Hello Jeff, Yes, I am using a switch and other machines are also connected with that switch. If I remove other machines and just use my two node with the switch, then will it improve the performance by 200 ~ 400 iterations? Meanwhile I will give a try with a single dedicated cable. Thank you. Best Regards, Abu Naser ________________________________ From: Jeff Hammond <[email protected]> Sent: Wednesday, June 20, 2018 12:52:06 PM To: MPICH Subject: Re: [mpich-discuss] osu_latency test: why 8KB takes less time than 4KB and 2KB takes less time than 1KB? Is the ethernet connection a single dedicated cable between the two machines or are you running through a switch that handles other traffic? My best guess is that this is noise and that you may be able to avoid it by running a very long time, e.g. 10000 iterations. Jeff On Wed, Jun 20, 2018 at 6:53 AM, Abu Naser <[email protected]<mailto:[email protected]>> wrote: Good day to all, I had run point to point osu_latency test in two nodes for 200 times. Followings are the average time in microsecond for various size of the messages - 1KB 84.8514 us 2KB 73.52535 us 4KB 272.55275 us 8KB 234.86385 us 16KB 288.88 us 32KB 523.3725 us 64KB 910.4025 us