5630257fcc
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
160 lines
7.1 KiB
ReStructuredText
160 lines
7.1 KiB
ReStructuredText
.. SPDX-License-Identifier: BSD-3-Clause
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Copyright(c) 2010-2014 Intel Corporation.
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.. _Enabling_Additional_Functionality:
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Enabling Additional Functionality
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=================================
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.. _High_Precision_Event_Timer:
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High Precision Event Timer (HPET) Functionality
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-----------------------------------------------
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BIOS Support
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~~~~~~~~~~~~
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The High Precision Timer (HPET) must be enabled in the platform BIOS if the HPET is to be used.
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Otherwise, the Time Stamp Counter (TSC) is used by default.
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The BIOS is typically accessed by pressing F2 while the platform is starting up.
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The user can then navigate to the HPET option. On the Crystal Forest platform BIOS, the path is:
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**Advanced -> PCH-IO Configuration -> High Precision Timer ->** (Change from Disabled to Enabled if necessary).
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On a system that has already booted, the following command can be issued to check if HPET is enabled::
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grep hpet /proc/timer_list
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If no entries are returned, HPET must be enabled in the BIOS (as per the instructions above) and the system rebooted.
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Linux Kernel Support
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~~~~~~~~~~~~~~~~~~~~
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The DPDK makes use of the platform HPET timer by mapping the timer counter into the process address space, and as such,
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requires that the ``HPET_MMAP`` kernel configuration option be enabled.
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.. warning::
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On Fedora, and other common distributions such as Ubuntu, the ``HPET_MMAP`` kernel option is not enabled by default.
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To recompile the Linux kernel with this option enabled, please consult the distributions documentation for the relevant instructions.
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Enabling HPET in the DPDK
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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By default, HPET support is disabled in the DPDK build configuration files.
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To use HPET, the ``CONFIG_RTE_LIBEAL_USE_HPET`` setting should be changed to ``y``, which will enable the HPET settings at compile time.
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For an application to use the ``rte_get_hpet_cycles()`` and ``rte_get_hpet_hz()`` API calls,
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and optionally to make the HPET the default time source for the rte_timer library,
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the new ``rte_eal_hpet_init()`` API call should be called at application initialization.
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This API call will ensure that the HPET is accessible, returning an error to the application if it is not,
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for example, if ``HPET_MMAP`` is not enabled in the kernel.
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The application can then determine what action to take, if any, if the HPET is not available at run-time.
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.. note::
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For applications that require timing APIs, but not the HPET timer specifically,
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it is recommended that the ``rte_get_timer_cycles()`` and ``rte_get_timer_hz()`` API calls be used instead of the HPET-specific APIs.
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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()``,
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if any, and on what is available on the system at runtime.
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Running DPDK Applications Without Root Privileges
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--------------------------------------------------------
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.. note::
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The instructions below will allow running DPDK as non-root with older
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Linux kernel versions. However, since version 4.0, the kernel does not allow
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unprivileged processes to read the physical address information from
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the pagemaps file, making it impossible for those processes to use HW
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devices which require physical addresses
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Although applications using the DPDK use network ports and other hardware resources directly,
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with a number of small permission adjustments it is possible to run these applications as a user other than "root".
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To do so, the ownership, or permissions, on the following Linux file system objects should be adjusted to ensure that
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the Linux user account being used to run the DPDK application has access to them:
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* All directories which serve as hugepage mount points, for example, ``/mnt/huge``
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* The userspace-io device files in ``/dev``, for example, ``/dev/uio0``, ``/dev/uio1``, and so on
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* The userspace-io sysfs config and resource files, for example for ``uio0``::
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/sys/class/uio/uio0/device/config
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/sys/class/uio/uio0/device/resource*
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* If the HPET is to be used, ``/dev/hpet``
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.. note::
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On some Linux installations, ``/dev/hugepages`` is also a hugepage mount point created by default.
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Power Management and Power Saving Functionality
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-----------------------------------------------
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Enhanced Intel SpeedStep® Technology must be enabled in the platform BIOS if the power management feature of DPDK is to be used.
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Otherwise, the sys file folder ``/sys/devices/system/cpu/cpu0/cpufreq`` will not exist, and the CPU frequency- based power management cannot be used.
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Consult the relevant BIOS documentation to determine how these settings can be accessed.
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For example, on some Intel reference platform BIOS variants, the path to Enhanced Intel SpeedStep® Technology is::
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Advanced
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-> Processor Configuration
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-> Enhanced Intel SpeedStep® Tech
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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::
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Advanced
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-> Processor Configuration
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-> Processor C3 Advanced
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-> Processor Configuration
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-> Processor C6
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Using Linux Core Isolation to Reduce Context Switches
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-----------------------------------------------------
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While the threads used by an DPDK application are pinned to logical cores on the system,
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it is possible for the Linux scheduler to run other tasks on those cores also.
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To help prevent additional workloads from running on those cores,
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it is possible to use the ``isolcpus`` Linux kernel parameter to isolate them from the general Linux scheduler.
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For example, if DPDK applications are to run on logical cores 2, 4 and 6,
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the following should be added to the kernel parameter list:
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.. code-block:: console
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isolcpus=2,4,6
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Loading the DPDK KNI Kernel Module
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----------------------------------
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To run the DPDK Kernel NIC Interface (KNI) sample application, an extra kernel module (the kni module) must be loaded into the running kernel.
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The module is found in the kmod sub-directory of the DPDK target directory.
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Similar to the loading of the ``igb_uio`` module, this module should be loaded using the insmod command as shown below
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(assuming that the current directory is the DPDK target directory):
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.. code-block:: console
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insmod kmod/rte_kni.ko
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.. note::
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See the "Kernel NIC Interface Sample Application" chapter in the *DPDK Sample Applications User Guide* for more details.
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Using Linux IOMMU Pass-Through to Run DPDK with Intel® VT-d
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-----------------------------------------------------------
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To enable Intel® VT-d in a Linux kernel, a number of kernel configuration options must be set. These include:
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* ``IOMMU_SUPPORT``
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* ``IOMMU_API``
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* ``INTEL_IOMMU``
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In addition, to run the DPDK with Intel® VT-d, the ``iommu=pt`` kernel parameter must be used when using ``igb_uio`` driver.
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This results in pass-through of the DMAR (DMA Remapping) lookup in the host.
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Also, if ``INTEL_IOMMU_DEFAULT_ON`` is not set in the kernel, the ``intel_iommu=on`` kernel parameter must be used too.
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This ensures that the Intel IOMMU is being initialized as expected.
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Please note that while using ``iommu=pt`` is compulsory for ``igb_uio driver``, the ``vfio-pci`` driver can actually work with both ``iommu=pt`` and ``iommu=on``.
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