performance problem when using grid with checkbox

Hello, I am using the grid with checkbox. And I put a checkbox on the head to select all rows.
Usually it need 10s and 100% cpu to select all rows when the grid have 4000 rows which can not be accepted. And I have keep virtual mode on .

The code is as following. Is there any way to improve the performance?

obj.checkboxSellAll.onControlValueChanged = function(value){
       	 var obj=null;
           obj=  eval($("currentGridName").value);
         	  if(value){
                   var rows_array = new Array();
                   for(var i=0;i<obj.tabGrid.getRowCount();i++){
                    if (obj.tabGrid.getCellText(obj.idColIndex,i)!=''){
                      rows_array[i]=i;
                     } 
                   }
                   obj.tabGrid.setSelectedRows(rows_array);
                }else{
                  obj.tabGrid.setSelectedRows([]);
              }
         }

Help! Please.

Joseph,

maybe this can help -

http://www.activewidgets.com/javascript.forum.16116.9/select-all-rows-performance-problem.html

Thank Alex!