> From: Bruce Richardson [mailto:bruce.richard...@intel.com] > Sent: Thursday, 3 July 2025 17.21 > > On Thu, Jul 03, 2025 at 05:12:46PM +0200, Morten Brørup wrote: > > > From: Bruce Richardson [mailto:bruce.richard...@intel.com] > > > Sent: Thursday, 3 July 2025 16.14 > > > > > > On Thu, Jul 03, 2025 at 03:59:14PM +0200, Morten Brørup wrote: > > > > For TX mbuf fast release offload, I propose to add the mbuf > mempool > > > > pointer to the ethdev tx queue configuration structure, > > > > so the ethdev TX burst operation doesn't need to fetch it from the > > > > first mbuf of each burst being fast free'd to the mempool. > > > > > > > > This modification of the struct rte_eth_txconf, and the > requirement > > > > to set the mempool pointer if the > RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE > > > > flag is set, will be an API+ABI change in 25.11. > > > > Should it be announced in the 25.07 release notes? > > > > > > > > Note: We could phase it in softly by letting the ethdev drivers > > > > check if the pointer has been set, and fall back to fetching it > > > > from mbuf[0] if not. > > > > > > > > /** > > > > * A structure used to configure a Tx ring of an Ethernet port. > > > > */ > > > > struct rte_eth_txconf { > > > > struct rte_eth_thresh tx_thresh; /**< Tx ring threshold > registers. > > > */ > > > > uint16_t tx_rs_thresh; /**< Drives the setting of RS bit on > TXDs. > > > */ > > > > uint16_t tx_free_thresh; /**< Start freeing Tx buffers if > there > > > are > > > > less free descriptors than this > value. */ > > > > > > > > uint8_t tx_deferred_start; /**< Do not start queue with > > > rte_eth_dev_start(). */ > > > > /** > > > > * Per-queue Tx offloads to be set using > RTE_ETH_TX_OFFLOAD_* > > > flags. > > > > * Only offloads set on tx_queue_offload_capa or > tx_offload_capa > > > > * fields on rte_eth_dev_info structure are allowed to be > set. > > > > */ > > > > uint64_t offloads; > > > > > > > > + /** > > > > + * Per-queue mempool to release the mbufs to; required for > > > > + * RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE offload. > > > > + */ > > > > + struct rte_mempool *mp; > > > > + > > > > > > Is this really best put in the txconf struct? Would it not be better > > > just > > > stored in the queue structure on free or Tx of the first packet? > That > > > would > > > make it not change the ABI. > > > > It seems natural to me to specify the mempool at configuration time, > > because it is a configuration parameter. > > The txconf struct seemed like the best place to put it. > > > > Fetching it from the first mbuf of each burst at runtime, and possibly > caching it, seems like a workaround for the missing configuration > parameter. > > > Not suggesting from each burst, just the first mbuf seen. One time only.
That's what I meant by "possibly caching it". :-) The check for the one-time cache update still takes up code space in the per-burst fast path. (Although very little.) But I still prefer providing configuration information at configuration time, rather than snooping it at runtime. > > /Bruce
