Re: ixgbe packet drops not accounted for

[Zoltan Kiss <zoltan.kiss@linaro.org>]

Never mind, I've digged a bit more in the sink's driver stats, it turned 
out there are a lot of RX misses when it receives through the test box. 
Increasing the RX ring from 512 to 2048 solved the issue. I guess the 
change in the burst pattern caused this whole issue.

Regards,

Zoltan

On 23/07/15 12:15, Zoltan Kiss wrote:
> Hi,
>
> I've seen an odd behaviour in my test setup, which affected my test
> results, so I set up a much simpler scenario.
> I'm using netmap pktgen as a packet source, it creates a steady 14.2
> Mpps of 64 byte UDP packets over one port of a 82599ES dual port card.
> This traffic then goes to an another similar machine with the same dual
> port NIC, where it get forwarded out on the other port. The packet sink
> runs on the same machine as the generator, it's also netmap pktgen, and
> it tells me there is a big fluctuation of throughput between 13 and 14
> Mpps, the average comes out around 13.4 Mpps. After I've stripped down
> my test app to nothing but calling rx and tx functions in a loop (it
> doesn't even modifies the MAC address as DPDK l2fwd does), I've started
> to check what rte_eth_tx_burst() tells us. I've added it's return value
> to a counter, and a separate thread printed it out every second
> (sleep(1)), and I've found it reports a steady 14.05 Mpps output. I've
> checked with rte_eth_stats_get(), it gives me the same numbers, and no
> indication of any failure.
> When I've connected the generator to the sink directly, it was able to
> receive all the packets, so it's not that the sink is not able to count
> them all. I've even replaced the cables with each other to see if the
> one towards the sink drops some packets, but nothing changed.
> I had the impression that once rte_eth_tx_burst() managed to place the
> packets on the descriptor ring, it will go out in some finite time, or
> if the card itself drops it, it will appear in the stats at least, but
> the oerrors and q_errors values are always 0.
> Does anyone has an idea where could those packets (avg 0.6 Mpps) get
> dropped?
>
> Regards,
>
> Zoltan Kiss