Re: [dpdk-dev] x552 transmit issue and rte_ethtool - rte_ethtool_get_regs()

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Mike,

> Konstantin,
> 
> The recommended use of rte_eth_tx_prepare() had no effect, which after looking at it, makes sense. We are using "large" mbufs to support
> Jumbo frames, so nb-seg will always == 1. Additionally, we are not currently leveraging any HW offload capabilities. As such,
> rte_eth_tx_prepare() always returns "num-frames".
> 
> Taking this a step further, I have reproduced the problem using a simple c-unit test that builds bursts of frames, where each burst contains a
> max-burst of frames (32 in our application), where the interleaved frames have either a legal frame length (124-bytes) or intentionally a runt
> frame length (20-bytes++). These are dumb-simple L2 frames, i.e. NOT ip-frames. The NIC is setup to pad and append, so it should just do
> that without issue as needed. The test repeats this burst sequence a 100 times, resulting in 3200 frames attempting to be transmitted. Run
> to run, I am seeing anywhere from 750 to 3000 frames get transmitted. Thereafter, the NIC will no longer accept frames for transmit. Using
> GDB, we have confirmed the same DD status problem is present and preventing ixgbe_tx_free_bufs() from doing any actual freeing of
> resources.
> 
> Is there a minimum runt size officially supported by DPDK and/or Intel on the x550 NIC family? We could certainly do a simple frame-length
> check and discard accordingly. However, we have seen 3rd party applications send us runts, e.g. 40-byte ARP requests, over vhost-user and
> tap interfaces, so we are a bit hesitant to blindly enforce this at 60 bytes (min ETH minus CRC).

AFAIK, sending frames smaller then 64B shouldn't cause a problem.
At least I never hit such limitation.
Qi, Wenzhuo - did you ever see such issue?
My suggestion would be to open a new Bugzilla ticket for investigation and 
attach pcap file (or some scapy script to generate it) so it could be reproduced with test-pmd.
Thanks
Konstantin  


> 
> -Mike
> 
> -----Original Message-----
> From: Bly, Mike
> Sent: Tuesday, July 23, 2019 10:08 AM
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; 'dev@dpdk.org' <dev@dpdk.org>
> Subject: RE: [dpdk-dev] x552 transmit issue and rte_ethtool - rte_ethtool_get_regs()
> 
> Konstantin,
> 
> Thank you for the prompt reply on this posting. In looking at the single use-case in test-pmd's csumonly.c, it would seem prepare +
> retry_enabled may have some shortcomings as currently coded when nb_prep < nb_rx. Has anyone looked at this? I happened to notice this
> when looking for a reference for how it is expected to be used. It would seem nb_rx should be replaced with nb_prep in the retry code. I
> think the rest of the code should "just work" from there. Thoughts?
> 
> Regards,
> Mike
> 
> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> Sent: Tuesday, July 23, 2019 9:03 AM
> To: Bly, Mike <mbly@ciena.com>; 'dev@dpdk.org' <dev@dpdk.org>
> Subject: [**EXTERNAL**] RE: [dpdk-dev] x552 transmit issue and rte_ethtool - rte_ethtool_get_regs()
> 
> 
> 
> 
> >
> > Hello,
> >
> > We are chasing an interesting NIC transmit issue where after some
> > period of time with normal operation the NIC enters a state where it
> > refuses to transmit frames from our DPDK application via rte_eth_tx_burst(). All indications are the port is up and otherwise operational
> and is still receiving traffic. It simply refuses to transmit anymore.
> >
> > Our application is running DPDK 17.05.1. In digging through the email
> > archives, this appears to be related to the following posts, as we see the same nb_free = 0 and IXGBE_ADVTXD_STAT_DD not set
> problems they describe:
> > http://mails.dpdk.org/archives/dev/2017-August/073240.html
> > http://inbox.dpdk.org/dev/b704af91-dcc6-4481-a54c-3e174b744d17.h.liu@a
> > libaba-inc.com/
> >
> > Having not seen any resolution on the above DPDK posts and after a
> > number of other investigative steps, we incorporated the rte_ethtool
> > lib to provide the ability to dump the NIC register set via
> > rte_ethtool_get_regs() in the hopes that perhaps there would be something there in a status register to point us in the right direction. The
> question now is what is the best way to check the register contents dumped to the binary output file this API creates, for the x552 NIC?
> Does anyone know if a decoder script exists?
> >
> > Other ideas to pursue?
> 
> It is hard to tell without any other information, but sometimes that happens when user tries to TX malformed packet.
> Might be worth to try using rte_eth_tx_prepare() inside your app.
> It does some sanity checks to prevent such situations, especially when RTE_LIBRTE_ETHDEV_DEBUG is on.
> Konstantin
> 
> 
>