On 27/10/2015 16:39, Or Gerlitz wrote:
On 10/27/2015 11:40 AM, Sagi Grimberg wrote:
mlx4 devices (ConnectX-2, ConnectX-3) can not issue
max_sge in a single RDMA_READ request (resulting in
a completion error). Thus, expose lower max_sge_rd
to avoid this issue.
Sagi,
Hey Or,
Still, this patch is currently pure WA b/c we didn't do RCA (Root Cause
Analysis)
So from my discussions with the HW folks a RDMA_READ wqe cannot exceed
512B. The wqe control segment is 16 bytes, the rdma section is 12 bytes
(rkey + raddr) and each sge is 16 bytes so the computation is:
(512B-16B-12B)/16B = 30.
The reason is that the HW needs to fetch the rdma_read wqe on the RX
path (rdma_read response) and it has a limited buffer at that point.
Perhaps a dedicated #define for that is needed here.
I'll add that in the change log in v1.
Cheers,
Sagi.
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