[PATCH net v3 0/5] net: mvneta: fix the TX queue arbitration and the mqprio offload

[Josef Schlehofer]

The NETA TX arbiter is left at its reset default, which serves the TX
queues in fixed priority. Under load a busy queue starves the others.
OpenWrt has worked around this since 2017 by sending all TX traffic
of its 32-bit boards through queue 0 [1].

Patch 5 serves the queues in weighted round robin. mvpp2 also sets its
TX queues to round robin, in mvpp2_defaults_set(). An mqprio offload
keeps the fixed priority, as its traffic classes may rely on it. Without
the offload the queues are served in WRR, also when skbedit or a
software mqprio picks them.

While working on it, four older bugs in the mqprio offload showed up.
Turning the shaper off leaves the per-queue rate limits in place
(patch 1). Deleting the qdisc never reaches the driver (patch 2). A
failed setup is not undone (patch 3). Opening the interface or changing
its MTU sets every rate limit to 10.23 Mbit/s (patch 4).

The series was tested on a Turris Omnia (Armada 385). With an mqprio
offload and "queues 4@0 4@4" on a 100 Mbit/s link, one stream on queues
4 to 7 got 94 Mbit/s and three streams on queues 0 to 3 got 0.2 Mbit/s
together. The other NETA variants were not tested, but the driver
already programs registers of the same block (MVNETA_TX_MTU and the
token sizes) on all of them. Suspend and resume were not tested.

With patch 2, replacing an offloaded mqprio qdisc under a new handle
with another qdisc that sets traffic classes loses them. The new qdisc
is set up before the old one is torn down, and the driver now acts on
that teardown. The core does the same when the old qdisc is a software
mqprio. A taprio qdisc left without traffic classes sends nothing.

Changes in v3:
- Patch 5 (patch 3 in v2): keep the fixed priority while an mqprio
  offload is set up. Moved to the end of the series.
- Patch 4: braces around the loop bodies.
- Patch 2: the commit message also mentions a taprio replacement. The
  code is unchanged.
- Patches 1 to 3: Reviewed-by tags added.
- v2: https://lore.kernel.org/netdev/20261103125021.70845-1-pepe.schlehofer@xxxxxxxxx/
- v1: https://lore.kernel.org/netdev/20261102112816.12322-1-pepe.schlehofer@xxxxxxxxx/

[1] https://github.com/openwrt/openwrt/blob/a5e96c837ead549820867bb83c1ad471e39f5ace/target/linux/mvebu/patches-6.18/700-mvneta-tx-queue-workaround.patch

Josef Schlehofer (5):
  net: mvneta: lift the per-queue TX rate limits
  net: mvneta: fix the removal of the mqprio offload
  net: mvneta: unwind a failed mqprio setup
  net: mvneta: keep the TX rate limits across open and MTU change
  net: mvneta: serve the TX queues in weighted round robin

 drivers/net/ethernet/marvell/mvneta.c | 112 +++++++++++++++++++++++---
 1 file changed, 100 insertions(+), 12 deletions(-)


base-commit: f56daaadfecae1f760d0fb34385b256d3af68970
-- 
2.54.0 (Apple Git-157)