5. Linux Drivers
Different PMDs may require different kernel drivers in order to work properly. Depends on the PMD being used, a corresponding kernel driver should be load and bind to the network ports.
5.1. UIO
A small kernel module to set up the device, map device memory to user-space and register interrupts.
In many cases, the standard uio_pci_generic module included in the Linux kernel
can provide the uio capability. This module can be loaded using the command:
sudo modprobe uio_pci_generic
Note
uio_pci_generic module doesn’t support the creation of virtual functions.
As an alternative to the uio_pci_generic, the DPDK also includes the igb_uio
module which can be found in the kmod subdirectory referred to above. It can
be loaded as shown below:
sudo modprobe uio
sudo insmod kmod/igb_uio.ko
Note
For some devices which lack support for legacy interrupts, e.g. virtual function
(VF) devices, the igb_uio module may be needed in place of uio_pci_generic.
Note
If UEFI secure boot is enabled, the Linux kernel may disallow the use of
UIO on the system. Therefore, devices for use by DPDK should be bound to the
vfio-pci kernel module rather than igb_uio or uio_pci_generic.
For more details see Binding and Unbinding Network Ports to/from the Kernel Modules below.
Note
If the devices used for DPDK are bound to the uio_pci_generic kernel module,
please make sure that the IOMMU is disabled or passthrough. One can add
intel_iommu=off or amd_iommu=off or intel_iommu=on iommu=pt in GRUB
command line on x86_64 systems, or add iommu.passthrough=1 on aarch64 system.
Since DPDK release 1.7 onward provides VFIO support, use of UIO is optional for platforms that support using VFIO.
5.2. VFIO
A more robust and secure driver in compare to the UIO, relying on IOMMU protection.
To make use of VFIO, the vfio-pci module must be loaded:
sudo modprobe vfio-pci
Note that in order to use VFIO, your kernel must support it. VFIO kernel modules have been included in the Linux kernel since version 3.6.0 and are usually present by default, however please consult your distributions documentation to make sure that is the case.
For DMA mapping of either external memory or hugepages, VFIO interface is used.
VFIO does not support partial unmap of once mapped memory. Hence DPDK’s memory is
mapped in hugepage granularity or system page granularity. Number of DMA
mappings is limited by kernel with user locked memory limit of a process (rlimit)
for system/hugepage memory. Another per-container overall limit applicable both
for external memory and system memory was added in kernel 5.1 defined by
VFIO module parameter dma_entry_limit with a default value of 64K.
When application is out of DMA entries, these limits need to be adjusted to
increase the allowed limit.
Also, to use VFIO, both kernel and BIOS must support and be configured to use IO virtualization (such as Intel® VT-d).
Note
vfio-pci module doesn’t support the creation of virtual functions.
For proper operation of VFIO when running DPDK applications as a non-privileged user, correct permissions should also be set up. This can be done by using the DPDK setup script (called dpdk-setup.sh and located in the usertools directory).
Note
VFIO can be used without IOMMU. While this is just as unsafe as using UIO, it does make it possible for the user to keep the degree of device access and programming that VFIO has, in situations where IOMMU is not available.
5.3. Bifurcated Driver
PMDs which use the bifurcated driver co-exists with the device kernel driver. On such model the NIC is controlled by the kernel, while the data path is performed by the PMD directly on top of the device.
Such model has the following benefits:
- It is secure and robust, as the memory management and isolation is done by the kernel.
- It enables the user to use legacy linux tools such as
ethtoolorifconfigwhile running DPDK application on the same network ports.- It enables the DPDK application to filter only part of the traffic, while the rest will be directed and handled by the kernel driver. The flow bifurcation is performed by the NIC hardware. As an example, using Flow isolated mode allows to choose strictly what is received in DPDK.
More about the bifurcated driver can be found in Mellanox Bifurcated DPDK PMD.
5.4. Binding and Unbinding Network Ports to/from the Kernel Modules
Note
PMDs Which use the bifurcated driver should not be unbind from their kernel drivers. this section is for PMDs which use the UIO or VFIO drivers.
As of release 1.4, DPDK applications no longer automatically unbind all supported network ports from the kernel driver in use.
Instead, in case the PMD being used use the UIO or VFIO drivers, all ports that are to be used by a DPDK application must be bound to the
uio_pci_generic, igb_uio or vfio-pci module before the application is run.
For such PMDs, any network ports under Linux* control will be ignored and cannot be used by the application.
To bind ports to the uio_pci_generic, igb_uio or vfio-pci module for DPDK use,
and then subsequently return ports to Linux* control,
a utility script called dpdk-devbind.py is provided in the usertools subdirectory.
This utility can be used to provide a view of the current state of the network ports on the system,
and to bind and unbind those ports from the different kernel modules, including the uio and vfio modules.
The following are some examples of how the script can be used.
A full description of the script and its parameters can be obtained by calling the script with the --help or --usage options.
Note that the uio or vfio kernel modules to be used, should be loaded into the kernel before
running the dpdk-devbind.py script.
Warning
Due to the way VFIO works, there are certain limitations to which devices can be used with VFIO. Mainly it comes down to how IOMMU groups work. Any Virtual Function device can be used with VFIO on its own, but physical devices will require either all ports bound to VFIO, or some of them bound to VFIO while others not being bound to anything at all.
If your device is behind a PCI-to-PCI bridge, the bridge will then be part of the IOMMU group in which your device is in. Therefore, the bridge driver should also be unbound from the bridge PCI device for VFIO to work with devices behind the bridge.
Warning
While any user can run the dpdk-devbind.py script to view the status of the network ports, binding or unbinding network ports requires root privileges.
To see the status of all network ports on the system:
./usertools/dpdk-devbind.py --status
Network devices using DPDK-compatible driver
============================================
0000:82:00.0 '82599EB 10-GbE NIC' drv=uio_pci_generic unused=ixgbe
0000:82:00.1 '82599EB 10-GbE NIC' drv=uio_pci_generic unused=ixgbe
Network devices using kernel driver
===================================
0000:04:00.0 'I350 1-GbE NIC' if=em0 drv=igb unused=uio_pci_generic *Active*
0000:04:00.1 'I350 1-GbE NIC' if=eth1 drv=igb unused=uio_pci_generic
0000:04:00.2 'I350 1-GbE NIC' if=eth2 drv=igb unused=uio_pci_generic
0000:04:00.3 'I350 1-GbE NIC' if=eth3 drv=igb unused=uio_pci_generic
Other network devices
=====================
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To bind device eth1,``04:00.1``, to the uio_pci_generic driver:
./usertools/dpdk-devbind.py --bind=uio_pci_generic 04:00.1
or, alternatively,
./usertools/dpdk-devbind.py --bind=uio_pci_generic eth1
To restore device 82:00.0 to its original kernel binding:
./usertools/dpdk-devbind.py --bind=ixgbe 82:00.0