Re: [Intel-wired-lan] [BUG] ice: Temporary packet processing overload causes permanent RX drops

[Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>]

Am 09.12.25 um 01:05 schrieb Jacob Keller:
> On 12/5/2025 6:01 AM, Marcus Wichelmann wrote:
>> Hi there, I broke some network cards again. This time I noticed continuous RX packet drops with an Intel E810-XXV.
>>>> We have reproduced this with:
>>   Linux 6.8.0-88-generic (Ubuntu 24.04)
>>   Linux 6.14.0-36-generic (Ubuntu 24.04 HWE)
>>   Linux 6.18.0-061800-generic (Ubuntu Mainline PPA)
> 
> I think we recently merged a bunch of work on the Rx path as part of our
> conversion to page pool. It would be interesting to see if those changes
> impact this. Clearly the issue goes back some time since v6.8 at least..
Hi Jacob,

I guess you mean 93f53db9f9dc ("ice: switch to Page Pool")?

I have now repeated all tests with a kernel built from latest net-next
branch and can still reproduce it, even though I needed way higher packet
rates (15 instead of 4 Mpps when using 256 channels). Something about the
packet processing on our test system seems to have gotten way more
efficient with this kernel update.

The symptoms are the same. The following IO_PAGE_FAULTs appear in the
kernel log and after that, there is a permanent packet loss of 1-10%
even at very low packet rates.

  kernel: ice 0000:c7:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x002b address=0x4000180000 flags=0x0020]
  kernel: ice 0000:c7:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x002b address=0x4000180000 flags=0x0020]
  kernel: workqueue: drm_fb_helper_damage_work hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
  kernel: ice 0000:c7:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x002b address=0x4000180000 flags=0x0020]
  kernel: workqueue: drm_fb_helper_damage_work hogged CPU for >10000us 5 times, consider switching to WQ_UNBOUND
  kernel: ice 0000:c7:00.1: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x002c address=0x4000180000 flags=0x0020]
  [...]
  kernel: ice 0000:c7:00.1: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x002c address=0x4000180000 flags=0x0020]
  kernel: amd_iommu_report_page_fault: 10 callbacks suppressed
  [...]

I experimented with a few different channel counts and noticed that
the issue only occurs with a combined channel count >128. So on
systems with less many CPU cores, this bug probably never occurs.

  256: reproduced.
  254: reproduced.
  200: reproduced.
  129: reproduced.
  128: stable.
   64: stable.

Tested using "ethtool -L eth{0,1} combined XXX".

With <=128 channels, only the "... hogged CPU ..." warnings appear
but no IO_PAGE_FAULTs. There is also no permanent packet loss after
stopping the traffic generator.

>> [...]
>>
>> 3. Stop the traffic generator and re-run it with a way lower packet rate, e.g. 10.000 pps. Now it can be seen that
>> a good part of these packets is being dropped, even though the kernel could easily keep up with this small packet rate.
> 
> I assume the rx_dropped counter still incrementing here?

Yes. After the NIC is in this broken state, a few percent of all
packets is being dropped and the rx_dropped counter increases
with each of them.

>> [...]

I also looked into why the packet processing load on this system
is so high and `perf top` shows that it almost completely
originates from native_queued_spin_lock_slowpath.

When digging deeper using `perf lock contention -Y spinlock`:

 contended   total wait     max wait     avg wait         type   caller
   1724043      4.36 m     198.66 us    151.66 us     spinlock   __netif_receive_skb_core.constprop.0+0x832
     35960      2.51 s     112.57 ms     69.51 us     spinlock   __netif_receive_skb_core.constprop.0+0x832
       620    103.79 ms    189.87 us    167.40 us     spinlock   do_sys_poll+0x26f

I'm not yet sure what is causing this.
I don't think it's related to this issue, but maybe that's part of
what brings this bug to daylight, so probably still worth a mention.

I hope you can make some sense of all that.

Thanks,
Marcus