Re: [PATCH v3 00/9] net/mlx5: per-queue Tx rate limiting via packet pacing

Stephen Hemminger
2026-03-16T16:04:45Z

On Thu, 12 Mar 2026 23:01:11 +0100
Vincent Jardin <vjardin@free.fr> wrote:

> This series adds per-queue Tx data-rate limiting to the mlx5 PMD using
> hardware packet pacing (PP), and a symmetric rte_eth_get_queue_rate_limit()
> ethdev API to read back the configured rate.
>
> Each Tx queue can be assigned an individual rate (in Mbps) at runtime via
> rte_eth_set_queue_rate_limit(). The mlx5 implementation allocates a
> dedicated PP index per rate from the HW rate table, programs it into the
> SQ via modify_sq, and shares identical rates across queues to conserve
> table entries. A PMD-specific API exposes per-queue PP diagnostics and
> rate table capacity.
>
> Patch breakdown:
>
> 1. doc/nics/mlx5: fix stale packet pacing documentation
> 2-3. common/mlx5: query PP capabilities and extend SQ modify
> 4-6. net/mlx5: per-queue PP infrastructure, rate_limit callback,
> burst pacing devargs (tx_burst_bound, tx_typical_pkt_sz)
> 7. net/mlx5: testpmd command to query per-queue rate state
> 8. ethdev: add rte_eth_get_queue_rate_limit() symmetric getter
> + testpmd "show port <id> queue <id> rate" command
> 9. net/mlx5: rate table capacity query API
>
> Usage with testpmd:
> set port 0 queue 0 rate 1000
> set port 0 queue 1 rate 5000
> set port 0 queue 0 rate 0 # disable
> show port 0 queue 0 rate # generic ethdev query
> mlx5 port 0 txq 0 rate show # mlx5 PMD-specific query
>
> Changes since v2:
>
> Patch 4 (per-queue packet pacing infrastructure):
> - Folded "share pacing rate table entries across queues" into
> this patch (was a separate patch in v2)
>
> Patch 5 (support per-queue rate limiting):
> - Remove redundant queue_idx >= nb_tx_queues check (ethdev
> layer already validates before calling the PMD callback)
>
> Patch 8 (ethdev getter):
> - Add testpmd "show port <id> queue <id> rate" command
> in app/test-pmd/cmdline.c using rte_eth_get_queue_rate_limit()
> - Drop release notes (targeting 26.07, not 26.03)
> - Remove redundant queue_idx bounds check from mlx5 getter
>
> Patch 9 (rate table capacity query):
> - Use MLX5_MEM_SYS flag in mlx5_malloc() for system memory
> - Minor code style cleanups (line wrapping, cast formatting)
>
> Changes since v1:
>
> Addressed review feedback from Stephen Hemminger's AI:
>
> Patch 4 (per-queue packet pacing infrastructure):
> - Validate rate_mbps against HCA packet_pacing_min_rate and
> packet_pacing_max_rate bounds; return -ERANGE on out-of-range
> - Widen rate_kbps from uint32_t to uint64_t to prevent
> overflow on rate_mbps * 1000
> - Remove early mlx5_txq_free_pp_rate_limit() call from the
> allocator (moved to caller, see patch 5)
>
> Patch 5 (support per-queue rate limiting):
> - Fix PP index leak on modify_sq failure: allocate new PP into a
> temporary struct mlx5_txq_rate_limit; only swap into txq_ctrl->rl
> after modify_sq succeeds. On failure the old PP context stays intact.
> - Set rte_errno = -ret before returning errors from both the
> disable (tx_rate=0) and enable paths
>
> Patch 7 (testpmd command to query per-queue rate limit):
> - Fix inverted rte_eth_tx_queue_is_valid() return value check:
> was "if (rte_eth_tx_queue_is_valid(...))" (accepts invalid queues),
> changed to "if (rte_eth_tx_queue_is_valid(...) != 0)"
>
> Patch 9 (rate table capacity query, was patch 10 in v1):
> - Replace uint16_t seen[RTE_MAX_QUEUES_PER_PORT] (2 KB stack array)
> with heap-allocated mlx5_malloc(priv->txqs_n, ...) + mlx5_free()
> - Add early return when txqs == NULL || txqs_n == 0
> - Document in the API Doxygen that "used" reflects only the queried
> port's queues; other ports on the same device may also consume
> rate table entries
> - Add -ENOMEM to documented return values
>
> Hardware tested:
> - ConnectX-6 Dx (packet pacing with MLX5_DATA_RATE)
>
> Vincent Jardin (9):
> doc/nics/mlx5: fix stale packet pacing documentation
> common/mlx5: query packet pacing rate table capabilities
> common/mlx5: extend SQ modify to support rate limit update
> net/mlx5: add per-queue packet pacing infrastructure
> net/mlx5: support per-queue rate limiting
> net/mlx5: add burst pacing devargs
> net/mlx5: add testpmd command to query per-queue rate limit
> ethdev: add getter for per-queue Tx rate limit
> net/mlx5: add rate table capacity query API
>
> app/test-pmd/cmdline.c | 69 +++++++++++++
> doc/guides/nics/mlx5.rst | 125 ++++++++++++++++++------
> drivers/common/mlx5/mlx5_devx_cmds.c | 20 ++++
> drivers/common/mlx5/mlx5_devx_cmds.h | 14 ++-
> drivers/net/mlx5/mlx5.c | 46 +++++++++
> drivers/net/mlx5/mlx5.h | 13 +++
> drivers/net/mlx5/mlx5_testpmd.c | 93 ++++++++++++++++++
> drivers/net/mlx5/mlx5_tx.c | 104 +++++++++++++++++++-
> drivers/net/mlx5/mlx5_tx.h | 5 +
> drivers/net/mlx5/mlx5_txpp.c | 85 ++++++++++++++++
> drivers/net/mlx5/mlx5_txq.c | 141 +++++++++++++++++++++++++++
> drivers/net/mlx5/rte_pmd_mlx5.h | 62 ++++++++++++
> lib/ethdev/ethdev_driver.h | 7 ++
> lib/ethdev/rte_ethdev.c | 28 ++++++
> lib/ethdev/rte_ethdev.h | 24 +++++
> 15 files changed, 802 insertions(+), 33 deletions(-)
>

Only minor things left to address.

Error (1):

Patch 5 — git bisect breakage with obj->sq vs obj->sq_obj.sq. Patch 5 accesses the SQ DevX object via txq_ctrl->obj->sq, which is the hairpin union member. For non-hairpin DevX/HWS queues the correct field is obj->sq_obj.sq. Patch 7 fixes this, but patch 5 is broken as submitted — each commit needs to be independently correct for bisect. The sq_obj.sq change should be moved into patch 5.

Warnings (3):

Patch 8: mlx5_get_queue_rate_limit() doesn't bounds-check queue_idx before array access (the ethdev layer does, but the set path checks it too — inconsistent). Also missing release notes for the new ethdev API, and the new eth_dev_ops member needs ethdev maintainer agreement.
Patch 9: The "used" count is per-port but the API name suggests device-wide — consider renaming or iterating all ports on the shared context.