Re: Question on RDMA atomic operations

On Aug 24, 2016, at 11:43 PM, Dong Young Yoon [off-list ref] wrote:

Hi,

My name is Dong Young and I am a PhD student at the University of Michigan.
Recently, we have been working on a research topic related to RDMA and had an observation where there is a race condition between RDMA atomic operations (e.g., fetch-and-add) and RDMA 1-sided writes.
We would like to verity whether what we observed is actually true (i.e., no atomicity guaranteed between RDMA atomic operation and RDMA read/write).

Hi Dong,

If you post an atomic operation followed by RDMA read/write, you need a fence between the two, because the second one might start processing before the first one has completed processing. 

In order to do that, you need to set the IBV_SEND_FENCE in the send_flags of the wr.

Is it really true? I have also contacted other fellow researchers who worked on RDMA, but they do not seem to be 100% sure on this matter.
Thank you so much in advance for your help.

Thanks,
Dong Young--
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