X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/ce930ad96b622e2b3856b7d9c3d97e60ec2c93a1..07ac6b8627cd7a368453d55197ecc421f9cb6eae:/docs/source/Configuring_SimGrid.rst

diff --git a/docs/source/Configuring_SimGrid.rst b/docs/source/Configuring_SimGrid.rst
index c629d166ac..a715cc9208 100644
--- a/docs/source/Configuring_SimGrid.rst
+++ b/docs/source/Configuring_SimGrid.rst
@@ -5,7 +5,7 @@ Configuring SimGrid
 
 .. raw:: html
 
-   <object id="TOC" data="graphical-toc.svg" width="100%" type="image/svg+xml"></object>
+   <object id="TOC" data="graphical-toc.svg" type="image/svg+xml"></object>
    <script>
    window.onload=function() { // Wait for the SVG to be loaded before changing it
      var elem=document.querySelector("#TOC").contentDocument.getElementById("ConfigBox")
@@ -32,9 +32,9 @@ The most common way is to use the ``--cfg`` command line argument. For
 example, to set the item ``Item`` to the value ``Value``, simply
 type the following on the command-line:
 
-.. code-block:: shell
+.. code-block:: console
 
-   my_simulator --cfg=Item:Value (other arguments)
+   $ my_simulator --cfg=Item:Value (other arguments)
 
 Several ``--cfg`` command line arguments can naturally be used. If you
 need to include spaces in the argument, don't forget to quote the
@@ -67,7 +67,7 @@ with :cpp:func:`simgrid::s4u::Engine::set_config` or :cpp:func:`MSG_config`.
    int main(int argc, char *argv[]) {
      simgrid::s4u::Engine e(&argc, argv);
 
-     e->set_config("Item:Value");
+     simgrid::s4u::Engine::set_config("Item:Value");
 
      // Rest of your code
    }
@@ -84,10 +84,12 @@ Existing Configuration Items
   option. For example, ``--cfg=plugin:help`` will give you the list
   of plugins available in your installation of SimGrid.
 
+- **bmf/max-iterations:** :ref:`cfg=bmf/max-iterations`
+- **bmf/precision:** :ref:`cfg=bmf/precision`
+
 - **contexts/factory:** :ref:`cfg=contexts/factory`
 - **contexts/guard-size:** :ref:`cfg=contexts/guard-size`
 - **contexts/nthreads:** :ref:`cfg=contexts/nthreads`
-- **contexts/parallel-threshold:** :ref:`cfg=contexts/parallel-threshold`
 - **contexts/stack-size:** :ref:`cfg=contexts/stack-size`
 - **contexts/synchro:** :ref:`cfg=contexts/synchro`
 
@@ -117,6 +119,7 @@ Existing Configuration Items
 - **model-check/reduction:** :ref:`cfg=model-check/reduction`
 - **model-check/replay:** :ref:`cfg=model-check/replay`
 - **model-check/send-determinism:** :ref:`cfg=model-check/send-determinism`
+- **model-check/setenv:** :ref:`cfg=model-check/setenv`
 - **model-check/termination:** :ref:`cfg=model-check/termination`
 - **model-check/timeout:** :ref:`cfg=model-check/timeout`
 - **model-check/visited:** :ref:`cfg=model-check/visited`
@@ -124,6 +127,8 @@ Existing Configuration Items
 - **network/bandwidth-factor:** :ref:`cfg=network/bandwidth-factor`
 - **network/crosstraffic:** :ref:`cfg=network/crosstraffic`
 - **network/latency-factor:** :ref:`cfg=network/latency-factor`
+- **network/loopback-lat:** :ref:`cfg=network/loopback`
+- **network/loopback-bw:** :ref:`cfg=network/loopback`
 - **network/maxmin-selective-update:** :ref:`Network Optimization Level <options_model_optim>`
 - **network/model:** :ref:`options_model_select`
 - **network/optim:** :ref:`Network Optimization Level <options_model_optim>`
@@ -131,6 +136,7 @@ Existing Configuration Items
 - **network/weight-S:** :ref:`cfg=network/weight-S`
 
 - **ns3/TcpModel:** :ref:`options_pls`
+- **ns3/seed:** :ref:`options_pls`
 - **path:** :ref:`cfg=path`
 - **plugin:** :ref:`cfg=plugin`
 
@@ -139,13 +145,17 @@ Existing Configuration Items
 - **surf/precision:** :ref:`cfg=surf/precision`
 
 - **For collective operations of SMPI,** please refer to Section :ref:`cfg=smpi/coll-selector`
+- **smpi/auto-shared-malloc-thresh:** :ref:`cfg=smpi/auto-shared-malloc-thresh`
 - **smpi/async-small-thresh:** :ref:`cfg=smpi/async-small-thresh`
+- **smpi/barrier-finalization:** :ref:`cfg=smpi/barrier-finalization`
+- **smpi/barrier-collectives:** :ref:`cfg=smpi/barrier-collectives`
 - **smpi/buffering:** :ref:`cfg=smpi/buffering`
-- **smpi/bw-factor:** :ref:`cfg=smpi/bw-factor`
 - **smpi/coll-selector:** :ref:`cfg=smpi/coll-selector`
 - **smpi/comp-adjustment-file:** :ref:`cfg=smpi/comp-adjustment-file`
 - **smpi/cpu-threshold:** :ref:`cfg=smpi/cpu-threshold`
+- **smpi/display-allocs:** :ref:`cfg=smpi/display-allocs`
 - **smpi/display-timing:** :ref:`cfg=smpi/display-timing`
+- **smpi/errors-are-fatal:** :ref:`cfg=smpi/errors-are-fatal`
 - **smpi/grow-injected-times:** :ref:`cfg=smpi/grow-injected-times`
 - **smpi/host-speed:** :ref:`cfg=smpi/host-speed`
 - **smpi/IB-penalty-factors:** :ref:`cfg=smpi/IB-penalty-factors`
@@ -153,11 +163,11 @@ Existing Configuration Items
 - **smpi/iprobe-cpu-usage:** :ref:`cfg=smpi/iprobe-cpu-usage`
 - **smpi/init:** :ref:`cfg=smpi/init`
 - **smpi/keep-temps:** :ref:`cfg=smpi/keep-temps`
-- **smpi/lat-factor:** :ref:`cfg=smpi/lat-factor`
 - **smpi/ois:** :ref:`cfg=smpi/ois`
 - **smpi/or:** :ref:`cfg=smpi/or`
 - **smpi/os:** :ref:`cfg=smpi/os`
 - **smpi/papi-events:** :ref:`cfg=smpi/papi-events`
+- **smpi/pedantic:** :ref:`cfg=smpi/pedantic`
 - **smpi/privatization:** :ref:`cfg=smpi/privatization`
 - **smpi/privatize-libs:** :ref:`cfg=smpi/privatize-libs`
 - **smpi/send-is-detached-thresh:** :ref:`cfg=smpi/send-is-detached-thresh`
@@ -166,6 +176,7 @@ Existing Configuration Items
 - **smpi/simulate-computation:** :ref:`cfg=smpi/simulate-computation`
 - **smpi/test:** :ref:`cfg=smpi/test`
 - **smpi/wtime:** :ref:`cfg=smpi/wtime`
+- **smpi/list-leaks** :ref:`cfg=smpi/list-leaks`
 
 - **Tracing configuration options** can be found in Section :ref:`tracing_tracing_options`
 
@@ -225,7 +236,7 @@ models for all existing resources.
 - ``cpu/model``: specify the used CPU model.  We have only one model
   for now:
 
-  - **Cas01:** Simplistic CPU model (time=size/power)
+  - **Cas01:** Simplistic CPU model (time=size/speed)
 
 - ``host/model``: The host concept is the aggregation of a CPU with a
   network card. Three models exists, but actually, only 2 of them are
@@ -234,8 +245,7 @@ models for all existing resources.
   end, you have two host models: The default one allows aggregation of
   an existing CPU model with an existing network model, but does not
   allow parallel tasks because these beasts need some collaboration
-  between the network and CPU model. That is why, ptask_07 is used by
-  default when using SimDag.
+  between the network and CPU model.
 
   - **default:** Default host model. Currently, CPU:Cas01 and
     network:LV08 (with cross traffic enabled)
@@ -252,12 +262,32 @@ models for all existing resources.
 
 .. todo: make 'compound' the default host model.
 
+.. _options_model_solver:
+
+Solver
+......
+
+The different models rely on a linear inequalities solver to share
+the underlying resources. SimGrid allows you to change the solver, but
+be cautious, **don't change it unless you are 100% sure**.
+ 
+  - items ``cpu/solver``, ``network/solver``, ``disk/solver`` and  ``host/solver``
+    allow you to change the solver for each model:
+
+    - **maxmin:** The default solver for all models except ptask. Provides a
+      max-min fairness allocation.
+    - **fairbottleneck:** The default solver for ptasks. Extends max-min to
+      allow heterogeneous resources.
+    - **bmf:** More realistic solver for heterogeneous resource sharing.
+      Implements BMF (Bottleneck max fairness) fairness. To be used with
+      parallel tasks instead of fair-bottleneck.
+
 .. _options_model_optim:
 
 Optimization Level
 ..................
 
-The network and CPU models that are based on lmm_solve (that
+The network and CPU models that are based on linear inequalities solver (that
 is, all our analytical models) accept specific optimization
 configurations.
 
@@ -284,14 +314,16 @@ configurations.
     the dependency induced by the backbone), but through a complicated
     and slow pattern that follows the actual dependencies.
 
+.. _cfg=bmf/precision:
 .. _cfg=maxmin/precision:
 .. _cfg=surf/precision:
 
 Numerical Precision
 ...................
 
-**Option** ``maxmin/precision`` **Default:** 0.00001 (in flops or bytes) |br|
-**Option** ``surf/precision`` **Default:** 0.00001 (in seconds)
+**Option** ``maxmin/precision`` **Default:** 1e-5 (in flops or bytes) |br|
+**Option** ``surf/precision`` **Default:** 1e-9 (in seconds) |br|
+**Option** ``bmf/precision`` **Default:** 1e-12 (no unit)
 
 The analytical models handle a lot of floating point values. It is
 possible to change the epsilon used to update and compare them through
@@ -320,6 +352,17 @@ Such limitations help both to the simulation speed and simulation accuracy
 on highly constrained scenarios, but the simulation speed suffers of this
 setting on regular (less constrained) scenarios so it is off by default.
 
+.. _cfg=bmf/max-iterations:
+
+BMF settings
+............
+
+**Option** ``bmf/max-iterations`` **Default:** 1000
+
+It may happen in some settings that the BMF solver fails to converge to
+a solution, so there is a hard limit on the amount of iteration count to
+avoid infinite loops.
+
 .. _options_model_network:
 
 Configuring the Network Model
@@ -337,42 +380,134 @@ the TCP congestion mechanism into account.  On Linux, this value can
 be retrieved using the following commands. Both give a set of values,
 and you should use the last one, which is the maximal size.
 
-.. code-block:: shell
+.. code-block:: console
 
-   cat /proc/sys/net/ipv4/tcp_rmem # gives the sender window
-   cat /proc/sys/net/ipv4/tcp_wmem # gives the receiver window
+   $ cat /proc/sys/net/ipv4/tcp_rmem # gives the sender window
+   $ cat /proc/sys/net/ipv4/tcp_wmem # gives the receiver window
 
-.. _cfg=smpi/IB-penalty-factors:
 .. _cfg=network/bandwidth-factor:
 .. _cfg=network/latency-factor:
 .. _cfg=network/weight-S:
 
-Correcting Important Network Parameters
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Manual calibration factors
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+SimGrid can take network irregularities such as a slow startup or changing behavior depending on the message size into account.
+The values provided by default were computed a long time ago through data fitting one the timings of either packet-level simulators or direct
+experiments on real platforms. These default values should be OK for most users, but if simulation realism is really important to
+you, you probably want to recalibrate the models (i.e., devise sensible values for your specific settings). This section only
+describes how to pass new values to the models while the calibration process involved in the computation of these values is
+described :ref:`in the relevant chapter <models_calibration>`.
+
+We found out that many networking effects can be realistically accounted for with the three following correction factors. They were shown
+to be enough to capture slow-start effects, the different transmission modes of MPI systems (eager vs. rendez-vous mode), or the
+non linear effects of wifi sharing.
+
+**Option** ``network/latency-factor`` **Default:** 1.0, but overridden by most models
+
+This option specifies a multiplier to apply to the *physical* latency (i.e., the one described in the platform) of the set of links involved in a communication. The factor can either be a constant to apply to any
+communication, or it may depend on the message size. The ``CM02`` model does not use any correction factor, so the
+latency-factor remains to 1. The ``LV08`` model sets it to 13.01 to model slow-start, while the ``SMPI`` model has several
+possible values depending on the interval in which the message size falls. The default SMPI setting given below specifies for example that a message smaller than
+257 bytes will get a latency multiplier of 2.01467 while a message whose size is in [15424, 65472] will get a latency multiplier
+of 3.48845. The ``wifi`` model goes further and uses a callback in the program to compute the factor that must be non-linear in
+this case.
+
+This multiplier is applied to the latency computed from the platform, that is the sum of all link *physical* latencies over the :ref:`network path <platform_routing>` used by the considered communication, to derive the *effective* end-to-end latency.
+
+Constant factors are easy to express, but the interval-based syntax used in SMPI is somewhat complex. It expects a set of
+factors separated by semicolons, each of the form ``boundary:factor``. For example if your specification is
+``0:1;1000:2;5000:3``, it means that on [0, 1000) the factor is 1. On [1000,5000), the factor is 2 while the factor is 3 for
+5000 and beyond. If your first interval does include size=0, then the default value of 1 is used before. Changing the factor
+callback is not possible from the command line and must be done from your code, as shown in `this example
+<https://framagit.org/simgrid/simgrid/tree/master/examples/cpp/network-factors/s4u-network-factors.cpp>`_. Note that the chosen
+model only provide some default settings, not more. You can pick a ``LV08`` to get some of the settings, and override the latency
+with an interval-based value.
+
+SMPI default value: 65472:11.6436; 15424:3.48845; 9376:2.59299; 5776:2.18796; 3484:1.88101; 1426:1.61075; 732:1.9503;
+257:1.95341;0:2.01467 (interval boundaries are sorted automatically). These values were computed by data fitting on the Stampede
+Supercomputer at TACC, with optimal deployment of processes on nodes. To accurately model your settings, you should redo the
+:ref:`calibration <models_calibration>`.
 
-SimGrid can take network irregularities such as a slow startup or
-changing behavior depending on the message size into account.  You
-should not change these values unless you really know what you're
-doing.  The corresponding values were computed through data fitting
-one the timings of packet-level simulators, as described in `Accuracy
-Study and Improvement of Network Simulation in the SimGrid Framework
-<http://mescal.imag.fr/membres/arnaud.legrand/articles/simutools09.pdf>`_.
+**Option** ``network/bandwidth-factor`` **Default:** 1.0, but overridden by most models
 
+Setting this option automatically adjusts the *effective* bandwidth (i.e., the one perceived by the application) used by any given communication. As with latency-factor above, the value
+can be a constant (``CM02`` uses 1 -- no correction -- while ``LV08`` uses 0.97 to discount TCP headers while computing the
+payload bandwidth), interval-based (as the default provided by the ``SMPI``), or using in-program callbacks (as with ``wifi``).
 
-If you are using the SMPI model, these correction coefficients are
-themselves corrected by constant values depending on the size of the
-exchange.  By default SMPI uses factors computed on the Stampede
-Supercomputer at TACC, with optimal deployment of processes on
-nodes. Again, only hardcore experts should bother about this fact.
+SMPI default value: 65472:0.940694;15424:0.697866;9376:0.58729;5776:1.08739;3484:0.77493;1426:0.608902;732:0.341987;257:0.338112;0:0.812084 
+This was also computed on the Stampede Supercomputer.
+
+**Option** ``network/weight-S`` **Default:** depends on the model
+
+Value used to account for RTT-unfairness when sharing a bottleneck (network connections with a large RTT are generally penalized against those with a small one). Described in `Accuracy Study and Improvement of Network
+Simulation in the SimGrid Framework <http://mescal.imag.fr/membres/arnaud.legrand/articles/simutools09.pdf>`_
+
+Default values for ``CM02`` is 0. ``LV08`` sets it to 20537 while both ``SMPI`` and ``IB`` set it to 8775.
+
+.. _cfg=network/loopback:
+
+Configuring loopback link
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Several network models provide an implicit loopback link to account for local
+communication on a host. By default it has a 10GBps bandwidth and a null latency.
+This can be changed with ``network/loopback-lat`` and ``network/loopback-bw``
+items. Note that this loopback is conveniently modeled with a :ref:`single FATPIPE link  <pf_loopback>`
+for the whole platform. If modeling contention inside nodes is important then you should
+rather add such loopback links (one for each host) yourself.
+
+.. _cfg=smpi/IB-penalty-factors:
+
+Infiniband model
+^^^^^^^^^^^^^^^^
 
 InfiniBand network behavior can be modeled through 3 parameters
-``smpi/IB-penalty-factors:"βe;βs;γs"``, as explained in `this PhD
-thesis
-<http://mescal.imag.fr/membres/jean-marc.vincent/index.html/PhD/Vienne.pdf>`_.
+``smpi/IB-penalty-factors:"βe;βs;γs"``, as explained in `the PhD
+thesis of Jean-Marc Vincent
+<http://mescal.imag.fr/membres/jean-marc.vincent/index.html/PhD/Vienne.pdf>`_ (in French)
+or more concisely in `this paper <https://hal.inria.fr/hal-00953618/document>`_,
+even if that paper does only describe models for myrinet and ethernet.
+You can see in Fig 2 some results for Infiniband, for example. This model
+may be outdated by now for modern infiniband, anyway, so a new
+validation would be good.
+
+The three paramaters are defined as follows:
+
+- βs: penalty factor for outgoing messages, computed by running a simple send to
+  two nodes and checking slowdown compared to a single send to one node,
+  dividing by 2
+- βe: penalty factor for ingoing messages, same computation method but with one
+  node receiving several messages
+- γr: slowdown factor when communication buffer memory is saturated. It needs a
+  more complicated pattern to run in order to be computed (5.3 in the thesis,
+  page 107), and formula in the end is γr = time(c)/(3×βe×time(ref)), where
+  time(ref) is the time of a single comm with no contention).
+
+Once these values are computed, a penalty is assessed for each message (this is
+the part implemented in the simulator) as shown page 106 of the thesis. Here is
+a simple translation of this text. First, some notations:
+
+- ∆e(e) which corresponds to the incoming degree of node e, that is to say the number of communications having as destination node e.
+- ∆s (s) which corresponds to the degree outgoing from node s, that is to say the number of communications sent by node s.
+- Φ (e) which corresponds to the number of communications destined for the node e but coming from a different node.
+- Ω (s, e) which corresponds to the number of messages coming from node s to node e. If node e only receives communications from different nodes then Φ (e) = ∆e (e). On the other hand if, for example, there are three messages coming from node s and going from node e then Φ (e) 6 = ∆e (e) and Ω (s, e) = 3
+
+To determine the penalty for a communication, two values need to be calculated. First, the penalty caused by the conflict in transmission, noted ps.
+
+
+- if ∆s (i) = 1 then ps = 1.
+- if ∆s (i) ≥ 2 and ∆e (i) ≥ 3 then ps = ∆s (i) × βs × γr
+- else, ps = ∆s (i) × βs
 
-.. todo:: This section should be rewritten, and actually explain the
-	  options network/bandwidth-factor, network/latency-factor,
-	  network/weight-S.
+
+Then,  the penalty caused by the conflict in reception (noted pe) should be computed as follows:
+
+- if ∆e (i) = 1 then pe = 1
+- else, pe = Φ (e) × βe × Ω (s, e)
+
+Finally, the penalty associated with the communication is:
+p = max (ps ∈ s, pe)
 
 .. _cfg=network/crosstraffic:
 
@@ -402,9 +537,9 @@ Simulating Asynchronous Send
 
 (this configuration item is experimental and may change or disappear)
 
-It is possible to specify that messages below a certain size will be
+It is possible to specify that messages below a certain size (in bytes) will be
 sent as soon as the call to MPI_Send is issued, without waiting for
-the correspondant receive. This threshold can be configured through
+the correspondent receive. This threshold can be configured through
 the ``smpi/async-small-thresh`` item. The default value is 0. This
 behavior can also be manually set for mailboxes, by setting the
 receiving mode of the mailbox with a call to
@@ -428,12 +563,21 @@ ns-3. The only valid values (enforced on the SimGrid side) are
 'default' (no change to the ns-3 configuration), 'NewReno' or 'Reno' or
 'Tahoe'.
 
+**Option** ``ns3/seed`` **Default:** "" (don't set the seed in ns-3)
+
+This option is the random seed to provide to ns-3 with
+``ns3::RngSeedManager::SetSeed`` and ``ns3::RngSeedManager::SetRun``.
+
+If left blank, no seed is set in ns-3. If the value 'time' is
+provided, the current amount of seconds since epoch is used as a seed.
+Otherwise, the provided value must be a number to use as a seed.
+
 Configuring the Storage model
 .............................
 
 .. _cfg=storage/max_file_descriptors:
 
-File Descriptor Cound per Host
+File Descriptor Count per Host
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 **Option** ``storage/max_file_descriptors`` **Default:** 1024
@@ -476,9 +620,9 @@ Configuring the Model-Checking
 To enable SimGrid's model-checking support, the program should
 be executed using the simgrid-mc wrapper:
 
-.. code-block:: shell
+.. code-block:: console
 
-   simgrid-mc ./my_program
+   $ simgrid-mc ./my_program
 
 Safety properties are expressed as assertions using the function
 :cpp:func:`void MC_assert(int prop)`.
@@ -504,10 +648,10 @@ In SMPI, this depends on the message size, that is compared against two threshol
 - if (:ref:`smpi/send-is-detached-thresh <cfg=smpi/send-is-detached-thresh>` < size) then
   MPI_Send returns only when the message has actually been sent over the network. This is known as the rendez-vous mode.
 
-The ``smpi/buffering`` option gives an easier interface to choose between these semantics. It can take two values:
+The ``smpi/buffering`` (only valid with MC) option gives an easier interface to choose between these semantics. It can take two values:
 
-- **zero:** means that buffering should be disabled. Blocking communications are actually blocking.
-- **infty:** means that buffering should be made infinite. Blocking communications are non-blocking.
+- **zero:** means that buffering should be disabled. All communications are actually blocking.
+- **infty:** means that buffering should be made infinite. All communications are non-blocking.
 
 .. _cfg=model-check/property:
 
@@ -519,11 +663,11 @@ Specifying a liveness property
 If you want to specify liveness properties, you have to pass them on
 the command line, specifying the name of the file containing the
 property, as formatted by the `ltl2ba <https://github.com/utwente-fmt/ltl2ba>`_ program.
-Note that ltl2ba is not part of SimGrid and must be installed separatly.
+Note that ltl2ba is not part of SimGrid and must be installed separately.
 
-.. code-block:: shell
+.. code-block:: console
 
-   simgrid-mc ./my_program --cfg=model-check/property:<filename>
+   $ simgrid-mc ./my_program --cfg=model-check/property:<filename>
 
 .. _cfg=model-check/checkpoint:
 
@@ -615,18 +759,18 @@ If set, the ``model-check/dot-output`` configuration item is the name
 of a file in which to write a dot file of the path leading to the
 property violation discovered (safety or liveness violation), as well
 as the cycle for liveness properties. This dot file can then be fed to the
-graphviz dot tool to generate an corresponding graphical representation.
+graphviz dot tool to generate a corresponding graphical representation.
 
 .. _cfg=model-check/max-depth:
 
 Exploration Depth Limit
 .......................
 
-The ``model-checker/max-depth`` can set the maximum depth of the
+The ``model-check/max-depth`` can set the maximum depth of the
 exploration graph of the model checker. If this limit is reached, a
 logging message is sent and the results might not be exact.
 
-By default, there is no depth limit.
+By default, the exploration is limited to the depth of 1000.
 
 .. _cfg=model-check/timeout:
 
@@ -648,6 +792,15 @@ The ``model-check/communications-determinism`` and
 communication determinism mode of the model checker, which checks
 determinism properties of the communications of an application.
 
+.. _cfg=model-check/setenv:
+
+Passing environment variables
+.............................
+
+You can specify extra environment variables to be set in the verified application
+with ``model-check/setenv``. For example, you can preload a library as follows:
+``-cfg=model-check/setenv:LD_PRELOAD=toto;LD_LIBRARY_PATH=/tmp``.
+
 .. _options_mc_perf:
 
 Verification Performance Considerations
@@ -683,7 +836,7 @@ When the model checker finds an interesting path in the application
 execution graph (where a safety or liveness property is violated), it
 generates an identifier for this path. Here is an example of the output:
 
-.. code-block:: shell
+.. code-block:: console
 
    [  0.000000] (0:@) Check a safety property
    [  0.000000] (0:@) **************************
@@ -708,10 +861,11 @@ MC-related options, keep non-MC-related ones and add
 Currently, if the path is of the form ``X;Y;Z``, each number denotes
 the actor's pid that is selected at each indecision point. If it's of
 the form ``X/a;Y/b``, the X and Y are the selected pids while the a
-and b are the return values of their simcalls. In the previouse
+and b are the return values of their simcalls. In the previous
 example, ``1/3;1/4``, you can see from the full output that the actor
 1 is doing MC_RANDOM simcalls, so the 3 and 4 simply denote the values
-that these simcall return.
+that these simcall return on the execution branch leading to the
+violation.
 
 Configuring the User Code Virtualization
 ----------------------------------------
@@ -782,10 +936,16 @@ stacks), leading to segfaults with corrupted stack traces.
 If you want to push the scalability limits of your code, you might
 want to reduce the ``contexts/stack-size`` item. Its default value is
 8192 (in KiB), while our Chord simulation works with stacks as small
-as 16 KiB, for example. This *setting is ignored* when using the
-thread factory. Instead, you should compile SimGrid and your
-application with ``-fsplit-stack``. Note that this compilation flag is
-not compatible with the model checker right now.
+as 16 KiB, for example. You can ensure that some actors have a specific
+size by simply changing the value of this configuration item before
+creating these actors. The :cpp:func:`simgrid::s4u::Engine::set_config`
+functions are handy for that.
+
+This *setting is ignored* when using the thread factory (because there
+is no way to modify the stack size with C++ system threads). Instead,
+you should compile SimGrid and your application with
+``-fsplit-stack``. Note that this compilation flag is not compatible
+with the model checker right now.
 
 The operating system should only allocate memory for the pages of the
 stack which are actually used and you might not need to use this in
@@ -814,7 +974,6 @@ on other parts of the memory if their size is too small for the
 application.
 
 .. _cfg=contexts/nthreads:
-.. _cfg=contexts/parallel-threshold:
 .. _cfg=contexts/synchro:
 
 Running User Code in Parallel
@@ -832,17 +991,6 @@ run. To activate this, set the ``contexts/nthreads`` item to the amount
 of cores that you have in your computer (or lower than 1 to have the
 amount of cores auto-detected).
 
-Even if you asked several worker threads using the previous option,
-you can request to start the parallel execution (and pay the
-associated synchronization costs) only if the potential parallelism is
-large enough. For that, set the ``contexts/parallel-threshold``
-item to the minimal amount of user contexts needed to start the
-parallel execution. In any given simulation round, if that amount is
-not reached, the contexts will be run sequentially directly by the
-main thread (thus saving the synchronization costs). Note that this
-option is mainly useful when the grain of the user code is very fine,
-because our synchronization is now very efficient.
-
 When parallel execution is activated, you can choose the
 synchronization schema used with the ``contexts/synchro`` item,
 which value is either:
@@ -861,45 +1009,42 @@ which value is either:
 Configuring the Tracing
 -----------------------
 
-The :ref:`tracing subsystem <outcomes_vizu>` can be configured in
-several different ways depending on the nature of the simulator (MSG,
-SimDag, SMPI) and the kind of traces that need to be obtained. See the
+The :ref:`tracing subsystem <outcome_vizu>` can be configured in
+several different ways depending on the used interface (S4U, SMPI)
+and the kind of traces that needs to be obtained. See the
 :ref:`Tracing Configuration Options subsection
-<tracing_tracing_options>` to get a detailed description of each
+<tracing_tracing_options>` for a full description of each
 configuration option.
 
 We detail here a simple way to get the traces working for you, even if
 you never used the tracing API.
 
 
-- Any SimGrid-based simulator (MSG, SimDag, SMPI, ...) and raw traces:
+- Any SimGrid-based simulator (MSG, SMPI, ...) and raw traces:
 
-  .. code-block:: shell
+  .. code-block:: none
 
-     --cfg=tracing:yes --cfg=tracing/uncategorized:yes --cfg=triva/uncategorized:uncat.plist
+     --cfg=tracing:yes --cfg=tracing/uncategorized:yes
 
-  The first parameter activates the tracing subsystem, the second
+  The first parameter activates the tracing subsystem, and the second
   tells it to trace host and link utilization (without any
-  categorization) and the third creates a graph configuration file to
-  configure Triva when analysing the resulting trace file.
+  categorization).
 
-- MSG or SimDag-based simulator and categorized traces (you need to
-  declare categories and classify your tasks according to them) 
+- MSG-based simulator and categorized traces (you need to
+  declare categories and classify your tasks according to them)
 
-  .. code-block:: shell
+  .. code-block:: none
 
-     --cfg=tracing:yes --cfg=tracing/categorized:yes --cfg=triva/categorized:cat.plist
+     --cfg=tracing:yes --cfg=tracing/categorized:yes
 
-  The first parameter activates the tracing subsystem, the second
-  tells it to trace host and link categorized utilization and the
-  third creates a graph configuration file to configure Triva when
-  analysing the resulting trace file.
+  The first parameter activates the tracing subsystem, and the second
+  tells it to trace host and link categorized utilization.
 
 - SMPI simulator and traces for a space/time view:
 
-  .. code-block:: shell
+  .. code-block:: console
 
-     smpirun -trace ...
+     $ smpirun -trace ...
 
   The `-trace` parameter for the smpirun script runs the simulation
   with ``--cfg=tracing:yes --cfg=tracing/smpi:yes``. Check the
@@ -911,13 +1056,13 @@ reproduce an experiment. You have two ways to do that:
 
 - Add a string on top of the trace file as comment:
 
-  .. code-block:: shell
+  .. code-block:: none
 
      --cfg=tracing/comment:my_simulation_identifier
 
 - Add the contents of a textual file on top of the trace file as comment:
 
-  .. code-block:: shell
+  .. code-block:: none
 
      --cfg=tracing/comment-file:my_file_with_additional_information.txt
 
@@ -943,9 +1088,8 @@ doing. This option shows a backtrace of the other process.
 Configuring SMPI
 ----------------
 
-The SMPI interface provides several specific configuration items.
-These are not easy to see, since the code is usually launched through the
-``smiprun`` script directly.
+The SMPI interface provides several specific configuration items. 
+These are not easy to see with ``--help-cfg``, since SMPI binaries are usually launched through the ``smiprun`` script.
 
 .. _cfg=smpi/host-speed:
 .. _cfg=smpi/cpu-threshold:
@@ -961,10 +1105,16 @@ a ``MPI_Send()``, SMPI will automatically benchmark the duration of
 this code, and create an execution task within the simulator to take
 this into account. For that, the actual duration is measured on the
 host machine and then scaled to the power of the corresponding
-simulated machine. The variable ``smpi/host-speed`` allows one to specify
-the computational speed of the host machine (in flop/s) to use when
-scaling the execution times. It defaults to 20000, but you really want
-to adjust it to get accurate simulation results.
+simulated machine. The variable ``smpi/host-speed`` allows one to
+specify the computational speed of the host machine (in flop/s by
+default) to use when scaling the execution times.
+
+The default value is ``smpi/host-speed=20kf`` (= 20,000 flop/s). This
+is probably underestimated for most machines, leading SimGrid to
+overestimate the amount of flops in the execution blocks that are
+automatically injected in the simulator. As a result, the execution
+time of the whole application will probably be overestimated until you
+use a realistic value.
 
 When the code consists of numerous consecutive MPI calls, the
 previous mechanism feeds the simulation kernel with numerous tiny
@@ -1018,7 +1168,7 @@ This option allows you to pass a file that contains two columns: The
 first column defines the section that will be subject to a speedup;
 the second column is the speedup. For instance:
 
-.. code-block:: shell
+.. code-block:: none
 
   "start:stop","ratio"
   "exchange_1.f:30:exchange_1.f:130",1.18244559422142
@@ -1038,26 +1188,12 @@ Please note that you must pass the ``-trace-call-location`` flag to
 smpicc or smpiff, respectively. This flag activates some internal
 macro definitions that help with obtaining the call location.
 
-.. _cfg=smpi/bw-factor:
-
-Bandwidth Factors
-.................
-
-**Option** ``smpi/bw-factor``
-|br| **Default:** 65472:0.940694;15424:0.697866;9376:0.58729;5776:1.08739;3484:0.77493;1426:0.608902;732:0.341987;257:0.338112;0:0.812084
-
-The possible throughput of network links is often dependent on the
-message sizes, as protocols may adapt to different message sizes. With
-this option, a series of message sizes and factors are given, helping
-the simulation to be more realistic. For instance, the current default
-value means that messages with size 65472 and more will get a total of
-MAX_BANDWIDTH*0.940694, messages of size 15424 to 65471 will get
-MAX_BANDWIDTH*0.697866, and so on (where MAX_BANDWIDTH denotes the
-bandwidth of the link).
+Bandwidth and latency factors
+.............................
 
-An experimental script to compute these factors is available online. See
-https://framagit.org/simgrid/platform-calibration/
-https://simgrid.org/contrib/smpi-saturation-doc.html
+Adapting the bandwidth and latency acurately to the network conditions is of a paramount importance to get realistic results.
+This is done through the :ref:`network/bandwidth-factor <cfg=network/bandwidth-factor>` and :ref:`network/latency-factor
+<cfg=network/latency-factor>` items. You probably also want to read the following section: :ref:`models_calibration`.
 
 .. _cfg=smpi/display-timing:
 
@@ -1073,6 +1209,23 @@ code, making it difficult to report the simulated time when the
 simulation ends. If you enable the ``smpi/display-timing`` item,
 ``smpirun`` will display this information when the simulation
 ends.
+SMPI will also display information about the amout of real time spent
+in application code and in SMPI internals, to provide hints about the
+need to use sampling to reduce simulation time.
+
+.. _cfg=smpi/display-allocs:
+
+Reporting memory allocations
+............................
+
+**Option** ``smpi/display-allocs`` **Default:** 0 (false)
+
+SMPI intercepts malloc and calloc calls performed inside the running
+application, if it wasn't compiled with SMPI_NO_OVERRIDE_MALLOC.
+With this option, SMPI will show at the end of execution the amount of
+memory allocated through these calls, and locate the most expensive one.
+This helps finding the targets for manual memory sharing, or the threshold
+to use for smpi/auto-shared-malloc-thresh option (see :ref:`cfg=smpi/auto-shared-malloc-thresh`).
 
 .. _cfg=smpi/keep-temps:
 
@@ -1087,21 +1240,6 @@ profile your code. Indeed, the binary files are removed very early
 under the dlopen privatization schema, which tends to fool the
 debuggers.
 
-.. _cfg=smpi/lat-factor:
-
-Latency factors
-...............
-
-**Option** ``smpi/lat-factor`` |br|
-**default:** 65472:11.6436;15424:3.48845;9376:2.59299;5776:2.18796;3484:1.88101;1426:1.61075;732:1.9503;257:1.95341;0:2.01467
-
-The motivation and syntax for this option is identical to the motivation/syntax
-of :ref:`cfg=smpi/bw-factor`.
-
-There is an important difference, though: While smpi/bw-factor `reduces` the
-actual bandwidth (i.e., values between 0 and 1 are valid), latency factors
-increase the latency, i.e., values larger than or equal to 1 are valid here.
-
 .. _cfg=smpi/papi-events:
 
 Trace hardware counters with PAPI
@@ -1126,7 +1264,7 @@ It is planned to make this feature available on a per-process (or per-thread?) b
 The first draft, however, just implements a "global" (i.e., for all processes) set
 of counters, the "default" set.
 
-.. code-block:: shell
+.. code-block:: none
 
    --cfg=smpi/papi-events:"default:PAPI_L3_LDM:PAPI_L2_LDM"
 
@@ -1177,9 +1315,9 @@ This configuration option can only use either full paths to libraries,
 or full names.  Check with ldd the name of the library you want to
 use.  For example:
 
-.. code-block:: shell
+.. code-block:: console
 
-   ldd allpairf90
+   $ ldd allpairf90
       ...
       libgfortran.so.3 => /usr/lib/x86_64-linux-gnu/libgfortran.so.3 (0x00007fbb4d91b000)
       ...
@@ -1222,6 +1360,77 @@ Each collective operation can be manually selected with a
 .. TODO:: All available collective algorithms will be made available
           via the ``smpirun --help-coll`` command.
 
+.. _cfg=smpi/barrier-collectives:
+
+Add a barrier in all collectives
+................................
+
+**Option** ``smpi/barrier-collectives`` **default:** off
+
+This option adds a simple barrier in some collective operations to catch dangerous
+code that may or may not work depending on the MPI implementation: Bcast, Exscan,
+Gather, Gatherv, Scan, Scatter, Scatterv and Reduce.
+
+For example, the following code works with OpenMPI while it deadlocks in MPICH and
+Intel MPI. Broadcast seem to be "fire and forget" in OpenMPI while other
+implementations expect to receive a message.
+
+.. code-block:: C
+
+  if (rank == 0) {
+    MPI_Bcast(buf1, buff_size, MPI_CHAR, 0, newcom);
+    MPI_Send(&buf2, buff_size, MPI_CHAR, 1, tag, newcom);
+  } else if (rank==1) {
+    MPI_Recv(&buf2, buff_size, MPI_CHAR, 0, tag, newcom, MPI_STATUS_IGNORE);
+    MPI_Bcast(buf1, buff_size, MPI_CHAR, 0, newcom);
+  }
+
+The barrier is only simulated and does not involve any additional message (it is a S4U barrier).
+This option is disabled by default, and activated by the `-analyze` flag of smpirun.
+
+.. _cfg=smpi/barrier-finalization:
+
+Add a barrier in MPI_Finalize
+.............................
+
+**Option** ``smpi/finalization-barrier`` **default:** off
+
+By default, SMPI processes are destroyed as soon as soon as their code ends,
+so after a successful MPI_Finalize call returns. In some rare cases, some data
+might have been attached to MPI objects still active in the remaining processes,
+and can be destroyed eagerly by the finished process.
+If your code shows issues at finalization, such as segmentation fault, triggering
+this option will add an explicit MPI_Barrier(MPI_COMM_WORLD) call inside the
+MPI_Finalize, so that all processes will terminate at almost the same point.
+It might affect the total timing by the cost of a barrier.
+
+.. _cfg=smpi/errors-are-fatal:
+
+Disable MPI fatal errors
+........................
+
+**Option** ``smpi/errors-are-fatal`` **default:** on
+
+By default, SMPI processes will crash if a MPI error code is returned. MPI allows
+to explicitely set MPI_ERRORS_RETURN errhandler to avoid this behaviour. This flag
+will turn on this behaviour by default (for all concerned types and errhandlers).
+This can ease debugging by going after the first reported error.
+
+.. _cfg=smpi/pedantic:
+
+Disable pedantic MPI errors
+...........................
+
+**Option** ``smpi/pedantic`` **default:** on
+
+By default, SMPI will report all errors it finds in MPI codes. Some of these errors
+may not be considered as errors by all developers. This flag can be turned off to
+avoid reporting some usually harmless mistakes.
+Concerned errors list (will be expanded in the future):
+
+ - Calling MPI_Win_fence only once in a program, hence just opening an epoch without
+   ever closing it.
+
 .. _cfg=smpi/iprobe:
 
 Inject constant times for MPI_Iprobe
@@ -1289,7 +1498,7 @@ values, for example ``1:3:2;10:5:1``.  The sections are divided by ";"
 so this example contains two sections.  Furthermore, each section
 consists of three values.
 
-1. The first value denotes the minimum size for this section to take effect;
+1. The first value denotes the minimum size in bytes for this section to take effect;
    read it as "if message size is greater than this value (and other section has a larger
    first value that is also smaller than the message size), use this".
    In the first section above, this value is "1".
@@ -1372,7 +1581,7 @@ of the SMPI CourseWare (see Activity #2.2 of the pointed
 assignment). In practice, change the calls for malloc() and free() into
 SMPI_SHARED_MALLOC() and SMPI_SHARED_FREE().
 
-SMPI provides two algorithms for this feature. The first one, called 
+SMPI provides two algorithms for this feature. The first one, called
 ``local``, allocates one block per call to SMPI_SHARED_MALLOC()
 (each call site gets its own block) ,and this block is shared
 among all MPI ranks.  This is implemented with the shm_* functions
@@ -1382,7 +1591,7 @@ for each shared block.
 With the ``global`` algorithm, each call to SMPI_SHARED_MALLOC()
 returns a new address, but it only points to a shadow block: its memory
 area is mapped on a 1 MiB file on disk. If the returned block is of size
-N MiB, then the same file is mapped N times to cover the whole bloc.
+N MiB, then the same file is mapped N times to cover the whole block.
 At the end, no matter how many times you call SMPI_SHARED_MALLOC, this will
 only consume 1 MiB in memory.
 
@@ -1409,16 +1618,34 @@ entry per MB of malloced data instead of one entry per 4 kB.
 To activate this, you must mount a hugetlbfs on your system and allocate
 at least one huge page:
 
-.. code-block:: shell
+.. code-block:: console
 
-    mkdir /home/huge
-    sudo mount none /home/huge -t hugetlbfs -o rw,mode=0777
-    sudo sh -c 'echo 1 > /proc/sys/vm/nr_hugepages' # echo more if you need more
+    $ mkdir /home/huge
+    $ sudo mount none /home/huge -t hugetlbfs -o rw,mode=0777
+    $ sudo sh -c 'echo 1 > /proc/sys/vm/nr_hugepages' # echo more if you need more
 
 Then, you can pass the option
 ``--cfg=smpi/shared-malloc-hugepage:/home/huge`` to smpirun to
 actually activate the huge page support in shared mallocs.
 
+.. _cfg=smpi/auto-shared-malloc-thresh:
+
+Automatically share allocations
+...............................
+
+**Option** ``smpi/auto-shared-malloc-thresh:`` **Default:** 0 (false)
+   This value in bytes represents the size above which all allocations
+   will be "shared" by default (as if they were performed through
+   SMPI_SHARED_MALLOC macros). Default = 0 = disabled feature.
+   The value must be carefully chosen to only select data buffers which
+   will not modify execution path or cause crash if their content is false.
+   Option :ref:`cfg=smpi/display-allocs` can be used to locate the largest
+   allocation detected in a run, and provide a good starting threshold.
+   Note : malloc, calloc and free are overridden by smpicc/cxx by default.
+   This can cause some troubles if codes are already overriding these. If this
+   is the case, defining SMPI_NO_OVERRIDE_MALLOC in the compilation flags can
+   help, but will make this feature unusable.
+
 .. _cfg=smpi/wtime:
 
 Inject constant times for MPI_Wtime, gettimeofday and clock_gettime
@@ -1450,6 +1677,16 @@ to be broken out of and reset each time your code asks for the current time.
 If the simulation speed really matters to you, you can avoid this
 extra delay by setting smpi/wtime to 0.
 
+.. _cfg=smpi/list-leaks:
+
+Report leaked MPI objects
+.........................
+
+**Option** ``smpi/list-leaks`` **default:** 0
+
+This option controls whether to report leaked MPI objects.
+The parameter is the number of leaks to report.
+
 Other Configurations
 --------------------
 
@@ -1489,12 +1726,12 @@ reaches the given time, a SIGTRAP is raised.  This can be used to stop
 the execution and get a backtrace with a debugger.
 
 It is also possible to set the breakpoint from inside the debugger, by
-writing in global variable simgrid::simix::breakpoint. For example,
+writing in global variable simgrid::kernel::cfg_breakpoint. For example,
 with gdb:
 
-.. code-block:: shell
+.. code-block:: none
 
-   set variable simgrid::simix::breakpoint = 3.1416
+   set variable simgrid::kernel::cfg_breakpoint = 3.1416
 
 .. _cfg=debug/verbose-exit:
 
@@ -1522,10 +1759,122 @@ the tests: the full file path would makes the tests non-reproducible because
 the paths of source files depend of the build settings. That would
 break most of the tests since their output is continually compared.
 
-Logging Configuration
+.. _logging_config:
+
+Logging configuration
 ---------------------
 
-This can be done by using XBT. Go to :ref:`XBT_log` for more details.
+As introduced in :ref:`outcome_logs`, the SimGrid logging mechanism allows to configure at runtime the messages that should be displayed and those that should be omitted. Each
+message produced in the code is given a category (denoting its topic) and a priority. Then at runtime, each category is given a threshold (only messages of priority higher than
+that threshold are displayed), a layout (deciding how the messages in this category are formatted), and an appender (deciding what to do with the message: either print on stderr or
+to a file).
+
+This section explains how to configure this logging features. You can also refer to the documentation of the :ref:`programmer's interface <logging_prog>`, that allows to produce
+messages from your code.
+
+Most of the time, the logging mechanism is configured at runtime using the ``--log`` command-line argument, even if you can also use :c:func:`xbt_log_control_set()` to control it from
+your program. To pass configure more than one setting, you can either pass several ``--log`` arguments, or separate your settings with spaces, that must be quoted accordingly. In
+practice, the following is equivalent to the above settings: ``--log=root.thresh:error --log=s4u_host.thresh:debug``.
+
+If you want to specify more than one setting, you can either pass several ``--log`` argument to your program as above, or separate them with spaces. In this case, you want to quote
+your settings, as in ``--log="root.thresh:error s4u_host.thresh:debug"``. The parameters are interpreted in order, from left to right.
+
+
+Threshold configuration
+.......................
+
+The keyword ``threshold`` controls which logging event will get displayed in a given category. For example, ``--log=root.threshold:debug`` displays *every* message produced in the
+``root`` category and its subcategories (i.e., every message produced -- this is *extremely* verbose), while ``--log=root.thres:critical`` turns almost everything off. As you can
+see, ``threshold`` can be abbreviated here.
+
+Existing thresholds:
+
+ - ``trace`` some functions display a message at this level when entering or returning
+ - ``debug`` output that is mostly useful when debugging the corresponding module.
+ - ``verbose`` verbose output that is only mildly interesting and can easily be ignored
+ - ``info`` usual output (this is the default threshold of all categories)
+ - ``warning`` minor issue encountered
+ - ``error`` issue encountered
+ - ``critical`` major issue encountered, such as assertions failures
+
+.. _log/fmt:
+
+Format configuration
+....................
+
+The keyword ``fmt`` controls the layout (the format) of a logging category. For example, ``--log=root.fmt:%m`` reduces the output to the user-message only, removing any decoration such
+as the date, or the actor ID, everything. Existing format directives:
+
+ - %%: the % char
+ - %n: line separator (LOG4J compatible)
+ - %e: plain old space (SimGrid extension)
+
+ - %m: user-provided message
+
+ - %c: Category name (LOG4J compatible)
+ - %p: Priority name (LOG4J compatible)
+
+ - %h: Hostname (SimGrid extension)
+ - %a: Actor name (SimGrid extension -- note that with SMPI this is the integer value of the process rank)
+ - %i: Actor PID (SimGrid extension -- this is a 'i' as in 'i'dea)
+ - %t: Thread "name" (LOG4J compatible -- actually the address of the thread in memory)
+
+ - %F: file name where the log event was raised (LOG4J compatible)
+ - %l: location where the log event was raised (LOG4J compatible, like '%%F:%%L' -- this is a l as in 'l'etter)
+ - %L: line number where the log event was raised (LOG4J compatible)
+ - %M: function name (LOG4J compatible -- called method name here of course).
+
+ - %d: date (UNIX-like epoch)
+ - %r: application age (time elapsed since the beginning of the application)
+
+
+``--log=root.fmt:'[%h:%a:(%i) %r] %l: %m%n'`` gives you the default layout used for info messages while ``--log=root.fmt:'[%h:%a:(%i) %r] %l: [%c/%p] %m%n'`` gives you the default
+layout for the other priorities (it adds the source code location). Also, the actor identification is omitted by the default layout for the messages coming directly from the
+SimGrid kernel, so info messages are formatted with ``[%r] [%c/%p] %m%n`` in this case. When specifying the layout manually, such distinctions are currently impossible, and the
+provided layout is used for every messages.
+
+As with printf, you can specify the precision and width of the fields. For example, ``%.4r`` limits the date precision to four digits while ``%15h`` limits the host name to at most
+15 chars.
+
+
+If you want to have spaces in your log format, you should protect it. Otherwise, SimGrid will consider that this is a space-separated list of several parameters. But you should
+also protect it from the shell that also splits command line arguments on spaces. At the end, you should use something such as ``--log="'root.fmt:%l: [%p/%c]: %m%n'"``.
+Another option is to use the ``%e`` directive for spaces, as in ``--log=root.fmt:%l:%e[%p/%c]:%e%m%n``.
+
+Category appender
+.................
+
+The keyword ``app`` controls the appended of a logging category. For example ``--log=root.app:file:mylogfile`` redirects every output to the file ``mylogfile``.
+
+With the ``splitfile`` appender, a new file is created when the size of the output reaches the specified size. The format is ``--log=root.app:splitfile:<size>:<file name>``. For
+example, ``--log=root.app:splitfile:500:mylog_%`` creates log files of at most 500 bytes, using the names ``mylog_0``, ``mylog_1``, ``mylog_2``, etc.
+
+The ``rollfile`` appender uses one file only, but the file is emptied and recreated when its size reaches the specified maximum. For example, ``--log=root.app:rollfile:500:mylog``
+ensures that the log file ``mylog`` will never overpass 500 bytes in size.
+
+Any appender setup this way have its own layout format, that you may change afterward. When specifying a new appender, its additivity is set to false to prevent log event displayed
+by this appender to "leak" to any other appender higher in the hierarchy. You can naturally change that if you want your messages to be displayed twice.
+
+Category additivity
+...................
+
+The keyword ``add`` controls the additivity of a logging category. By default, the messages are only passed one appender only: the more specific, i.e. the first one found when
+climbing the tree from the category in which they were produced. In Log4J parlance, it is said that the default additivity of appenders is false. If you change this setting to
+``on`` (or ``yes`` or ``1``), the produced messages will also be passed to the upper appender.
+
+Let's consider a more complex example: ``--log="root.app:file:all.log s4u.app:file:iface.log xbt.app:file:xbt.log xbt.add:yes``. Here, the logging of s4u will be sent to the
+``iface.log`` file; the logging of the xbt toolbox will be sent to both the ``xbt.log`` file and the ``all.log`` file (because xbt additivity was enabled); and every other loggings
+will only be sent to ``all.log``.
+
+Other options
+.............
+
+``--help-logs`` displays a complete help message about logging in SimGrid.
+
+``--help-log-categories`` displays the actual hierarchy of log categories for this binary.
+
+``--log=no_loc`` hides the source locations (file names and line numbers) from the messages. This is useful to make tests reproducible.
+
 
 .. |br| raw:: html