Update only Changed Values from GridView

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C#3.0

C#

Hello Everybody,

While loading the form i am retrieving values from database and showing in datagridview . when i click save,all the values are being updated .It is working fine.But i have many rows so performance is slow.
This is code i am using and it is working fine.

foreach (DataGridViewRow examinationlistrow in dgvExamination.Rows)
            {
                string _examinid = examinationlistrow.Cells[0].Value.ToString();
                string _examinvalue = examinationlistrow.Cells[3].Value.ToString();
                UpdateListItem(mrid, ic, _examinid, _examinvalue);
            }

But i want to update only changed values of the datagridview.