RE: [PATCH] net/intel: optimize for fast-free hint

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Friday, 23 January 2026 13.09
> 
> On Fri, Jan 23, 2026 at 01:05:10PM +0100, Morten Brørup wrote:
> > I haven't looked into the details yet, but have a quick question
> inline below.
> >
> > > @@ -345,12 +345,20 @@ ci_txq_release_all_mbufs(struct ci_tx_queue
> *txq,
> > > bool use_ctx)
> > >  		return;
> > >
> > >  	if (!txq->vector_tx) {
> > > -		for (uint16_t i = 0; i < txq->nb_tx_desc; i++) {
> > > -			if (txq->sw_ring[i].mbuf != NULL) {
> >
> > You changed this loop to only operate on not-yet-cleaned descriptors.
> >
> > Here comes the first part of my question:
> > You removed the NULL check for txq->sw_ring[i].mbuf, thereby assuming
> that it is never NULL for not-yet-cleaned descriptors.
> >
> 
> Good point, I was quite focused on making this block and the vector
> block
> the same, I forgot that we can have NULL pointers for context
> descriptors.
> That was a silly mistake (and AI never caught it for me either.)
> 
> > > +		/* Free mbufs from (last_desc_cleaned + 1) to (tx_tail -
> > > 1). */
> > > +		const uint16_t start = (txq->last_desc_cleaned + 1) % txq-
> > > >nb_tx_desc;
> > > +		const uint16_t nb_desc = txq->nb_tx_desc;
> > > +		const uint16_t end = txq->tx_tail;
> > > +
> > > +		uint16_t i = start;

Suggest getting rid of "start"; it is only used for initializing "i".

> > > +		if (end < i) {
> > > +			for (; i < nb_desc; i++)
> > >  				rte_pktmbuf_free_seg(txq->sw_ring[i].mbuf);
> > > -				txq->sw_ring[i].mbuf = NULL;
> > > -			}
> > > +			i = 0;
> > >  		}
> > > +		for (; i < end; i++)
> > > +			rte_pktmbuf_free_seg(txq->sw_ring[i].mbuf);
> > > +		memset(txq->sw_ring, 0, sizeof(txq->sw_ring[0]) * nb_desc);

Consider also splitting this memset() into two, one for each of the two for loops.
Then you might need to keep "start" and make it non-const. :-)

> > >  		return;
> > >  	}

Or just keep the original version, looping over all descriptors.