Re: [PATCH v2] net/vhost: add pmd xstats

["Yang, Zhiyong" <zhiyong.yang@intel.com>]

Hi, Yuanhan:

Thanks a lot for your comments and suggestion in so detail. I will send v3 patch
as soon as possible.

--Zhiyong

> -----Original Message-----
> From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> Sent: Sunday, September 18, 2016 9:17 PM
> To: Yang, Zhiyong <zhiyong.yang@intel.com>
> Cc: dev@dpdk.org; thomas.monjalon@6wind.com; pmatilai@redhat.com
> Subject: Re: [PATCH v2] net/vhost: add pmd xstats
> 
> On Wed, Sep 14, 2016 at 07:43:36AM +0000, Yang, Zhiyong wrote:
> > Hi, yuanhan:
> > Thanks so much for your detailed comments.
> >
> > > -----Original Message-----
> > > From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> > > Sent: Wednesday, September 14, 2016 2:20 PM
> > > To: Yang, Zhiyong <zhiyong.yang@intel.com>
> > > Cc: dev@dpdk.org; thomas.monjalon@6wind.com; pmatilai@redhat.com
> > > Subject: Re: [PATCH v2] net/vhost: add pmd xstats
> > >
> > > On Fri, Sep 09, 2016 at 04:15:27PM +0800, Zhiyong Yang wrote:
> > > > +struct vhost_xstats {
> > > > +	uint64_t stat[16];
> > > > +};
> > > > +
> > > >  struct vhost_queue {
> > > >  	int vid;
> > > >  	rte_atomic32_t allow_queuing;
> > > > @@ -85,7 +89,8 @@ struct vhost_queue {
> > > >  	uint64_t missed_pkts;
> > > >  	uint64_t rx_bytes;
> > > >  	uint64_t tx_bytes;
> > >
> > > I'd suggest to put those statistic counters to vhost_stats struct,
> > > which could simplify the xstats_reset code a bit.
> > >
> >
> > I consider this point when I define it, but those statistic counters
> > are used by pmd stats, not only by pmd xstats,  I'm not clear if  I
> > can modify those code.  If permitted, I will do it as you said.
> 
> For sure you can modify the code :) I just would suggest to do in an single
> patch, as stated before (and below).
> 
Ok. I will do that.

> > > > +	char name[RTE_ETH_VHOST_XSTATS_NAME_SIZE];
> > > > +	uint64_t offset;
> > > > +};
> > > > +
> > > > +/* [rt]_qX_ is prepended to the name string here */ static void
> > > > +vhost_dev_xstats_reset(struct rte_eth_dev *dev) {
> > > > +	struct vhost_queue *vqrx = NULL;
> > > > +	struct vhost_queue *vqtx = NULL;
> > > > +	unsigned int i = 0;
> > > > +
> > > > +	for (i = 0; i < dev->data->nb_rx_queues; i++) {
> > > > +		if (!dev->data->rx_queues[i])
> > > > +			continue;
> > > > +		vqrx = (struct vhost_queue *)dev->data->rx_queues[i];
> > >
> > > Unnecessary cast.
> > >
> > The definition of rx_queues is  void **rx_queues;
> 
> Yes, but rx_queues[i] is with type "void *", so the cast is not necessary.
> 

I'm confused if void * ptr can access a member of struct directly. Or Need
I explicitly cast it when using it?  

> > > > +		}
> > > > +	}
> > > > +	/* non-multi/broadcast, multi/broadcast, including those
> > > > +	 * that were discarded or not sent.
> > >
> > > Hmmm, I don't follow it. You may want to reword it.
> > >
> > > > from rfc2863
> > >
> > > Which section and which page?
> > >
> > The packets received are not considered "discarded", because receiving
> > packets via Memory, not by physical NIC. Mainly for the number of
> > transmit the packets
> 
> It still took me some time to understand you.
> 
> > RFC2863 page 35  ifOutUcastPkts(non-multi/broadcast)
> 
> So, by your term, unicast == non-multicast/broadcast? If so, I'd suggest to
> use term "unicast" but not something else: it just introduces confusions.
> 
You are right . non-multicast/broadcast is equal to unicast.  I agree with you
And will modify it as you say.

> And in this case, I guess you were trying to say:
> 
>     /*
>      * According to RFC 2863 section ifHCOutMulticastPkts, ... and ...,
>      * the counter "unicast", "multicast" and "broadcast" are also
>      * increased when packets are not transmitted successfully.
>      */
> 

Yes.  

> Well, you might still need reword it.
> 
> After taking a bit closer look at the code, I'd suggest to do the countings like
> following:
> 
> - introduce a help function to increase the "broadcast" or "multicast"
>   counter, say "count_multicast_broadcast(struct vhost_stats *stats, mbuf)".
> 
> - introduce a generic function to update the generic counters: this
>   function just counts those packets have been successfully transmitted
>   or received.
> 
>   It also invoke above helper function for multicast counting.
> 
>   It basically looks like the function vhost_update_packet_xstats,
>   execpt that it doesn't handle those failure packets: it will be
>   handled in following part.
> 
> - since the case "couting multicast and broadcast with failure packts"
>   only happens in the Tx side, we could do those countings only in
>   eth_vhost_tx():
> 
>     nb_tx = rte_vhost_enqueue_burst(r->vid,
> 			r->virtqueue_id, bufs, nb_bufs);
> 
>     missed = nb_bufs - nb_tx;
>     /* put above comment here */
>     if (missed) {
> 	for_each_mbuf(mbuf) {
> 	    count_multicast_broadcast(&vq->stats, mbuf);
>         }
>     }
> 
> - there is no need to update "stat[10]" (unicast), since it can be calculated
>   from other counters, meaning we could just get the right value on query.
> 
>   This could save some cycles.
> 
Ok, Your comments are detailed and clear. I will consider to remove unicast 
and modify update functions.

> Feel free to phone me if you have any doubts.
> 
> 	--yliu