[mpich-discuss] osu_latency test: why 8KB takes less time than 4KB and 2KB takes less time than 1KB?

[Abu Naser]

Hello Min,


Thanks for the clarification.  I will do the experiment.


Thanks.

Best Regards,

Abu Naser

________________________________
From: Min Si <msi at anl.gov>
Sent: Wednesday, June 20, 2018 1:39:30 PM
To: discuss at mpich.org
Subject: Re: [mpich-discuss] osu_latency test: why 8KB takes less time than 4KB and 2KB takes less time than 1KB?

Hi Abu,

I think Jeff means that you should run your experiment with more iterations in order to get a stable results.
- Increase the iteration of for loop in each execution (I think osu benchmark allows you to set it)
- Run the experiments 10 or 100 times, and take the average and standard deviation.

If you see a very small standard deviation (e.g., <=5%), then the trend is stable and you might not see such gaps.

Best regards,
Min
On 2018/06/20 12:14, Abu Naser wrote:

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 <jeff.science at gmail.com><mailto:jeff.science at gmail.com>
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 <an16e at my.fsu.edu<mailto:an16e at my.fsu.edu>> 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