Dear QE users, I am not a new user of quantum espresso. Previously I worked on a single machine of 4 core. I simply worked with mpi by 'mpirun -np 4', and the job was faster than a serial run. Now I have a 2 node cluster. Each node consists of 2 processors of 12 core each. Hence I made a hostfile(for a single node) by specifying "node1 slots=24". Now my command is "mpirun --hostfile my_hostfile -np 24 ph.x <input.in> output.out". This run takes 9hours and 39 minutes. But when I want to use both nodes by "node1 slots=24 node2 slots=24" & command "mpirun --hostfile my_hostfile -np 48 ph.x <input.in> output.out -ni 6 -nk 2", It is taking too much time to complete the job. Even it is now almost 26 hours over. 2nd q point calculation is going on.
NB: The job has only 4 q points. I have also seen this in pw.x run. In a single node, it is taking only 2mins. Command: mpirun --hostfile my_hostfile -np 24 pw.x <input.in> output.out. But in case of both nodes, it is taking almost half an hour. Command: mpirun --hostfile my_hostfile -np 48 pw.x <input.in> output.out Can anyone suggest me that why the jobs running on 2 nodes are slower than the jobs in single node? Thanks in advance. Regards Pratik Kumar Das *Pratik Kr. Das* Research Fellow High Pressure and Temperature Lab Faculty of Science Jadavpur University Kolkata 700032
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