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

[Ferruh Yigit <ferruh.yigit@intel.com>]

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

> 
>> In virtual drivers we need to give a decision, if free the wrong packets and
>> increase the 'oerrors' or return packets backs to application without increasing
>> the 'oerrors', so that application can try to do something with packets or free
>> them increasing 'tx_dropped'.
>>
>> @David, @Andrew, do you have a suggestion? 
>