use_cuda: True, has_backward: True method0: 0.0344547653198242, batch_size: 1, size: 50, num_rois: 300 method1: 0.1322056961059570, batch_size: 1, size: 50, num_rois: 300 method2: 0.1307379817962646, batch_size: 1, size: 50, num_rois: 300 method3: 0.2016681671142578, batch_size: 1, size: 50, num_rois: 300

Referenc: https://github.com/blackyang/compare_roi_pooling_speed

see also: http://www.cnblogs.com/king-lps/p/9026798.html