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[net80211] First part of A-MSDU offload handling - don't bump A-MPDU reordering seqno
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Authored by adrian on Jun 11 2020, 6:11 PM.

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wireless
Summary

When doing A-MSDU offload handling the driver is required to mark
A-MSDUs from the same MPDU with the same sequence number.
This allows encryption and sequence number offload to work right.

In the A-MSDU path the sequence number check looked at the
A-MSDU flags in the frame to see whether it's part of the same
seqno and will pass them (ie, not increment rx_seq until the last
A-MSDU is seen from the driver, or a new seqno shows up.)

However, I did this work in the A-MSDU path but not the A-MSDU in A-MPDU
path. Now, this requires two parts:

  • Don't bump the rx sequence number, same as above; and
  • If frames go into the reordering buffer, they need to be added into the slot as a set of frames rather than a single frame, so once a new seqno shows up that slot can be marked as "full" and we can move on.

This patch does the former. The latter requires that I find and commit
work to change rxa_m from an mbuf to an mbufq and then handle A-MSDU
there. But the former is enough in the normal case to allow
A-MSDU through.

This allows the athp driver (QCA9880) throughput to go from VERY LOW
(like 5mbit TCP, 1/3-1/4 expected UDP throughput) to ~ 250mbit TCP
and > 300mbit UDP on a VHT40 channel. TCP sucks because, well,
it shows up as MASSIVE packet loss when all but one frame in an A-MSDU
is dropped. Le whoops.

Test Plan
  • QCA9880, AP mode, talking to my macbook pro on 5GHz VHT/40; iperf

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