forward_timer.Start();
for (int i = 0; i < layers.size(); ++i) {
  timer.Start();
  layers[i]->Forward(bottom_vecs[i], top_vecs[i]);
  forward_time_per_layer[i] += timer.MicroSeconds();
}

caffe time -model examples/mnist/lenet_train_test.prototxt -weights examples/mnist/lenet_iter_10000.caffemodel -gpu 0 -iterations 10