;
                }
                ((ManualResetEvent)o).Set();
            });
            
            list.Add(mre);
            thread.Start(mre);
            thread1.Start(mre);

            WaitHandle.WaitAll(list.ToArray());
            DateTime dt2 = System.DateTime.Now;
            TimeSpan ts = dt2.Subtract(startTime);
            Console.WriteLine(string.Format(" At present t1 Time for :{0}",ts.TotalMilliseconds));
        }
    }
}