How to fix “repaints on scroll” performance issue?

In my app I have a grid which is populated with at least 30 rows. When running sencha app inspector in chrome it tells me that this grid "repaints on scroll" and, indeed, it lags a little on chrome, while in ie my app almost freezes.

How to fix this?

edit: This is my gridpanel

Code:

Ext.define('tabInfo',{
           extend:'Ext.grid.Panel',constructor:function(config){
            //performing some initialization, like defining columns, store,etc.
this.superclass.constructor.call(this,{        id:'gridInfo',        store: store,           selModel: checkboxModel,         columns: columnsArray,        columnLines:true,        frame:true,        bbar:Ext.create('Ext.PagingToolbar',{            store: store,            displayInfo:true,            displayMsg:'Displaying topics {0} - {1} of {2}',            emptyMsg:"No topics to display"}),        tbar : topBar    });    store.load({params:{            start:0,            limit: itemsPerPage        }});

How to fix “repaints on scroll” performance issue?