Profile Your Application
========================
+The following sections describe methods of profiling DPDK applications on
+different architectures.
+
+
+Profiling on x86
+----------------
+
Intel processors provide performance counters to monitor events.
-Some tools provided by Intel can be used to profile and benchmark an application.
-See the *VTune™ Performance Analyzer Essentials* publication from Intel Press for more information.
+Some tools provided by Intel, such as Intel® VTune™ Amplifier, can be used
+to profile and benchmark an application.
+See the *VTune Performance Analyzer Essentials* publication from Intel Press for more information.
-For an Intel® DPDK application, this can be done in a Linux* application environment only.
+For a DPDK application, this can be done in a Linux* application environment only.
The main situations that should be monitored through event counters are:
Refer to the
`Intel Performance Analysis Guide <http://software.intel.com/sites/products/collateral/hpc/vtune/performance_analysis_guide.pdf>`_
for details about application profiling.
+
+
+Empty cycles tracing
+~~~~~~~~~~~~~~~~~~~~
+
+Iterations that yielded no RX packets (empty cycles, wasted iterations) can
+be analyzed using VTune Amplifier. This profiling employs the
+`Instrumentation and Tracing Technology (ITT) API
+<https://software.intel.com/en-us/node/544195>`_
+feature of VTune Amplifier and requires only reconfiguring the DPDK library,
+no changes in a DPDK application are needed.
+
+To trace wasted iterations on RX queues, first reconfigure DPDK with
+``CONFIG_RTE_ETHDEV_RXTX_CALLBACKS`` and
+``CONFIG_RTE_ETHDEV_PROFILE_ITT_WASTED_RX_ITERATIONS`` enabled.
+
+Then rebuild DPDK, specifying paths to the ITT header and library, which can
+be found in any VTune Amplifier distribution in the *include* and *lib*
+directories respectively:
+
+.. code-block:: console
+
+ make EXTRA_CFLAGS=-I<path to ittnotify.h> \
+ EXTRA_LDLIBS="-L<path to libittnotify.a> -littnotify"
+
+Finally, to see wasted iterations in your performance analysis results,
+select the *"Analyze user tasks, events, and counters"* checkbox in the
+*"Analysis Type"* tab when configuring analysis via VTune Amplifier GUI.
+Alternatively, when running VTune Amplifier via command line, specify
+``-knob enable-user-tasks=true`` option.
+
+Collected regions of wasted iterations will be marked on VTune Amplifier's
+timeline as ITT tasks. These ITT tasks have predefined names, containing
+Ethernet device and RX queue identifiers.
+
+
+Profiling on ARM64
+------------------
+
+Using Linux perf
+~~~~~~~~~~~~~~~~
+
+The ARM64 architecture provide performance counters to monitor events. The
+Linux ``perf`` tool can be used to profile and benchmark an application. In
+addition to the standard events, ``perf`` can be used to profile arm64
+specific PMU (Performance Monitor Unit) events through raw events (``-e``
+``-rXX``).
+
+For more derails refer to the
+`ARM64 specific PMU events enumeration <http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.100095_0002_04_en/way1382543438508.html>`_.
+
+
+High-resolution cycle counter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The default ``cntvct_el0`` based ``rte_rdtsc()`` provides a portable means to
+get a wall clock counter in user space. Typically it runs at <= 100MHz.
+
+The alternative method to enable ``rte_rdtsc()`` for a high resolution wall
+clock counter is through the armv8 PMU subsystem. The PMU cycle counter runs
+at CPU frequency. However, access to the PMU cycle counter from user space is
+not enabled by default in the arm64 linux kernel. It is possible to enable
+cycle counter for user space access by configuring the PMU from the privileged
+mode (kernel space).
+
+By default the ``rte_rdtsc()`` implementation uses a portable ``cntvct_el0``
+scheme. Application can choose the PMU based implementation with
+``CONFIG_RTE_ARM_EAL_RDTSC_USE_PMU``.
+
+The example below shows the steps to configure the PMU based cycle counter on
+an armv8 machine.
+
+.. code-block:: console
+
+ git clone https://github.com/jerinjacobk/armv8_pmu_cycle_counter_el0
+ cd armv8_pmu_cycle_counter_el0
+ make
+ sudo insmod pmu_el0_cycle_counter.ko
+ cd $DPDK_DIR
+ make config T=arm64-armv8a-linuxapp-gcc
+ echo "CONFIG_RTE_ARM_EAL_RDTSC_USE_PMU=y" >> build/.config
+ make
+
+.. warning::
+
+ The PMU based scheme is useful for high accuracy performance profiling with
+ ``rte_rdtsc()``. However, this method can not be used in conjunction with
+ Linux userspace profiling tools like ``perf`` as this scheme alters the PMU
+ registers state.
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