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Support for ENA NETMAP Tx

Authored by on Oct 8 2019, 8:24 AM.



Two new tables are added to ena_tx_buffer structure:

  • netmap_map_seg stores DMA mapping structures,
  • netmap_buf_idx stores buff indexes taken from the slots.

When Tx resources are being set, the new mapping structures are created
and netmap Tx rings are being reset.

When Tx resources are being released, used netmap bufs are unmapped from
DMA and then mapping structures are destroyed.

When Tx interrupt occurrs, ena_netmap_tx_irq is called.

ena_netmap_txsync callback signalizes that there are new packets which
should be transmitted.
First, it fills ena_netmap_ctx. Then it performs two actions:

  • ena_netmap_tx_frames moves packets from netmap ring to NIC,
  • ena_netmap_tx_cleanup restores buffers from NIC and gives them back

to the userspace app.
0 is returned in case of Tx error that could be handled by the driver.

ena_netmap_tx_frames checks if there are packets ready for transmission.
Then, for each of them, ena_netmap_tx_frame is called. If error occurs,
transmitting is stopped, but if the error was cause due to HW ring being
full, information about that is not propagated to the userspace app.
When all packets are ready, doorbell is written to NIC and netmap ring
state is updated.

Parsing of one packet is done by the ena_netmap_tx_frame function.
First, it checks if number of slots does not exceed NIC limit. Invalid
packets are being dropped and the error is propagated to the upper
layer. As each netmap buffer has equal size, which is typically greater
then 2KiB, there shouldn't be any packets which contain too many slots.
Then, the ena_com_tx_ctx structure is being filled. As netmap does not
support any hardware offloads, ena_com_tx_meta structure is set to zero.
After that, ena_netmap_map_slots maps all memory slots for DMA.
If the device works in the LLQ mode, the push header is being determined
by checking if the header fits within the first socket.
If so, the portion of data is being copied directly from the slot.
In other case, the data is copied to the intermediate buffer.
First slots are treated the same as as the others, because DMA mapping
has no impact on LLQ mode. Index of each netmap buffer is taken from
slot and stored in netmap_buf_idx array. In case of mapping error,
memory is unmapped and packets are put back to the netmap ring.

ena_netmap_tx_cleanup performs out of order cleanup of sent buffers.
First, req_id is taken and is validated. As validate_tx_req_id from
ena.c is specific to kernels mbuf, another implementation is provided.
Each req_id is cleaned up by ena_netmap_tx_clean_one function. Buffers
are being unmaped from DMA and put back to netmap ring. In the end,
state of netmap and NIC rings are being updated.

Submitted by: Rafal Kozik <>

Michal Krawczyk <>

Obtained from: Semihalf
Sponsored by: Amazon, Inc.

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rS FreeBSD src repository
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Event Timeline created this revision.Oct 8 2019, 8:24 AM
This revision was not accepted when it landed; it landed in state Needs Review.Thu, Oct 31, 3:59 PM
Closed by commit rS354223: Add support for ENA NETMAP Tx (authored by mw). · Explain Why
This revision was automatically updated to reflect the committed changes.