libperf: Initial documentation

Add initial drafts of documentation files, hugely unfinished.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20190721112506.12306-80-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/lib/Documentation/tutorial/tutorial.rst

@@ -0,0 +1,123 @@
+.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+libperf tutorial
+================
+
+Compile and install libperf from kernel sources
+===============================================
+.. code-block:: bash
+
+  git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
+  cd linux/tools/perf/lib
+  make
+  sudo make install prefix=/usr
+
+Libperf object
+==============
+The libperf library provides several high level objects:
+
+struct perf_cpu_map
+  Provides a cpu list abstraction.
+
+struct perf_thread_map
+  Provides a thread list abstraction.
+
+struct perf_evsel
+  Provides an abstraction for single a perf event.
+
+struct perf_evlist
+  Gathers several struct perf_evsel object and performs functions on all of them.
+
+The exported API binds these objects together,
+for full reference see the libperf.7 man page.
+
+Examples
+========
+Examples aim to explain libperf functionality on simple use cases.
+They are based in on a checked out linux kernel git tree:
+
+.. code-block:: bash
+
+  $ cd tools/perf/lib/Documentation/tutorial/
+  $ ls -d  ex-*
+  ex-1-compile  ex-2-evsel-stat  ex-3-evlist-stat
+
+ex-1-compile example
+====================
+This example shows the basic usage of *struct perf_cpu_map*,
+how to create it and display its cpus:
+
+.. code-block:: bash
+
+  $ cd ex-1-compile/
+  $ make
+  gcc -o test test.c -lperf
+  $ ./test
+  0 1 2 3 4 5 6 7
+
+
+The full code listing is here:
+
+.. code-block:: c
+
+   1 #include <perf/cpumap.h>
+   2
+   3 int main(int argc, char **Argv)
+   4 {
+   5         struct perf_cpu_map *cpus;
+   6         int cpu, tmp;
+   7
+   8         cpus = perf_cpu_map__new(NULL);
+   9
+  10         perf_cpu_map__for_each_cpu(cpu, tmp, cpus)
+  11                 fprintf(stdout, "%d ", cpu);
+  12
+  13         fprintf(stdout, "\n");
+  14
+  15         perf_cpu_map__put(cpus);
+  16         return 0;
+  17 }
+
+
+First you need to include the proper header to have *struct perf_cpumap*
+declaration and functions:
+
+.. code-block:: c
+
+   1 #include <perf/cpumap.h>
+
+
+The *struct perf_cpumap* object is created by *perf_cpu_map__new* call.
+The *NULL* argument asks it to populate the object with the current online CPUs list:
+
+.. code-block:: c
+
+   8         cpus = perf_cpu_map__new(NULL);
+
+This is paired with a *perf_cpu_map__put*, that drops its reference at the end, possibly deleting it.
+
+.. code-block:: c
+
+  15         perf_cpu_map__put(cpus);
+
+The iteration through the *struct perf_cpumap* CPUs is done using the *perf_cpu_map__for_each_cpu*
+macro which requires 3 arguments:
+
+- cpu  - the cpu numer
+- tmp  - iteration helper variable
+- cpus - the *struct perf_cpumap* object
+
+.. code-block:: c
+
+  10         perf_cpu_map__for_each_cpu(cpu, tmp, cpus)
+  11                 fprintf(stdout, "%d ", cpu);
+
+ex-2-evsel-stat example
+=======================
+
+TBD
+
+ex-3-evlist-stat example
+========================
+
+TBD