+Lab 3: Fixed experiment duration
+--------------------------------
+
+In the current version, the number of tasks is defined through the
+worker arguments. Hence, tasks are created at the very beginning of
+the simulation. Instead, have the master dispatching tasks for a
+predetermined amount of time. The tasks must now be created on demand
+instead of beforehand.
+
+Of course, usual time functions like ``gettimeofday`` will give you the
+time on your real machine, which is prety useless in the
+simulation. Instead, retrieve the time in the simulated world with
+:cpp:func:`simgrid::s4u::Engine::get_clock`.
+
+You can still stop your workers with a specific task as previously,
+or you may kill them forcefully with
+:cpp:func:`simgrid::s4u::Actor::kill` (if you already have a reference
+to the actor you want to kill) or
+:cpp:func:`simgrid::s4u::Actor::kill(aid_t)` (if you only have its ID).
+
+
+Anyway, the new deployment `deployment3.xml` file should thus look
+like this:
+
+.. literalinclude:: tuto_s4u/deployment3.xml
+ :language: xml
+
+Controlling the message verbosity
+.................................
+
+Not all messages are equally informative, so you probably want to
+change most of the ``XBT_INFO`` into ``XBT_DEBUG`` so that they are hidden
+by default. You could for example show only the total number of tasks
+processed by default. You can still see the debug messages as follows:
+
+.. code-block:: shell
+
+ ./masterworker examples/platforms/small_platform.xml deployment3.xml --log=msg_test.thres:debug
+
+
+Lab 4: Understanding competing applications
+-------------------------------------------
+
+It is now time to start several applications at once, with the following ``deployment4.xml`` file.
+
+.. literalinclude:: tuto_s4u/deployment4.xml
+ :language: xml
+
+Things happen when you do so, but it remains utterly difficult to
+understand what's happening exactely. Even Gantt visualizations
+contain too much information to be useful: it is impossible to
+understand which task belong to which application. To fix this, we
+will categorize the tasks.
+
+For that, first let each master create its own category of tasks with
+@ref TRACE_category(), and then assign this category to each task using
+@ref MSG_task_set_category().
+
+The outcome can then be visualized as a Gantt-chart as follows:
+
+.. code-block:: shell
+
+ ./masterworker examples/platforms/small_platform.xml deployment4.xml --cfg=tracing:yes --cfg=tracing/msg/process:yes
+ vite simgrid.trace
+
+.. todo::
+
+ Make it work
+
+Going further
+.............
+
+vite is not enough to understand the situation, because it does not
+deal with categorization. That is why you should switch to R to
+visualize your outcomes, as explained on `this page
+<http://simgrid.gforge.inria.fr/contrib/R_visualization.php>`_.
+
+
