Below is my code multi threading where large amount data increased in datagridview performance issue execution time decreased

try
            {
                Stopwatch stpcycle = new Stopwatch();
                stpcycle.Start();
                Trace.TraceInformation("SSCCAdded on grid  {0},{1},{2}", DateTime.Now.ToString(), SSCCCode, deck.ToString());
                DataGridView DGSSCC  = RetDG(deck);
                
                if (DGSSCC == null) return;
               
                //if (DGSSCC.InvokeRequired == true)
                //{
                //    InvokeUIHandlerG d = new InvokeUIHandlerG(SSCCAdded);
                //    this.Invoke(d, new object[] { SSCCCode, deck });

                //}
                if (DGSSCC.InvokeRequired)
                {
                    InvokeUIHandlerG d = new InvokeUIHandlerG(SSCCAdded);
                    DGSSCC.BeginInvoke(d, SSCCCode, deck);
                }

                else

                {

                    string SSCC = Convert.ToString(SSCCCode);
                    string printedSSCC = string.Empty;
                    for (int i = 0; i <= DGSSCC.RowCount - 1; i++)
                    {
                        printedSSCC = (string)DGSSCC[(int)DGSSCC_Col.TertiaryUID, DGSSCC.Rows[i].Index].Value;                       
                        if (printedSSCC == SSCC || string.IsNullOrEmpty(SSCC))
                        {
                            return;
                        }
                    }

                    object[] param = new object[3];
                    Trace.TraceInformation("SSCC ADDED INdex " + (CaseStartVal + DGSSCC.Rows.Count));
                    param[(int)DGSSCC_Col.CaseNum] = (CaseStartVal + DGSSCC.Rows.Count);
                    if (Globals.JobType == PTPL.JOB.Cust_GTIN_JbTypes.CIP.ToString() && deck.IsTertiaryDeck() == false)
                        param[(int)DGSSCC_Col.TertiaryUID] = string.Empty;
                    else
                        param[(int)DGSSCC_Col.TertiaryUID] = SSCCCode;
                    param[(int)DGSSCC_Col.UIDVerified] = false;

                    DGSSCC.Rows.Add(param);

                    int Index = DGSSCC.RowCount - 1;
                    if (Globals.App_Setting.Instance.uSER_SETTINGS.IsSortVerifySSCCTabDescending)
                    {
                        Index = 0;
                        DGSSCC.Sort(DGSSCC.Columns[(int)DGSSCC_Col.CaseNum], ListSortDirection.Descending);
                    }
                    else
                    {
                        DGSSCC.Sort(DGSSCC.Columns[(int)DGSSCC_Col.CaseNum], ListSortDirection.Ascending);
                    }
                    DGSSCC.Rows[Index].Cells[(int)DGSSCC_Col.TertiaryUID].Style.Font = new Font(DGSSCC.Font, FontStyle.Regular);
                    DGSSCC.Columns[(int)DGSSCC_Col.UIDVerified].Visible = true;
                    if (deck.IsTertiaryDeck())
                        DGSSCC.Columns[(int)DGSSCC_Col.UIDVerified].ReadOnly = true;

                    if (DGSSCC.RowCount == 1)
                    {
                        DGSSCC.Rows[Index].Selected = true;
                        scrollGrid(DGSSCC);
                        DGSSCC[(int)DGSSCC_Col.UIDVerified, Index].Value = true; //for visibility issue
                        DGSSCC[(int)DGSSCC_Col.UIDVerified, Index].Value = false;
                        //UpdateParentVerification(DGSSCC[(int)DGSSCC_Col.SSCC, Index].Value.ToString(),false);
                    }
                    else
                    {
                        DGSSCC[(int)DGSSCC_Col.UIDVerified, Index].Value = false;
                    }
                    DGSSCC.Refresh();

                    Jobdeck JD = Jobdeck.RetJobDeck(deck);

                    if (JD.printer != null && JD.printer.IsLinePrinter)
                    {
                        BTN_REPRINTLast.Enabled = false;
                    }
                    else
                    {
                        if (DGSSCC.Rows.Count == 0)
                            BTN_REPRINTLast.Enabled = false;
                        else
                            BTN_REPRINTLast.Enabled = true;
                    }

                    if (DGSSCC.Rows.Count == 1)
                    {
                        dg_ColumnHeaderMouseDoubleClick(DGSSCC, null);// added for proper allignment of datagrid
                    }
                    if (Globals.App_Setting.Instance.uSER_SETTINGS.IsSortVerifySSCCTabDescending)
                    {
                        DGSSCC.Sort(DGSSCC.Columns[(int)DGSSCC_Col.CaseNum], ListSortDirection.Descending);
                    }
                }
                stpcycle.Stop();