> From: fengchengwen [mailto:fengcheng...@huawei.com]
> Sent: Tuesday, 5 August 2025 04.10
>
> On 8/4/2025 3:42 AM, Morten Brørup wrote:
> > When an ethdev port is configured for fast mbuf release, the driver can
> > use a TX burst function relying on the fast mbuf release preconditions.
> > Thus, also configuring this port or a queue on the port for transmitting
> > segmented packets is prohibited.
> > Checks for these conflicting configurations have been added to the ethdev
> > library, so the drivers don't have to implement them.
>
> I think the new comment part of ombuf-fast-free and multi-seg in '[PATCH v3
> 2/3] ethdev: Improve descriptions of RX and TX offloads'
> could drop or within this commit.
Although the comments are new, I think the behavior described by the new
comments is not really new, it was just undocumented.
So, patch 2/3 properly documents it, and patch 3/3 enforces it in the ethdev
layer, so drivers don't have to.
>
> >
> > Signed-off-by: Morten Brørup <m...@smartsharesystems.com>
> > Acked-by: Bruce Richardson <bruce.richard...@intel.com>
> > Acked-by: Andrew Rybchenko <andrew.rybche...@oktetlabs.ru>
> > Acked-by: Konstantin Ananyev <konstantin.anan...@huawei.com>
> > ---
> > v3:
> > * Shorten the added log messages. (Stephen Hemminger, Ivan Malov)
> > ---
> > lib/ethdev/rte_ethdev.c | 37 +++++++++++++++++++++++++++++++++++++
> > 1 file changed, 37 insertions(+)
> >
> > diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
> > index dd7c00bc94..00afda873f 100644
> > --- a/lib/ethdev/rte_ethdev.c
> > +++ b/lib/ethdev/rte_ethdev.c
> > @@ -1531,6 +1531,18 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t
> nb_rx_q, uint16_t nb_tx_q,
> > goto rollback;
> > }
> >
> > + /* MBUF_FAST_FREE preconditions conflict with MULTI_SEGS support. */
> > + if ((dev_conf->txmode.offloads & RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE) &&
> > + (dev_conf->txmode.offloads & RTE_ETH_TX_OFFLOAD_MULTI_SEGS)) {
> > + RTE_ETHDEV_LOG_LINE(ERR,
> > + "id=%d offload clash, %s vs %s",
>
> Suggest keep the same trace fmt. e.g.: Ethdev port_id=%u
> The same below
Initial versions of the series did that, but other reviewers requested a
shorter log format.
>
> > + port_id,
> > +
> rte_eth_dev_tx_offload_name(RTE_ETH_TX_OFFLOAD_MULTI_SEGS),
> > +
> rte_eth_dev_tx_offload_name(RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE));
> > + ret = -EINVAL;
> > + goto rollback;
> > + }
> > +
> > dev->data->dev_conf.rx_adv_conf.rss_conf.rss_hf =
> > rte_eth_rss_hf_refine(dev_conf->rx_adv_conf.rss_conf.rss_hf);
> >
> > @@ -2709,6 +2721,31 @@ rte_eth_tx_queue_setup(uint16_t port_id, uint16_t
> tx_queue_id,
> > return -EINVAL;
> > }
> >
> > + /*
> > + * If the driver uses a Tx function with MBUF_FAST_FREE preconditions,
> > + * per-queue MULTI_SEGS support is not possible.
> > + */
> > + if ((dev->data->dev_conf.txmode.offloads &
> RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE) &&
> > + (local_conf.offloads & RTE_ETH_TX_OFFLOAD_MULTI_SEGS)) {
> > + RTE_ETHDEV_LOG_LINE(ERR,
> > + "id=%d txq=%d offload clash, per-queue %s vs per-port
> > %s",
> > + port_id, tx_queue_id,
> > +
> rte_eth_dev_tx_offload_name(RTE_ETH_TX_OFFLOAD_MULTI_SEGS),
> > +
> rte_eth_dev_tx_offload_name(RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE));
> > + return -EINVAL;
> > + }
> > + /*
> > + * If the driver uses a Tx function with MULTI_SEGS support,
> > + * runtime support for per-queue MBUF_FAST_FREE optimization depends on
> the driver.
> > + */
> > + if ((dev->data->dev_conf.txmode.offloads &
> RTE_ETH_TX_OFFLOAD_MULTI_SEGS) &&
> > + (local_conf.offloads &
> > RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE))
> > + RTE_ETHDEV_LOG_LINE(DEBUG,
> > + "id=%d txq=%d potential offload clash, per-queue %s vs
> per-port %s: PMD to decide",
> > + port_id, tx_queue_id,
> > +
> rte_eth_dev_tx_offload_name(RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE),
> > +
> rte_eth_dev_tx_offload_name(RTE_ETH_TX_OFFLOAD_MULTI_SEGS));
>
> 1\ The global port configuration will take effect on all queues.
> If it don't support both MBUF_FAST_FREE and MULTI_SEG, why don't ban it
> here?
There is a slight difference...
If a port is configured for MBUF_FAST_FREE, it may install a TX function
(port-wide, i.e. on all queues) relying on the mbuf-fast-free requirements,
which prohibit segmented packets. So combining per-port MBUF_FAST_FREE with
per-port or per-queue MULTI_SEGS is impossible.
However, if a port is configured for MULTI_SEGS, it may install a TX function
(port-wide) with support for per-queue MBUF_FAST_FREE, by checking the queue
structure at runtime.
> 2\ Debug level is easy to ignore, how about warning?
If a driver's installed MULTI_SEGS TX function supports runtime checking the
queue for MBUF_FAST_FREE, then there should be no warning/notice level log
message, as it is considered "normal" behavior.
However, if a driver doesn't support it, the driver must return -EINVAL for
such a queue configuration request. And if the driver doesn't log any message
with that, then this debug level log message could help the user debug the
issue.
I was in doubt if I should add this debug check or not, but I decided that it
might be useful for debugging driver issues related to such a configuration.
>
> > +
> > rte_ethdev_trace_txq_setup(port_id, tx_queue_id, nb_tx_desc, tx_conf);
> > return eth_err(port_id, dev->dev_ops->tx_queue_setup(dev,
> > tx_queue_id, nb_tx_desc, socket_id, &local_conf));
