> > > > 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.
OK, now I get it. It's an obfuscated way of writing: simple_allowed = (offloads & ~RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE) == 0 Suggest updating for readability next time that code is touched. The comment "only fast free is allowed" [1] didn't help me either; I interpreted it as "it's only allowed when fast free is set". Now that I understand the code, I can also interpret the comment as intended. [1]: https://elixir.bootlin.com/dpdk/v25.11/source/drivers/net/intel/i40e/i40e_rxtx.c#L3502 Thanks for clarifying, Bruce!
