Re: [dpdk-dev] [PATCH] app/testpmd: fix doubling of 'total TX dropped'

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Jul 16, 2019 at 03:23:03PM +0100, Ferruh Yigit wrote:
> On 7/16/2019 1:23 PM, Andrew Rybchenko wrote:
> > On 7/15/19 5:53 PM, Ferruh Yigit wrote:
> >> On 7/12/2019 9:32 AM, A.McLoughlin wrote:
> >>> The 'Accumulated forward statistics for all ports' incorrectly displayed
> >>> double the actual value for 'total_tx_dropped'. This was because 2
> >>> lines in the same function both incremented total_tx_dropped every time
> >>> a packet was dropped.  I removed one of these lines to fix this issue.
> >>>
> >>> Fixes: 53324971a14e ("app/testpmd: display/clear forwarding stats on demand")
> >>> Cc: david.marchand@redhat.com
> >>> Cc: stable@dpdk.org
> >>>
> >>> Signed-off-by: A.McLoughlin <aideen.mcloughlin@intel.com>
> >>> ---
> >>>   app/test-pmd/testpmd.c | 1 -
> >>>   1 file changed, 1 deletion(-)
> >>>
> >>> diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
> >>> index 3ed3523b7..c41bada50 100644
> >>> --- a/app/test-pmd/testpmd.c
> >>> +++ b/app/test-pmd/testpmd.c
> >>> @@ -1555,7 +1555,6 @@ fwd_stats_display(void)
> >>>   		total_recv += stats.ipackets;
> >>>   		total_xmit += stats.opackets;
> >>>   		total_rx_dropped += stats.imissed;
> >>> -		total_tx_dropped += ports_stats[pt_id].tx_dropped;
> >>>   		total_tx_dropped += stats.oerrors;
> >>>   		total_rx_nombuf  += stats.rx_nombuf;
> >>>   
> >>>
> >>
> >> Hi Aideen,
> >>
> >> Indeed 'rte_eth_stats->oerrors' and 'tx_dropped' are different values,
> >>
> >> in testpmd, 'TX-total' is taken as "total_xmit + total_tx_dropped", from this
> >> description it may be fair to say
> >> "total_tx_dropped = oerrors + tx_dropped"
> >>
> >> This is easier to see in HW devices, 'oerrors' is the packets sent to HW but HW
> >> reported failure for some reason, so these packets not transmitted to the medium.
> >> 'tx_dropped' is mostly calculated by application, driver returns packets that
> >> can't able to sent to HW, so application can re-try to send or free them and
> >> increase 'tx_dropped' counter.
> >>
> >>
> >> The problem is in the virtual drivers, the packets not able to sent are
> >> calculated as 'oerrors' and tx_burst functions returns the number of the
> >> successfully sent packets which cause application calculate remaining ones as
> >> 'tx_dropped' which cause the duplication.
> > 
> > I don't understand how it is. Tx burst returns a number of owned packets
> > (either successfully transmitted or internally dropped/freed). If it is 
> > smaller than number of packets in request, other packets are either 
> > retried or calculated as tx_dropped.
> 
> Virtual PMDs, at least the ones I checked, calculating not sent packets as
> error, also application calculates them as tx_dropped.
> 
> Like:
> https://git.dpdk.org/dpdk/tree/drivers/net/ring/rte_eth_ring.c?h=v19.08-rc1#n97
> 
That is probably incorrect to do. Virtual PMDs should behave as real ones
do as far as possible. I think we should change them to not count as errors
any that are not handled by the driver, provided those are returned to the
app.

/Bruce