[Patch v2] net/mana: use rte_pktmbuf_alloc_bulk for allocating RX WQEs

[Long Li]

> Can you please quantify the performance improvement (as percentage), this
> clarifies the impact of the modification.

I didn't see any meaningful performance improvements in benchmarks. However, this should improve CPU cycles and reduce potential locking conflicts in real-world applications. 

Using batch allocation was one of the review comments during initial driver submission, suggested by Stephen Hemminger. I promised to fix it at that time. Sorry it took a while to submit this patch.

> 
> <...>
> 
> > @@ -121,19 +115,32 @@ mana_alloc_and_post_rx_wqe(struct mana_rxq
> *rxq)
> >   * Post work requests for a Rx queue.
> >   */
> >  static int
> > -mana_alloc_and_post_rx_wqes(struct mana_rxq *rxq)
> > +mana_alloc_and_post_rx_wqes(struct mana_rxq *rxq, uint32_t count)
> >  {
> >  	int ret;
> >  	uint32_t i;
> > +	struct rte_mbuf **mbufs;
> > +
> > +	mbufs = rte_calloc_socket("mana_rx_mbufs", count, sizeof(struct
> rte_mbuf *),
> > +				  0, rxq->mp->socket_id);
> > +	if (!mbufs)
> > +		return -ENOMEM;
> >
> 
> 'mbufs' is temporarily storage for allocated mbuf pointers, why not allocate if from
> stack instead, can be faster and easier to manage:
> "struct rte_mbuf *mbufs[count]"
> 
> 
> > +
> > +	ret = rte_pktmbuf_alloc_bulk(rxq->mp, mbufs, count);
> > +	if (ret) {
> > +		DP_LOG(ERR, "failed to allocate mbufs for RX");
> > +		rxq->stats.nombuf += count;
> > +		goto fail;
> > +	}
> >
> >  #ifdef RTE_ARCH_32
> >  	rxq->wqe_cnt_to_short_db = 0;
> >  #endif
> > -	for (i = 0; i < rxq->num_desc; i++) {
> > -		ret = mana_alloc_and_post_rx_wqe(rxq);
> > +	for (i = 0; i < count; i++) {
> > +		ret = mana_post_rx_wqe(rxq, mbufs[i]);
> >  		if (ret) {
> >  			DP_LOG(ERR, "failed to post RX ret = %d", ret);
> > -			return ret;
> > +			goto fail;
> >
> 
> This may leak memory. There are allocated mbufs, if exit from loop here and free
> 'mubfs' variable, how remaining mubfs will be freed?

Mbufs are always freed after fail:

fail:
        rte_free(mbufs);

>