On Wed, Jan 14, 2026 at 07:05:44PM +0100, Morten Brørup wrote: > > From: Bruce Richardson [mailto:[email protected]] > > Sent: Wednesday, 14 January 2026 17.36 > > > > On Wed, Jan 14, 2026 at 04:31:31PM +0100, Morten Brørup wrote: > > > > > If I'm not mistaken, the mbuf library is not a barrier for fast- > > > > freeing > > > > > segmented packet mbufs, and thus fast-free of jumbo frames is > > > > possible. > > > > > > > > > > We need a driver developer to confirm that my suggested approach > > - > > > > > resetting the mbuf fields, incl. 'm->nb_segs' and 'm->next', when > > > > > preparing the Tx descriptor - is viable. > > > > > > > > > Excellent analysis, Morten. If I get a chance some time this > > release > > > > cycle, > > > > I will try implementing this change in our drivers, see if any > > > > difference > > > > is made. > > > > > > Bruce, > > > > > > Have you had a chance to look into the driver change requirements? > > > If not, could you please try scratching the surface, to build a gut > > feeling. > > > > I'll try and take a look this week. Juggling a few things at the > > moment, so > > I had forgotten about this. Sorry. > > > > More comments inline below. > > > > /Bruce > > > > > > > > I wonder if the vector implementations have strong requirements that > > packets are not segmented... > > > > > > The i40 driver only sets "tx_simple_allowed" and "tx_vec_allowed" > > flags when MBUF_FAST_FREE is set: > > > > > https://elixir.bootlin.com/dpdk/v25.11/source/drivers/net/intel/i40e/i4 > > 0e_rxtx.c#L3502 > > > > > > > Actually, it allows but does not require FAST_FREE. The check is just > > verifying that the flags with everything *but* FAST_FREE masked out is > > the > > same as the original flags, i.e. FAST_FREE is just ignored. > > That's not how I read the code: > ad->tx_simple_allowed = > (txq->offloads == > (txq->offloads & RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE) && > txq->tx_rs_thresh >= I40E_TX_MAX_BURST); > > Look at it with offloads=(MULTI_SEGS|FAST_FREE): > simple_allowed = (MULTI_SEGS|FAST_FREE) == (MULTI_SEGS|FAST_FREE) & FAST_FREE > i.e.: > simple_allowed = (MULTI_SEGS|FAST_FREE) == FAST_FREE > i.e.: false >
Which is correct. The only flag allowed is FAST_FREE, but its not required. If the input flags were just MULTI_SEGS, it would end up as: simple_allowed = (MULTI_SEGS) == 0 i.e. also false So the FAST_FREE flag does not affect the result. /Bruce
