[dpdk-dev] [PATCH] doc: add how to enable empty cycles profiling

[ilia.kurakin@intel.com]

From: Ilia Kurakin <ilia.kurakin@intel.com>

Programmer's Guide: section "Profile Your Application" updated
with how to enable ITT tasks collection. Based on patch:
http://dpdk.org/dev/patchwork/patch/27158/

Signed-off-by: Ilia Kurakin <ilia.kurakin@intel.com>
---
 doc/guides/prog_guide/profile_app.rst | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/doc/guides/prog_guide/profile_app.rst b/doc/guides/prog_guide/profile_app.rst
index 54b546a..a52fd70 100644
--- a/doc/guides/prog_guide/profile_app.rst
+++ b/doc/guides/prog_guide/profile_app.rst
@@ -59,6 +59,40 @@ Refer to the
 for details about application profiling.
 
 
+Profiling wasted iterations with ITT
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Iterations that yielded no RX packets (wasted loop iterations) can be analyzed
+using Intel® VTune\ :sup:`TM` 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
 ------------------
 
-- 
2.7.4


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