[dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic inconsistent

[Zhao1, Wei]

Hi,Wu jingjing and wenzhuo

> -----Original Message-----
> From: Zhao1, Wei
> Sent: Monday, August 1, 2016 4:58 PM
> To: 'Kyle Larose' <eomereadig at gmail.com>
> Cc: dev at dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic inconsistent
> 
> Hi, Kyle Larose
>    The core problem is i40e has no statistic of discard bytes, that means even if
> when ports are not stopped, the statistic  rx_good_bytes is consist of discard
> bytes，is that reasonable? In other words, I can just minus discard bytes
> from rx_good_bytes if I can get discard bytes number, that is much better.
> 
> -----Original Message-----
> From: Kyle Larose [mailto:eomereadig at gmail.com]
> Sent: Saturday, July 30, 2016 1:17 AM
> To: Zhao1, Wei <wei.zhao1 at intel.com>
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic inconsistent
> 
> On Fri, Jul 29, 2016 at 4:50 AM, Wei Zhao1 <wei.zhao1 at intel.com> wrote:
> > rx_good_bytes and rx_good_packets statistic is inconsistent when port
> > stopped,ipackets statistic is minus the discard packets but rx_bytes
> > statistic not.Also,i40e has no statistic of discard bytes, so we have
> > to delete discard packets item from rx_good_packets statistic.
> >
> > Fixes: 9aace75fc82e ("i40e: fix statistics")
> >
> > Signed-off-by: Wei Zhao1 <wei.zhao1 at intel.com>
> > ---
> >  drivers/net/i40e/i40e_ethdev.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/i40e/i40e_ethdev.c
> > b/drivers/net/i40e/i40e_ethdev.c index 11a5804..553dfd9 100644
> > --- a/drivers/net/i40e/i40e_ethdev.c
> > +++ b/drivers/net/i40e/i40e_ethdev.c
> > @@ -2319,8 +2319,7 @@ i40e_dev_stats_get(struct rte_eth_dev *dev,
> > struct rte_eth_stats *stats)
> >
> >         stats->ipackets = pf->main_vsi->eth_stats.rx_unicast +
> >                         pf->main_vsi->eth_stats.rx_multicast +
> > -                       pf->main_vsi->eth_stats.rx_broadcast -
> > -                       pf->main_vsi->eth_stats.rx_discards;
> > +                       pf->main_vsi->eth_stats.rx_broadcast;
> >         stats->opackets = pf->main_vsi->eth_stats.tx_unicast +
> >                         pf->main_vsi->eth_stats.tx_multicast +
> >                         pf->main_vsi->eth_stats.tx_broadcast;
> > --
> > 2.5.5
> >
> 
> Is it not worse to report a received packet when no packet was actually
> received by the upper layers under normal operations than to ensure that
> packets and  bytes are consistent when an interface is stopped? It seems like
> the first case is much more likely to occur than the second.
> 
> Are we just introducing a new issue to fix another?
> 
> How does this behaviour compare to other NICs? Does the ixgbe report
> discarded packets in its ipackets? My reading of the driver is that it does not.
> In fact, it does something interesting to deal with the
> problem:
> 
> from: http://dpdk.org/browse/dpdk/tree/drivers/net/ixgbe/ixgbe_ethdev.c
> 
> /*
> * An errata states that gprc actually counts good + missed packets:
> * Workaround to set gprc to summated queue packet receives */ hw_stats-
> >gprc = *total_qprc;
> 
> total_gprc is equal to the sum of the qprc per queue. Can we do something
> similar on the i40e instead of adding unicast, mulitcast and broadcast?


I have checked ixgbe code about  Rx statistic, in function ixgbe_read_stats_registers() we can find the rx_good_bytes and rx_good_packets statistic.
It is listed below, we  can see rx_good_packets is also just addition of Queue Packets Received Count and  not minused  discard packet number.
Is there some wrong of understanding?

for (i = 0; i < IXGBE_QUEUE_STAT_COUNTERS; i++)
{
......		
                                 *total_qprc += hw_stats->qprc[i];
		*total_qbrc += hw_stats->qbrc[i];
......
}