[dpdk-dev] [PATCH v3] doc: arm64: document DPDK application profiling methods

[Jerin Jacob]

Signed-off-by: Jerin Jacob <jerin.jacob at caviumnetworks.com>
Signed-off-by: John McNamara <john.mcnamara at intel.com>
---
v3:
Fixed formatting issues:
- Remove the introduction heading and put intro text under the main heading(Thomas)
- Fixed RST formatting issues such as enclosing technical terms in backquotes(John)
Thanks, John for providing the updated version
v2:
-Addressed ARM64 specific review comments(Suggested by Thomas)
http://dpdk.org/dev/patchwork/patch/16362/
---
 doc/guides/prog_guide/profile_app.rst | 64 ++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/doc/guides/prog_guide/profile_app.rst b/doc/guides/prog_guide/profile_app.rst
index 3226187..54b546a 100644
--- a/doc/guides/prog_guide/profile_app.rst
+++ b/doc/guides/prog_guide/profile_app.rst
@@ -31,8 +31,15 @@
 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.
+Some tools provided by Intel, such as VTune, 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.
@@ -50,3 +57,58 @@ 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.
+
+
+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.
-- 
2.5.5