.. SPDX-License-Identifier: BSD-3-Clause Copyright(c) 2010-2014 Intel Corporation. Profile Your Application ======================== The following sections describe methods of profiling DPDK applications on different architectures. Performance counter based profiling ----------------------------------- Modern CPU architectures are equipped with Performance Monitoring Units (PMUs), which provide programmable counters to monitor specific hardware events, such as cache hits, instruction counts, and branch predictions. Tools like Linux perf utilize PMUs to gather performance data. However, in scenarios where CPU cores are isolated, running dedicated tasks and performance of some specific regions of code must be analyzed, extra overhead may be undesirable. In such cases, applications can directly access PMU data using the ``rte_pmu_read()`` function. Access requirements ~~~~~~~~~~~~~~~~~~~ Only Linux is supported. Userspace applications may be restricted, due to various reasons, from accessing PMU internals. To enable access, ``/proc/sys/kernel/perf_event_paranoid`` should be set to ``2`` and application should have ``CAP_PERFMON`` capability assigned. For comprehensive information on security implications and configuration, refer to `Linux documentation `_. Limitations ~~~~~~~~~~~ Current implementation imposes certain limitations: * Only EAL lcores are supported. * EAL lcores must not share a CPU. * Each EAL lcore measures the same group of events. Profiling on x86 ---------------- Intel processors provide performance counters to monitor events. 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 a DPDK application, this can be done in a Linux* application environment only. The main situations that should be monitored through event counters are: * Cache misses * Branch mis-predicts * DTLB misses * Long latency instructions and exceptions Refer to the `Intel Performance Analysis Guide `_ for details about application profiling. Profiling with VTune ~~~~~~~~~~~~~~~~~~~~ To allow VTune attaching to the DPDK application, reconfigure a DPDK build folder by passing ``-Dc_args=-DRTE_ETHDEV_PROFILE_WITH_VTUNE`` meson option and recompile the DPDK: .. code-block:: console meson setup build meson configure build -Dc_args=-DRTE_ETHDEV_PROFILE_WITH_VTUNE ninja -C build 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 details refer to the `ARM64 specific PMU events enumeration `_. Low-resolution generic 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 a lower clock frequency than the CPU clock frequency. Cycles counted using this method should be scaled to CPU clock frequency. High-resolution cycle counter ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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. 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 Please refer to :doc:`../linux_gsg/build_dpdk` for generic details on compiling DPDK with meson. In order to enable ``PMU`` based ``rte_rdtsc()``, user needs to configure the build with ``-Dc_args='-DRTE_ARM_EAL_RDTSC_USE_PMU'``. Example: .. code-block:: console meson setup --cross config/arm/arm64_armv8_linux_gcc -Dc_args='-DRTE_ARM_EAL_RDTSC_USE_PMU' build .. 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.