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

[Kyle Larose]

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?