On 6/24/2018 9:16 PM, Sagi Grimberg wrote:
Hi Yishai,
This series from Yonatan introduces the NULL MR type and its related
verbs.
It is used to force local HCA operations to skip the PCI bus access,
while keeping
track of the processed length in the ibv_sge handling.
Meaning, instead of a PCI write access the HCA leaves the target memory
untouched, and skips filling that packet section.
Similar behavior is done upon send, the HCA skips data which is pointed
by that NULL MR and saves PCI bus access.
This functionality saves PCI read/write operations and improve
performance.
Performance of what? I read this but can't figure out what its meant to
be used for.
Hi Sagi,
We are talking on avoiding PCI bus transfers by the HCA which should
give better performance.
The expected use case from application point of view is when it does not
intend to access the data, or need data to be 0 filled, this can be
achieved by that NULL MR Type.
Please see the man page as part of this PR [1], it describes the above I
believe in a clear way.
[1]
https://github.com/linux-rdma/rdma-core/pull/351/commits/3d8d63f6ae506c9805f49e0aee2281bc2efbc849#diff-c820d86c5335dbf3afd671dfb984dbd0R33
Yishai
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