From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH 2/2] virtio: clean up space checks on xmit
Date: Sat, 5 Dec 2015 11:50:07 -0800
Message-ID: <20151205115007.2230a16a@xeon-e3>
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To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
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	int error;
> >  
> > @@ -846,58 +845,49 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
> >  	if (likely(nb_used > txvq->vq_nentries - txvq->vq_free_thresh))
> >  		virtio_xmit_cleanup(txvq, nb_used);
> >  
> > -	nb_tx = 0;
> > -
> > -	while (nb_tx < nb_pkts) {
> > +	for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
> > +		struct rte_mbuf *txm = tx_pkts[nb_tx];
> >  		/* Need one more descriptor for virtio header. */
> > -		int need = tx_pkts[nb_tx]->nb_segs - txvq->vq_free_cnt + 1;
> > +		int need = txm->nb_segs - txvq->vq_free_cnt + 1;
> 
> While reviewing the code, I found the var name `need' is not properly
> taken. Maybe `need_cleanup' is better, and it's better to be defined
> as bool type. What do you think of that?

The variable need indicates how many more buffers are needed to
complete the transmit.  In later patches, there is a variable slots
so:
  needed = slots - free

So if needed is positive, then more buffers are needed than available
and transmit is blocked. If needed is negative then there is free
space available.

> 
> (And yes, it has nothing to do with your patch, I just found it we
> can rename it to a better name to improve the code readability a bit.
> If you agree, would you submit a patch, or should I do it?)
> 
> >  
> > -		/*Positive value indicates it need free vring descriptors */
> > +		/* Positive value indicates it need free vring descriptors */
> >  		if (unlikely(need > 0)) {
> >  			nb_used = VIRTQUEUE_NUSED(txvq);
> >  			virtio_rmb();
> >  			need = RTE_MIN(need, (int)nb_used);
> >  
> >  			virtio_xmit_cleanup(txvq, need);
> > -			need = (int)tx_pkts[nb_tx]->nb_segs -
> > -				txvq->vq_free_cnt + 1;
> > +			need = txm->nb_segs - txvq->vq_free_cnt + 1;
> > +			if (unlikely(need > 0)) {
> > +				PMD_TX_LOG(ERR,
> > +					   "No free tx descriptors to transmit");
> > +				break;
> > + 			}
>    ^
> 
> Minor nit: I found a leading white space there.

Hmm. I didn't see it in checkpatch.