10. Enabling Additional Functionality
10.1. Running DPDK Applications Without Root Privileges
The following sections describe generic requirements and configuration for running DPDK applications as non-root. There may be additional requirements documented for some drivers.
Hugepages must be reserved as root before running the application as non-root, for example:
sudo dpdk-hugepages.py --reserve 1G
If multi-process is not required, running with
bypasses the need to access hugepage mount point and files within it.
Otherwise, hugepage directory must be made accessible
for writing to the unprivileged user.
A good way for managing multiple applications using hugepages
is to mount the filesystem with group permissions
and add a supplementary group to each application or container.
One option is to use the script provided by this project:
export HUGEDIR=$HOME/huge-1G mkdir -p $HUGEDIR sudo dpdk-hugepages.py --mount --directory $HUGEDIR --user `id -u` --group `id -g`
In production environment, the OS can manage mount points (systemd example).
hugetlb filesystem has additional options to guarantee or limit
the amount of memory that is possible to allocate using the mount point.
Refer to the documentation.
vfio-pci kernel driver, if applicable, can eliminate the need
for physical addresses and therefore eliminate the permission requirements
If the driver requires using physical addresses (PA), the executable file must be granted additional capabilities:
IPC_LOCKto lock hugepages in memory
setcap cap_ipc_lock,cap_sys_admin+ep <executable>
If physical addresses are not accessible, the following message will appear during EAL initialization:
EAL: rte_mem_virt2phy(): cannot open /proc/self/pagemap: Permission denied
It is harmless in case PA are not needed.
10.1.2. Resource Limits
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.
See Hugepage Mapping section to learn how these limits affect EAL.
10.1.3. Device Control
If the HPET is to be used,
/dev/hpet permissions must be adjusted.
vfio-pci kernel driver, the following Linux file system objects’
permissions should be adjusted:
- The VFIO device file,
- The directories under
/dev/vfiothat correspond to IOMMU group numbers of devices intended to be used by DPDK, for example,
10.2. 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
10.3. 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.
To help prevent additional workloads, timers, RCU processing and IRQs
from running on those cores, it is possible to use
the Linux kernel parameters
to isolate them from the general Linux scheduler tasks.
For example, if a given CPU has 0-7 cores and 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 nohz_full=2,4,6 irqaffinity=0,1,3,5,7
10.4. 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:
- Ensure that HPET is enabled in BIOS settings.
HPET_MMAPsupport 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.
- 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_hz() API calls,
and optionally to make the HPET the default time source for the rte_timer library,
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
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
if any, and on what is available on the system at runtime.