[openib-general] QP with large starting sequence adds latency to RDMA READ???

[Arlin Davis]

Sean Hefty wrote:

> Arlin Davis wrote:
>
>> I just noticed some RDMA read performance issues that seem to be 
>> related to the QP starting sequence number. If I set the starting 
>> sequence to 1 then all is fine but if I set it to 0x10000 then it 
>> seems to add ~40us to my 32KB RDMA read operation (polling for 
>> completions). Has anyone seen anything like this?
>
>
> Has anyone else noticed this issue?  You could try to reproduce this 
> by using the rdma_bw test and changing the PSN.
>
> - Sean
>

I added a starting PSN and RDMA READ option to the rdma_bw test and was 
able to reproduce on a PCI-E adapter with 4.6.2 firmware. I retried on a 
system with 4.7.0 and it looks like the problem is fixed. However,  I 
see nothing about this problem in the "bug fix" list in the release 
notes. Can someone at Mellanox confirm this problem with RDMA reads and 
add to release notes as a fix so it is documented somewhere?

http://www.mellanox.com/products/fw_images/fw-25208-4_7_0-release_notes.pdf

-arlin