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

[Zhao1, Wei]

Hi, Wujingjing and Kyle Larose 



> -----Original Message-----
> From: Zhao1, Wei
> Sent: Tuesday, August 2, 2016 11:27 AM
> To: Wu, Jingjing <jingjing.wu at intel.com>; Lu, Wenzhuo
> <wenzhuo.lu at intel.com>
> Cc: dev at dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic inconsistent
> 
> 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];
> ......
> }

   The problem is i40e has no statistic of discard bytes, so it is impossible to minus discard bytes from rx_good_bytes . If you think it's not reasonable to 
Delete  rx_discards iterm from rx_good_packets statistic, this patch will be superseded. Because I didn't find other way to correct this problem at present.