Re: [PATCH 1/1] net/i40e: unset vector flag when scalar path is chosen

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Dec 17, 2025 at 03:18:42PM +0000, Loftus, Ciara wrote:
> > Subject: Re: [PATCH 1/1] net/i40e: unset vector flag when scalar path is
> > chosen
> > 
> > On Wed, Dec 17, 2025 at 02:54:36PM +0000, Ciara Loftus wrote:
> > > The tx_vec_allowed flag should be set to false if a scalar Tx path is
> > > chosen.
> > >
> > > Fixes: 1ff08bb7ad90 ("net/i40e: use common Tx path selection
> > infrastructure")
> > >
> > > Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
> > > ---
> > >  drivers/net/intel/i40e/i40e_rxtx.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/net/intel/i40e/i40e_rxtx.c
> > b/drivers/net/intel/i40e/i40e_rxtx.c
> > > index 2db58c6b24..dd859bda4e 100644
> > > --- a/drivers/net/intel/i40e/i40e_rxtx.c
> > > +++ b/drivers/net/intel/i40e/i40e_rxtx.c
> > > @@ -3631,6 +3631,9 @@ i40e_set_tx_function(struct rte_eth_dev *dev)
> > >  			ad->tx_func_type == I40E_TX_ALTIVEC ||
> > >  			ad->tx_func_type == I40E_TX_AVX2)
> > >  		dev->recycle_tx_mbufs_reuse =
> > i40e_recycle_tx_mbufs_reuse_vec;
> > > +
> > > +	if (i40e_tx_path_infos[ad->tx_func_type].features.simd_width <
> > RTE_VECT_SIMD_128)
> > > +		ad->tx_vec_allowed = false;
> > >  }
> > >
> > Under what circumstances would this be a problem, or under what
> > circumstances would we have this situaion?
> 
> The circumstances we would have this situation is when the driver
> determines that tx vectorisation is allowed but we end up selecting
> a scalar path. The result would be "vector_tx" being set for the txq
> during tx_queue_start and later during tx_queue_stop, the wrong
> path being taken in ci_txq_release_all_mbufs
> 
Would this be better fixed by some refactoring to chose the release
function based on ad->tx_func_type, rather than having a separate vector
flag?

If not, may I suggest that you remove the if condition, and just do:
	ad->tx_vec_allowed = 
		(i40e_tx_path_infos[ad->tx_func_type].features.simd_width < RTE_VECT_SIMD_128);