failed generate trace file with mpirun

Hi, 

My application is a python program and mpi is called as mpi4py(built with intel mpi), and it needs to be killed during the runing(it needs a long time, we only profile a little). I use LD_PRELOAD=libVTfs.so mpirun -trace -n 2 python My application, it didn't generate stf as doc said. It only generate a file folder which contains stat-0.bin and stat-1.bin(filesize=0), any wrong with my configure? I already source mpivars.sh, itacvars. Thanks very much!