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

[Zhao1, Wei]

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?