[Intel-wired-lan] [E1000-devel] i40e card Tx resets

zhuyj zyjzyj2000 at gmail.com
Fri Mar 18 11:08:16 UTC 2016

On 03/18/2016 03:28 AM, Jesse Brandeburg wrote:
> On Thu, 17 Mar 2016 14:56:14 -0400
> Sowmini Varadhan <sowmini.varadhan at oracle.com> wrote:
>> On (03/17/16 10:20), zhuyj wrote:
>>> 1. modprobe NET_PKTGEN
>>> 2. download the tar file and uncompress to any directory.
>>> This tar file is from kernel. It is in samples/pktgen/
>>> 3. cd pktgen
>>> 4. pktgen_sample02_multiqueue.sh -i ethx -s size -t cpu_number
>> Indeed, I see the same thing as you, and it was very easy to
>> reproduce. It was very interesting that the problem can happen with
>> as few as 3 threads, at which point I see the TX hang at exactly
>> -s 12305
> Okay, sorry I hadn't jumped into this thread yet.
> I can uniquivically tell you that what Sowmini saw with the MDD with
> stack based RDS-STRESS testing is *NOT* the same as what you're seeing
> while using pktgen with invalid huge skb->data buffers.
> We can ask on netdev if the driver should defend against this kind of
> input to hard_start_xmit (transmit routine), but the driver doesn't
> check the maximum length of the skb to see if it is invalid, because
> the stack can never build (only pktgen can) these invalid SKBs.
> The issue is that pktgen builds skb->data with a contiguous buffer of
> whatever size transmit requested, (regardless of MTU) and then sends it
> straight to the transmit routine, no segmentation flags, no MSS set.
> This causes the driver to build a transmit descriptor with an invalid
> length, which the hardware then "ASSERTS" on by issuing an MDD
> interrupt and freezing the bad acting queue.
>> I see:
>> i40e 0000:82:00.0: TX driver issue detected, PF reset issued
>> i40e 0000:82:00.0 eth2: VSI_seid 390, Hung TX queue 0, tx_pending: 492, NTC:0x140, HWB: 0x140, NTU: 0x12c, TAIL: 0x12c
>> I think the common factor in both our test cases is that we have some
>> kernel thread that can efficiently send packets without any context
>> switches.
> You've found a red herring (mistakenly connected two separate events)
> so I think you can stop going down this path (pktgen).
>> Has anyone here seen this before? I'll see if I can find some cycles
>> to figure this out, if not, maybe its worth bringing up on netdev,
>> to see if others have seen this, and to draw some patterns.
> we don't need to bring it up on netdev.  We have a way to troubleshoot
> MDDs that I can send to you, if you want to do the work.  Otherwise we
> need to have some time to reproduce here.
>>> If size is set to a big number, the similar defect will occur.
>>> Adjust this size to a appropriate number, my defect will not occur.
>>> In the test, I found some types igb nic, such as i210, will work
>>> well no matter the size is a big number.
>>> some nic, such as 82580, it will not work well if the size is too big.
> This is mostly a combination of driver implementation and how the
> hardware handles a descriptor that is too large.  The driver *could*
> check to make sure the skb->data is never too large, but in that same
> vein, we *could* fix pktgen to never send a frame greater than MTU down
> to the driver.
Do you mean this is not a bug in nic?
And it is unnecessary to fix it?

But if a test tool makes tests like pktgen, how to handle it?

We just suggests not to make such tests?

Best Regards!
Zhu Yanjun
>>> As such, I think my problem results from the hardware and the big
>>> size triggers this problem.
>>> I hope this can help us all.
> Unfortunately Zhu's problem with pktgen is not a reproducer of
> Sowmini's problem.
> In the case of pktgen, it is a "don't do that, because it hurts" kind of
> bug. In the case of rds-stress, we need to reproduce it here and figure
> out what hardware constraint the driver is violating during set up of
> the transmit.

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