Intel Processors

The AMD section describes how to configure AMD RYZEN or EPYC CPUs in case of issues running PF_RING ZC. In fact on AMD it is common to experience issues with the IOMMU due to the way application memory is provided to the network card with ZC drivers for directly moving packets with DMA.

On Intel usually everything works just out of the box. However, depending on the CPU, BIOS and kernel, it may happen to experience a similar issue on Intel CPUs.

The symptom consists of the application being unable to capture traffic, capture empty packets, or just being killed due to bad memory access. Examples:

# pfcount -i zc:enp179s0f0 -v 1
[RX][if_index=0][hash=4294967295][00:00:00:00:00:00 -> 00:00:00:00:00:00] [eth_type=0x0000] [caplen=1536][len=65531][eth_offset=0][l3_offset=14][l4_offset=0][payload_offset=0]
[RX][if_index=0][hash=4294967295][00:00:00:00:00:00 -> 00:00:00:00:00:00] [eth_type=0x0000] [caplen=1536][len=65531][eth_offset=0][l3_offset=14][l4_offset=0][payload_offset=0]

# pfcount -i zc:enp179s0f0
Killed

It is also possible to verify this by looking at dmesg for IOMMU or DMAR related messages. Example:

[232592.844165] DMAR: DRHD: handling fault status reg 202
[232592.845073] DMAR: [DMA Write NO_PASID] Request device [b3:00.0] fault addr 0xa6dd9000 [fault reason 0x05] PTE Write access is not set
[232592.846495] DMAR: [DMA Write NO_PASID] Request device [b3:00.0] fault addr 0xb3b9f000 [fault reason 0x05] PTE Write access is not set
[232592.847911] DMAR: [DMA Write NO_PASID] Request device [b3:00.0] fault addr 0xb96bd000 [fault reason 0x05] PTE Write access is not set

In order to fix this you need to disable IOMMU support.

  1. (Optional) Set ‘IOMMU’ (or VT-d / Virtualization Support) to ‘Disabled’ in the BIOS.

2. Disable intel_iommu in the GRUB boot parameters by appending ‘intel_iommu=off’ to GRUB_CMDLINE_LINUX /etc/default/grub and running ‘update-grub’ on Ubuntu or ‘grub2-mkconfig -o /boot/grub2/grub.cfg’ on CentOS.

Now you should be able to run ZC.

Common Issues

If you are running a UEFI-based system with CentOS/RHEL please note that the steps for configuring grub are a bit different. In that case you should run ‘grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg’ to update the boot laoder.