8. Enabling Additional Functionality

8.1. Running DPDK Applications Without Root Privileges

In order to run DPDK as non-root, the following Linux filesystem objects’ permissions should be adjusted to ensure that the Linux account being used to run the DPDK application has access to them:

  • All directories which serve as hugepage mount points, for example, /dev/hugepages
  • If the HPET is to be used, /dev/hpet

When running as non-root user, there may be some additional resource limits that are imposed by the system. Specifically, the following resource limits may need to be adjusted in order to ensure normal DPDK operation:

  • RLIMIT_LOCKS (number of file locks that can be held by a process)
  • RLIMIT_NOFILE (number of open file descriptors that can be held open by a process)
  • RLIMIT_MEMLOCK (amount of pinned pages the process is allowed to have)

The above limits can usually be adjusted by editing /etc/security/limits.conf file, and rebooting.

Additionally, depending on which kernel driver is in use, the relevant resources also should be accessible by the user running the DPDK application.

For vfio-pci kernel driver, the following Linux file system objects’ permissions should be adjusted:

  • The VFIO device file, /dev/vfio/vfio
  • The directories under /dev/vfio that correspond to IOMMU group numbers of devices intended to be used by DPDK, for example, /dev/vfio/50

Note

The instructions below will allow running DPDK with igb_uio or uio_pci_generic drivers as non-root with older Linux kernel versions. However, since version 4.0, the kernel does not allow unprivileged processes to read the physical address information from the pagemaps file, making it impossible for those processes to be used by non-privileged users. In such cases, using the VFIO driver is recommended.

For igb_uio or uio_pci_generic kernel drivers, the following Linux file system objects’ permissions should be adjusted:

  • The userspace-io device files in /dev, for example, /dev/uio0, /dev/uio1, and so on

  • The userspace-io sysfs config and resource files, for example for uio0:

    /sys/class/uio/uio0/device/config
/sys/class/uio/uio0/device/resource*

8.2. Power Management and Power Saving Functionality

Enhanced Intel SpeedStep® Technology must be enabled in the platform BIOS if the power management feature of DPDK is to be used. Otherwise, the sys file folder /sys/devices/system/cpu/cpu0/cpufreq will not exist, and the CPU frequency- based power management cannot be used. Consult the relevant BIOS documentation to determine how these settings can be accessed.

For example, on some Intel reference platform BIOS variants, the path to Enhanced Intel SpeedStep® Technology is:

Advanced
  -> Processor Configuration
  -> Enhanced Intel SpeedStep\ |reg| Tech

In addition, C3 and C6 should be enabled as well for power management. The path of C3 and C6 on the same platform BIOS is:

Advanced
  -> Processor Configuration
  -> Processor C3 Advanced
  -> Processor Configuration
  -> Processor C6

8.3. Using Linux Core Isolation to Reduce Context Switches

While the threads used by a DPDK application are pinned to logical cores on the system, it is possible for the Linux scheduler to run other tasks on those cores also. To help prevent additional workloads from running on those cores, it is possible to use the isolcpus Linux kernel parameter to isolate them from the general Linux scheduler.

For example, if DPDK applications are to run on logical cores 2, 4 and 6, the following should be added to the kernel parameter list:

isolcpus=2,4,6

8.4. High Precision Event Timer (HPET) Functionality

DPDK can support the system HPET as a timer source rather than the system default timers, such as the core Time-Stamp Counter (TSC) on x86 systems. To enable HPET support in DPDK:

  1. Ensure that HPET is enabled in BIOS settings.
  2. Enable HPET_MMAP support in kernel configuration. Note that this my involve doing a kernel rebuild, as many common linux distributions do not have this setting enabled by default in their kernel builds.
  3. Enable DPDK support for HPET by using the build-time meson option use_hpet, for example, meson configure -Duse_hpet=true

For an application to use the rte_get_hpet_cycles() and rte_get_hpet_hz() API calls, and optionally to make the HPET the default time source for the rte_timer library, the rte_eal_hpet_init() API call should be called at application initialization. This API call will ensure that the HPET is accessible, returning an error to the application if it is not.

For applications that require timing APIs, but not the HPET timer specifically, it is recommended that the rte_get_timer_cycles() and rte_get_timer_hz() API calls be used instead of the HPET-specific APIs. These generic APIs can work with either TSC or HPET time sources, depending on what is requested by an application call to rte_eal_hpet_init(), if any, and on what is available on the system at runtime.