[dpdk-dev] [PATCH 4/5] net/vhost: remove limit of vhost TX burst size

[Yang, Zhiyong]

Hi, Maxime:

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com]
> Sent: Wednesday, March 1, 2017 5:44 PM
> To: Yang, Zhiyong <zhiyong.yang at intel.com>; dev at dpdk.org
> Cc: yuanhan.liu at linux.intel.com
> Subject: Re: [PATCH 4/5] net/vhost: remove limit of vhost TX burst size
> 
> 
> 
> On 02/24/2017 09:48 AM, Zhiyong Yang wrote:
> > vhost removes limit of TX burst size(32 pkts) and supports to make an
> > best effort to transmit pkts.
> >
> > Cc: yuanhan.liu at linux.intel.com
> > Cc: maxime.coquelin at redhat.com
> >
> > Signed-off-by: Zhiyong Yang <zhiyong.yang at intel.com>
> > ---
> >  drivers/net/vhost/rte_eth_vhost.c | 24 ++++++++++++++++++++++--
> >  1 file changed, 22 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/vhost/rte_eth_vhost.c
> > b/drivers/net/vhost/rte_eth_vhost.c
> > index e98cffd..1e1fa34 100644
> > --- a/drivers/net/vhost/rte_eth_vhost.c
> > +++ b/drivers/net/vhost/rte_eth_vhost.c
> > @@ -52,6 +52,7 @@
> >  #define ETH_VHOST_QUEUES_ARG		"queues"
> >  #define ETH_VHOST_CLIENT_ARG		"client"
> >  #define ETH_VHOST_DEQUEUE_ZERO_COPY	"dequeue-zero-copy"
> > +#define VHOST_MAX_PKT_BURST 32
> >
> >  static const char *valid_arguments[] = {
> >  	ETH_VHOST_IFACE_ARG,
> > @@ -434,8 +435,27 @@ eth_vhost_tx(void *q, struct rte_mbuf **bufs,
> uint16_t nb_bufs)
> >  		goto out;
> >
> >  	/* Enqueue packets to guest RX queue */
> > -	nb_tx = rte_vhost_enqueue_burst(r->vid,
> > -			r->virtqueue_id, bufs, nb_bufs);
> > +	if (likely(nb_bufs <= VHOST_MAX_PKT_BURST))
> > +		nb_tx = rte_vhost_enqueue_burst(r->vid, r->virtqueue_id,
> > +						bufs, nb_bufs);
> > +	else {
> > +		uint16_t nb_send = nb_bufs;
> > +
> > +		while (nb_send) {
> > +			uint16_t nb_pkts;
> > +			uint16_t num = (uint16_t)RTE_MIN(nb_send,
> > +					VHOST_MAX_PKT_BURST);
> > +
> > +			nb_pkts = rte_vhost_enqueue_burst(r->vid,
> > +							  r->virtqueue_id,
> > +							  &bufs[nb_tx], num);
> > +
> > +			nb_tx += nb_pkts;
> > +			nb_send -= nb_pkts;
> > +			if (nb_pkts < num)
> > +				break;
> > +		}
> > +	}
> It looks like the if/else could be avoided, but maybe you did so for
> performance reason?
> If this is the case, maybe you could add a comment or at least state this in the
> commit message.

Yes, you are right.
if/else can be avoided and code will  look more clean.
I  choose performance between them. 
Comments will be added in V2 here.

Thanks
Zhiyong

> 
> Thanks,
> Maxime
> >
> >  	r->stats.pkts += nb_tx;
> >  	r->stats.missed_pkts += nb_bufs - nb_tx;
> >