Why the computational speed does not increase with the increase of GPUs?

From: sunyeping (sunyeping_at_aliyun.com)
Date: Wed Oct 21 2015 - 22:18:17 CDT

Dear all, I find increasing the number of GPU can not obviously increase the computational speed with NAMD. I've tested the computational speed of NAMD with two K80 GPUs and four K80 GPUs.  The simulation system are the same, which contains about 60 thousand atoms, and the NAMD version is NAMD_CVS-2015-10-21_Linux-x86_64-multicore-CUDA. With two K80 GPUs, the computaional speed was 0.0566 day/ns, which with four K80 GPUs, the speed was 0.0456 day/ns. So there was little improvement with doubling the number of divices. It seems that there are some defets in NAMD code. But how can improve this situation? Yeping Sun Institute of Microbiology, Chinese Academy of Sciences

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