5630257fcc
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
123 lines
4.4 KiB
ReStructuredText
123 lines
4.4 KiB
ReStructuredText
.. 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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Empty cycles tracing
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~~~~~~~~~~~~~~~~~~~~
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Iterations that yielded no RX packets (empty cycles, wasted iterations) can
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be analyzed using VTune Amplifier. This profiling employs the
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`Instrumentation and Tracing Technology (ITT) API
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<https://software.intel.com/en-us/node/544195>`_
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feature of VTune Amplifier and requires only reconfiguring the DPDK library,
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no changes in a DPDK application are needed.
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To trace wasted iterations on RX queues, first reconfigure DPDK with
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``CONFIG_RTE_ETHDEV_RXTX_CALLBACKS`` and
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``CONFIG_RTE_ETHDEV_PROFILE_ITT_WASTED_RX_ITERATIONS`` enabled.
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Then rebuild DPDK, specifying paths to the ITT header and library, which can
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be found in any VTune Amplifier distribution in the *include* and *lib*
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directories respectively:
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.. code-block:: console
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make EXTRA_CFLAGS=-I<path to ittnotify.h> \
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EXTRA_LDLIBS="-L<path to libittnotify.a> -littnotify"
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Finally, to see wasted iterations in your performance analysis results,
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select the *"Analyze user tasks, events, and counters"* checkbox in the
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*"Analysis Type"* tab when configuring analysis via VTune Amplifier GUI.
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Alternatively, when running VTune Amplifier via command line, specify
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``-knob enable-user-tasks=true`` option.
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Collected regions of wasted iterations will be marked on VTune Amplifier's
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timeline as ITT tasks. These ITT tasks have predefined names, containing
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Ethernet device and RX queue identifiers.
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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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High-resolution cycle 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 <= 100MHz.
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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. Application can choose the PMU based implementation with
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``CONFIG_RTE_ARM_EAL_RDTSC_USE_PMU``.
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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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cd $DPDK_DIR
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make config T=arm64-armv8a-linuxapp-gcc
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echo "CONFIG_RTE_ARM_EAL_RDTSC_USE_PMU=y" >> build/.config
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make
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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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