OpenLayers measure map rendering time

I am using OpenLayers version 3 (answers with ver 2 are also OK) and want to measure how long it takes to render the vector layer. So, I have a vector layer with features:

var vectorLayer = new ol.layer.Vector({
    source: vectorSource
});

And my map object:

var map = new ol.Map({
        renderer: 'canvas',
        target: document.getElementById('map'),
        view: new ol.View({
            center: [550000, 6520000],
            resolution: 500,
            minZoom: 1,
            maxZoom: 10,
            zoom: 1,
            resolutions: [500.0, 250.0, 125.0, 62.5, 31.25, 15.625, 7.8125, 3.90625, 1.953125, 0.9765625, 0.48828125],
            projection: projection
        })
    });

I want to measure how long it takes to render all features from the layer. If I do like this

 var start=performance.now();
 map.addLayer(vectorLayer);
 var time=performance.now()-start;
 console.log(time)

then I see time in console much much earlier than points on map. I want to see the time right after all points are rendered. How can I do that?