> From: Morten Brørup [mailto:[email protected]] > Sent: Wednesday, 5 November 2025 12.28 > > Updated the comment preceding the 'rearm_data' fields to reflect that > some > ethdev drivers don't really set the rearm_data fields on RX descriptor > rearm, but rather when pulling the packet from the descriptor. > By doing this, they avoid a store operation into the mbuf when they > rearm > the TX descriptor, and instead postpone it to later, where it will be
Typo: TX descriptor -> RX descriptor. > combined with other store operations into the mbuf. > > Updated the comment describing what the second cache line is used for, > to > reflect that there are exceptions, where some fields are set on RX too. > > Updated comments describing what needs to be updated when adding new RX > and TX offload flags. > > Signed-off-by: Morten Brørup <[email protected]> > --- > lib/mbuf/rte_mbuf_core.h | 29 ++++++++++++++++++++++------- > 1 file changed, 22 insertions(+), 7 deletions(-) > > diff --git a/lib/mbuf/rte_mbuf_core.h b/lib/mbuf/rte_mbuf_core.h > index a9caaf4e14..6d66eab11d 100644 > --- a/lib/mbuf/rte_mbuf_core.h > +++ b/lib/mbuf/rte_mbuf_core.h > @@ -37,8 +37,8 @@ extern "C" { > * added to the right of the previously defined flags i.e. they > should count > * downwards, not upwards. > * > - * Keep these flags synchronized with rte_get_rx_ol_flag_name() and > - * rte_get_tx_ol_flag_name(). > + * Keep these flags synchronized with rte_get_rx_ol_flag_name(), > rte_get_rx_ol_flag_list(), > + * rte_get_tx_ol_flag_name(), and rte_get_tx_ol_flag_list(). > */ > > /** > @@ -180,12 +180,20 @@ extern "C" { > #define RTE_MBUF_F_RX_OUTER_L4_CKSUM_GOOD (1ULL << 22) > #define RTE_MBUF_F_RX_OUTER_L4_CKSUM_INVALID ((1ULL << 21) | (1ULL > << 22)) > > -/* add new RX flags here, don't forget to update RTE_MBUF_F_FIRST_FREE > */ > +/* > + * Add new RX flags here. > + * Don't forget to update RTE_MBUF_F_FIRST_FREE, > + * rte_get_rx_ol_flag_name(), and rte_get_rx_ol_flag_list(). > + */ > > #define RTE_MBUF_F_FIRST_FREE (1ULL << 23) > #define RTE_MBUF_F_LAST_FREE (1ULL << 40) > > -/* add new TX flags here, don't forget to update RTE_MBUF_F_LAST_FREE > */ > +/* > + * Add new TX flags here. > + * Don't forget to update RTE_MBUF_F_LAST_FREE, > RTE_MBUF_F_TX_OFFLOAD_MASK, > + * rte_get_tx_ol_flag_name(), and rte_get_tx_ol_flag_list(). > + */ > > /** > * Outer UDP checksum offload flag. This flag is used for enabling > @@ -485,7 +493,10 @@ struct __rte_cache_aligned rte_mbuf { > struct rte_mbuf *next; > #endif > > - /* next 8 bytes are initialised on RX descriptor rearm */ > + /* > + * Next 8 bytes are initialised on RX descriptor rearm, > + * or on RX when pulling packet from descriptor. > + */ > union { > uint64_t rearm_data[1]; > __extension__ > @@ -517,7 +528,7 @@ struct __rte_cache_aligned rte_mbuf { > > uint64_t ol_flags; /**< Offload features. */ > > - /* remaining 24 bytes are set on RX when pulling packet from > descriptor */ > + /* Remaining 24 bytes are set on RX when pulling packet from > descriptor. */ > union { > /* void * type of the array elements is retained for driver > compatibility. */ > void *rx_descriptor_fields1[24 / sizeof(void *)]; > @@ -603,7 +614,11 @@ struct __rte_cache_aligned rte_mbuf { > > struct rte_mempool *pool; /**< Pool from which mbuf was > allocated. */ > > - /* second cache line - fields only used in slow path or on TX */ > + /* > + * Second cache line - fields only used in slow path or on TX. > + * In special cases, some of these fields are also set on RX, > + * most notably the 'next' field is set on RX scattered packets. > + */ > #if RTE_IOVA_IN_MBUF > /** > * Next segment of scattered packet. Must be NULL in the last > -- > 2.43.0
