I would like to note that each update action over a cell in RadGridView will perform refresh operation of the grid. The more updates you have, the more refresh operations will be performed. This is expected to affect the performance.
The appropriate solution that I can suggest is to wrap the foreach loop in a BeginUpdate/EndUpdate block. Thus, the refresh operation will be executed only once after calling EndUpdate.
foreach (GridViewRowInfo row in this.radGridView1.Rows)
row.Cells.Value = "update";
I hope this information helps. If you need any further assistance please don't hesitate to contact me.
Dess | Tech Support Engineer, Sr.