There are root complexes that are able to optimize their
performance when incoming data is multiple full cache lines.
PCI write end padding is the device's ability to pad the ending of
incoming packets (scatter) to full cache line such that the last
upstream write generated by an incoming packet will be a full cache
line.
Add a relevant entry to ib_device_cap_flags to report such capability
of an RDMA device.
Add the QP and WQ create flags:
* A QP/WQ created with a scatter end padding flag will cause
HW to pad the last upstream write generated by a packet to cache line.
User should consider several factors before activating this feature:
- In case of high CPU memory load (which may cause PCI back pressure in
turn), if a large percent of the writes are partial cache line, this
feature should be checked as an optional solution.
- This feature might reduce performance if most packets are between one
and two cache lines and PCIe throughput has reached its maximum
capacity. E.g. 65B packet from the network port will lead to 128B
write on PCIe, which may cause traffic on PCIe to reach high
throughput.
Signed-off-by: Noa Osherovich <noaos@mellanox.com>
Reviewed-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>
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