705e197413
Documented the role of RTE_ARM_EAL_RDTSC_USE_PMU to enable PMU based rte_rdtsc(). Signed-off-by: Jerin Jacob <jerinj@marvell.com> Acked-by: Ruifeng Wang <ruifeng.wang@arm.com>
114 lines
3.6 KiB
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114 lines
3.6 KiB
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.. SPDX-License-Identifier: BSD-3-Clause
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Copyright(c) 2010-2014 Intel Corporation.
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Profile Your Application
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========================
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The following sections describe methods of profiling DPDK applications on
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different architectures.
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Profiling on x86
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----------------
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Intel processors provide performance counters to monitor events.
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Some tools provided by Intel, such as Intel® VTune™ Amplifier, can be used
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to profile and benchmark an application.
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See the *VTune Performance Analyzer Essentials* publication from Intel Press for more information.
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For a DPDK application, this can be done in a Linux* application environment only.
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The main situations that should be monitored through event counters are:
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* Cache misses
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* Branch mis-predicts
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* DTLB misses
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* Long latency instructions and exceptions
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Refer to the
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`Intel Performance Analysis Guide <http://software.intel.com/sites/products/collateral/hpc/vtune/performance_analysis_guide.pdf>`_
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for details about application profiling.
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Profiling with VTune
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~~~~~~~~~~~~~~~~~~~~
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To allow VTune attaching to the DPDK application, reconfigure a DPDK build
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folder by passing ``-Dc_args=-DRTE_ETHDEV_PROFILE_WITH_VTUNE`` meson option
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and recompile the DPDK:
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.. code-block:: console
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meson build
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meson configure build -Dc_args=-DRTE_ETHDEV_PROFILE_WITH_VTUNE
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ninja -C build
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Profiling on ARM64
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------------------
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Using Linux perf
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~~~~~~~~~~~~~~~~
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The ARM64 architecture provide performance counters to monitor events. The
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Linux ``perf`` tool can be used to profile and benchmark an application. In
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addition to the standard events, ``perf`` can be used to profile arm64
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specific PMU (Performance Monitor Unit) events through raw events (``-e``
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``-rXX``).
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For more derails refer to the
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`ARM64 specific PMU events enumeration <http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.100095_0002_04_en/way1382543438508.html>`_.
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Low-resolution generic counter
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The default ``cntvct_el0`` based ``rte_rdtsc()`` provides a portable means to
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get a wall clock counter in user space. Typically it runs at a lower clock frequency than the CPU clock frequency.
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Cycles counted using this method should be scaled to CPU clock frequency.
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High-resolution cycle counter
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The alternative method to enable ``rte_rdtsc()`` for a high resolution wall
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clock counter is through the ARMv8 PMU subsystem. The PMU cycle counter runs
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at CPU frequency. However, access to the PMU cycle counter from user space is
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not enabled by default in the arm64 linux kernel. It is possible to enable
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cycle counter for user space access by configuring the PMU from the privileged
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mode (kernel space).
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By default the ``rte_rdtsc()`` implementation uses a portable ``cntvct_el0``
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scheme.
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The example below shows the steps to configure the PMU based cycle counter on
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an ARMv8 machine.
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.. code-block:: console
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git clone https://github.com/jerinjacobk/armv8_pmu_cycle_counter_el0
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cd armv8_pmu_cycle_counter_el0
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make
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sudo insmod pmu_el0_cycle_counter.ko
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Please refer to :doc:`../linux_gsg/build_dpdk` for generic details on compiling DPDK with meson.
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In order to enable ``PMU`` based ``rte_rdtsc()``, user needs to configure the
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build with ``-Dc_args='-DRTE_ARM_EAL_RDTSC_USE_PMU'``.
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Example:
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.. code-block:: console
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meson --cross config/arm/arm64_armv8_linux_gcc -Dc_args='-DRTE_ARM_EAL_RDTSC_USE_PMU' build
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.. warning::
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The PMU based scheme is useful for high accuracy performance profiling with
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``rte_rdtsc()``. However, this method can not be used in conjunction with
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Linux userspace profiling tools like ``perf`` as this scheme alters the PMU
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registers state.
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