mlxsw: pci: Use page pool for Rx buffers allocation

mlxsw: pci: Use page pool for Rx buffers allocation

As part of driver init, all Rx queues are filled with buffers for
hardware usage. Later, when a packet is received, a new buffer should be
allocated to be used by hardware instead of the received buffer.
Packet's processing time includes allocation time, which can be improved
using page pool.

Using page pool, DMA mapping is done only for first allocation of buffers.
As subsequent buffers allocation avoid DMA mapping, it results in
performance improvement. The purpose of page pool is to allocate pages fast
from cache without locking. This lockless guarantee naturally comes from
running under a NAPI.

Use page pool to allocate the data buffer only, so hardware will use it to
fill the packet. At completion time, attach the data buffer (now filled
with packet payload) to new SKB which is allocated around the received
buffer. SKB building at completion time prevents cache miss for each
packet, as now the SKB is allocated right before packets will be handled by
networking stack.

Page pool for each Rx queue enhances Rx side performance by reclaiming
buffers back to each queue specific pool. This change significantly
improves driver performance, CPU can handle about 345% of the packets per
second it previously handled.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/1cf788a8f43c70aae6d526018ef77becb27ad6d3.1718709196.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>