.. release_notes:
-Release Notes
-=============
+SimGrid 4 Release Notes
+=======================
This page gathers some release notes, to shed light on the recent and current development of SimGrid.
+Version 3.12 was the last pure release of SimGrid 3 while all versions starting with v3.13 can be seen as usable pre-versions of SimGrid 4.
Ancient versions are not documented here (the project started in 1998), but in the ChangeLog file only.
Version 3.13 (Apr 27. 2016)
The Half Release, a.k.a. the Zealous Easter Trim:
- * Half of the lines of code are gone.
+.. rst-class:: compact-list
- * v3.12: 286k lines; v3.13: 142k lines (+ comments)
- * Experimental untested unused "features" removed
- * We rewrote several parts in C++ instead of C
+ * Remove half of the lines of code: v3.12 was 286k lines while v3.13 is only 142k lines. |br|
+ Experimental untested unused "features" removed, and several parts were rewritten from C to C++.
- * Introducing v4 of the XML platform format (many long-due cleanups)
- * MSG examples fully reorganized (in C and Java)
- * The S4U interface is rising, toward SimGrid 4
-
- * All host manipulations now done in S4U
- * SimDag was mostly rewritten on top of S4U
- * MSG & SimDag interfaces mostly unchanged
+ * Introducing v4 of the XML platform format (many long-due cleanups)
+ * MSG examples fully reorganized (in C and Java)
+ * The S4U interface is rising, toward SimGrid 4:|br| All host manipulations now done in S4U,
+ SimDag was mostly rewritten on top of S4U but MSG & SimDag interfaces mostly unchanged.
Version 3.14 (Dec 25. 2016)
---------------------------
These changes should be transparent to the users of the MSG, SMPI and SimDag interfaces, even if some buggy features were reworked
while some new features were added.
-Users are expected to switch to this new version at their own pace, as we do not have the manpower to do any bugfixing on the old releases.
+Users are expected to switch to this new version at their own pace, as we do not have the manpower to do any bug fixing on the old releases.
This version was tested on several Linux distributions, Mac OSX, Windows (restricted to the Java bindings when not using the Ubuntu
subsystem of Win10), FreeBSD and NetBSD.
Main changes:
- * Documentation reorganized and improved
- * S4U interface further rising, toward SimGrid 4
-
- - Routing code rewritten for readability
- - Virtual Machines almost turned into a plugin
- - MSG, SimDag, MPI interfaces mostly unchanged
+.. rst-class:: compact-list
- * The model-checker now works on NetBSD too.
+ * Documentation reorganized and improved
+ * S4U interface further rising, toward SimGrid 4: |br|
+ Routing code rewritten for readability; Virtual Machines almost turned into a plugin; MSG, SimDag, MPI interfaces mostly unchanged.
+ * The model-checker now works on NetBSD too.
Version 3.14.159 (Dec 29. 2016)
-------------------------------
The Spring Release: continuous integration servers become green.
- * S4U: progress, integrating more parts of SimDag; New examples.
- * SMPI: Support MPI 2.2; Convert internals to C++ (TBC).
- * Java: Massive memleaks and performance issues fixed.
- * Plus the usual bug fixes, cleanups and documentation improvements.
+.. rst-class:: compact-list
-Users are expected to switch to this new version at their own pace, as we do not have the manpower to do any bugfixing on the old releases.
+ * S4U: progress, integrating more parts of SimDag; New examples.
+ * SMPI: Support MPI 2.2; Convert internals to C++ (TBC).
+ * Java: Massive memleaks and performance issues fixed.
+ * Plus the usual bug fixes, cleanups and documentation improvements.
+
+Users are expected to switch to this new version at their own pace, as we do not have the manpower to do any bug fixing on the old releases.
This version was tested on several Linux distributions, Mac OSX, Windows (restricted to our Java bindings), FreeBSD and NetBSD.
None of our 600+ integration tests is known to fail on any of these.
The Blooming Spring Release: developments are budding.
- * S4U: Progress; Activity refcounting is now automatic.
- * XML: <AS> can now be named <zone> as they should.
- * SMPI: Further performance improvements; RMA support.
- * Cloud: Multi-core VMs (do not overcommit them yet)
- * (+ bug fixes, cleanups and documentation improvements)
+.. rst-class:: compact-list
+
+ * S4U: Progress; Activity refcounting is now automatic.
+ * XML: <AS> can now be named <zone> as they should.
+ * SMPI: Further performance improvements; RMA support.
+ * Cloud: Multi-core VMs (do not overcommit them yet)
+ * (+ bug fixes, cleanups and documentation improvements)
SMPI performance was further improved, using various OS-level magic to speed up our virtualization of the MPI code to be run. This allowed
Tom to run a simulation of HPL involving 10^6 processes... Wow. The dlopen privatization schema should even allows to run your ranks
On the Cloud side, we implemented multi-core VMs, which naturally acts as containers of processes;
S4U, the future interface of SimGrid 4.0 also progressed quite a bit.
-The Storage is currently cleaned up by Fred, and some API changes are to be expected. We are sorry but the exisiting API is so crappy that
+The Storage is currently cleaned up by Fred, and some API changes are to be expected. We are sorry but the existing API is so crappy that
nobody ever used it, I guess. If you need it, please speak up soon!
We renamed AS into NetZone in the XML files (but the old one still work so no rush to update your platform). Since our platforms are
hierarchical, it makes no sense to name our zones "Autonomous Systems". Some other documentation pages got updated and modified. If
you see a particularly old, misleading or otherwise ugly doc page, please tell us and we'll fix it. Even typo reports are welcome.
-But most of the work on S4U is not directly visible from the user. We rewamped the whole code of activities (comms, execs, mutex, etc) to
+But most of the work on S4U is not directly visible from the user. We revamped the whole code of activities (comms, execs, mutex, etc) to
not mix the applicative logic (calling test() or wait()) with the object refcounting. Now, you can test your comm object as many time as
you want. This change was really intrusive in our internals, and we're not done with restabilizing every bits, but we're on it.
Still on the S4U front, we managed to remove a few more XBT modules. We prefer to use the std or boost libraries nowadays, and switching
-away from the XBT module enable to reduce our maintainance burden. Be warned that XBT will not always remain included in SimGrid.
+away from the XBT module enable to reduce our maintenance burden. Be warned that XBT will not always remain included in SimGrid.
On the infrastructure side, we are trying to setup a regular build task for the main projects using SimGrid, to check that our changes
don't break them. The one of StarPU is close to be working (even if not completely). If you want to have your own code tested regularly
In addition, the future already started. We have ongoing changesets that were not ready for 3.16 but should be part of 3.17:
- - Energy modeling for the network too
- - New reduction algorithm for the model-checker, based on event folding structures
- - Multi-model simulations, to specify a differing networking model for each netzone.
+.. rst-class:: compact-list
+
+ - Energy modeling for the network too
+ - New reduction algorithm for the model-checker, based on event folding structures
+ - Multi-model simulations, to specify a differing networking model for each netzone.
Version 3.17 (Oct 8. 2017)
--------------------------
This version is dubbed the "The Drained Leaks release", because almost no known memleak remains, despite testing.
- * Many many internal cleanups (almost 700 commits since 3.16).
- * The coverage of our tests is above 80%.
- * All memleaks but one plugged; A dozen of bugs fixed.
- * XBT: Further replace XBT with std::* constructs.
+.. rst-class:: compact-list
+
+ * Many many internal cleanups (almost 700 commits since 3.16).
+ * The coverage of our tests is above 80%.
+ * All memleaks but one plugged; A dozen of bugs fixed.
+ * XBT: Further replace XBT with std::* constructs.
Version 3.18 (Dec. 24 2017)
---------------------------
Main changes in the "Ho Ho Ho! SimGrid 4 beta is coming to town" release:
- * Convert almost all interesting MSG examples to S4U.
- * New model: energy consumption due to the network.
- * Major cleanups in the disk and storage subsystems.
- * (+ further deprecate XBT, bug fixes and doc improvement)
+.. rst-class:: compact-list
+
+ * Convert almost all interesting MSG examples to S4U.
+ * New model: energy consumption due to the network.
+ * Major cleanups in the disk and storage subsystems.
+ * (+ further deprecate XBT, bug fixes and doc improvement)
SimGrid 4 *may* be there by the next solstice.
In total, this "Moscovitly-cold Spring" release brings more than 500 commits made by 7 individuals over the last 3 months.
- * SMPI: Allow to start new actors and ranks after simulation start.
- * SMPI: Support ICC, better testing on classical proxy apps.
- * Some kernel headers are now installed, allowing external plugins.
- * (+ the classical bug fixes and doc improvement)
+.. rst-class:: compact-list
+
+ * SMPI: Allow to start new actors and ranks after simulation start.
+ * SMPI: Support ICC, better testing on classical proxy apps.
+ * Some kernel headers are now installed, allowing external plugins.
+ * (+ the classical bug fixes and doc improvement)
Version 3.19.1 (March 22. 2018)
-------------------------------
SimGrid4: Existing interfaces remain unchanged, but the new S4U interface is budding and the internals are deeply reorganized.
Since 2015, we work hard to reduce the changes to public APIs. When we need to rename a public library symbol in S4U, we let your compiler
-issue an explicative warning when you use the deprecated function. These messages remain for four releases, i.e. for one full year,
+issue an explicit warning when you use the deprecated function. These messages remain for four releases, i.e. for one full year,
before turning into an error. Starting with v3.15, your can also adapt to API changes with the SIMGRID_VERSION macro, that is defined to
31500 for v3.15, to 31901 for v3.19.1 and so on.
Starting with this v3.19.1, our commitment to reduce the changes to the public interfaces is extended from the API to the ABI: a program
-using only MSG or SimDag and compiled against a given version of simgrid can probably be used with a later version of SimGrid without
-recompilation. We will do our best... but don't expect too much of it, that's a really difficult goal during such profund refactoring.
+using only MSG or SimDag and compiled against a given version of SimGrid can probably be used with a later version of SimGrid without
+recompilation. We will do our best... but don't expect too much of it, that's a really difficult goal during such profound refactoring.
The difference between v3.19 and v3.19.1 is that the former was accidentally breaking the ABI of MSG, while the later is restoring the
previous ABI.
Once the S4U interface stabilizes, we will provide C bindings on top of it, along with Java and Python ones. Maybe in 3.21 or 3.22.
All this is not contradictory with the fact that MSG as a whole is deprecated, because this deprecation only means that new projects
-should go for MSG but for S4U (to benefit of the future). Despite this deprecation, old MSG projects should still be usable with no change,
-if we manage to. This is a matter of scientific reproducibility to us.
+should go for S4U instead of MSG to benefit of the future. Despite this deprecation, old MSG projects should still be usable with no
+change, if we manage to. This is a matter of scientific reproducibility to us.
Version 3.20 (June 25 2018)
---------------------------
The robustness of SMPI continues to improve. It was rock stable, and you can now use it to move the world (if your lever is long enough).
We now use several full-scale projects as nightly integration tests: StarPU, BigDFT and also 45 Proxy Apps from various collections.
-https://github.com/simgrid/SMPI-proxy-apps/
+https://framagit.org/simgrid/SMPI-proxy-apps
Main changes in the "proxy snake_case()" release are:
- * Sanitize the public API. Compatibility wrappers in place for one year.
- * More CI: ~45 Proxy Apps + BigDFT + StarPU now tested nightly
- * MPI: Port the trace replay engine to C++, fix visualization
- * (+ the classical bug fixes and doc improvement)
+.. rst-class:: compact-list
+
+ * Sanitize the public API. Compatibility wrappers in place for one year.
+ * More CI: ~45 Proxy Apps + BigDFT + StarPU now tested nightly
+ * MPI: Port the trace replay engine to C++, fix visualization
+ * (+ the classical bug fixes and doc improvement)
Version 3.21 (October 5. 2018)
------------------------------
Main changes of The Restarting Documentation (TRD) release:
- * Start to overhaul the documentation, and move to Sphinx + RTD.
- * Allow dynamic replay of MPI apps, controlled by S4U actors
- * Rewrite the support for auto-restarted actors (was utterly broken)
- * (+ the classical bug fixes and doc improvement)
+.. rst-class:: compact-list
+
+ * Start to overhaul the documentation, and move to Sphinx + RTD.
+ * Allow dynamic replay of MPI apps, controlled by S4U actors
+ * Rewrite the support for auto-restarted actors (was utterly broken)
+ * (+ the classical bug fixes and doc improvement)
Version 3.22 (April 2. 2019)
----------------------------
-The Easter Christmas Release. It was expected from Chrismas, but I was so late that I even managed to miss the spring deadline.
+The Easter Christmas Release. It was expected from Christmas, but I was so late that I even managed to miss the spring deadline.
This started to be a running joke, so I decided to release it for April 1. But I'm even late for this... Sorry :)
- * Introducing the Python bindings (still beta)
- * Doc: SMPI tutorial and platform description ported to RTD
- * Many internal cleanups leading to some user-level speedups
- * (+ the classical bug fixes and internal refactorings)
+.. rst-class:: compact-list
+
+ * Introducing the Python bindings (still beta)
+ * Doc: SMPI tutorial and platform description ported to RTD
+ * Many internal cleanups leading to some user-level speedups
+ * (+ the classical bug fixes and internal refactorings)
The most visible change is certainly the new Python bindings. They are rather experimental yet, and their API may change a bit in future
release, but you are already welcome to test them. Many examples are now also available in Python, and the missing ones are on their way.
for the existing users). Their examples are now hidden in deprecated/ Please switch to S4U if you like C++ or to Python if not.
This new version also introduce a heavy load of internal cleanups. Fred converted more internals to real C++, with more classes and less
-procedural cruft. Henri and the other Wrench developpers reported many bugs around activity canceling and resource failures, and we fixed
+procedural cruft. Henri and the other Wrench developers reported many bugs around activity canceling and resource failures, and we fixed
quite a bit of them, but many dark snakes remain in that lake. Fred and Martin converted more doc to the new system (the platform chapter
is not finished, but it's not worse than the old one either) while Augustin completed the tutorial for MPI applications. Augustin also
added several non-blocking collectives to SMPI, even if Martin finally decided to release right before he could complete the last ones
Main change in the "Exotic Solstice" Release:
- * Support for Solaris and Haiku OSes. Just for fun :)
- * SMPI: more of MPI3.1; some MPI/IO and async collectives.
- * Python bindings can now be installed from pip.
- * (+ many many bug fixes and internal refactorings)
+.. rst-class:: compact-list
+
+ * Support for Solaris and Haiku OSes. Just for fun :)
+ * SMPI: more of MPI3.1; some MPI/IO and async collectives.
+ * Python bindings can now be installed from pip.
+ * (+ many many bug fixes and internal refactorings)
Version 3.24 (October 10. 2019)
-------------------------------
This is the Clean Disk Release:
- * Introduce an experimental Wifi network model.
- * Introduce <disk> (cleaner logic than <storage>).
- * SMPI: Implement Errhandlers and some more MPI3.1 calls.
- * (+ many bug fixes and internal refactorings)
+.. rst-class:: compact-list
+
+ * Introduce an experimental Wifi network model.
+ * Introduce <disk> (cleaner logic than <storage>).
+ * SMPI: Implement Errhandlers and some more MPI3.1 calls.
+ * (+ many bug fixes and internal refactorings)
Since June, we continued our new release schema: v3.23.2 got released at some point as an interim release for people wanting something
between stable releases (tested on many systems but coming at most once per quarter) and git version (almost always working but you never
version number: v3.23.1 then 3.23.3 until yesterday, and soon 3.24.1.
As a user, there is no urgency to upgrade, even if you should not wait more than 9 months to upgrade to another stable version: our policy is
-to keep backward compatibility and nice upgrading pathes for 3 stable versions. v3.24 removes symbols that got deprecated in v3.20, last
+to keep backward compatibility and nice upgrading patches for 3 stable versions. v3.24 removes symbols that got deprecated in v3.20, last
year. It deprecates things that will continue to work until v3.27.
Speaking of deprecation, we would like to hear from you if you are using the Java bindings under Windows without the WSL installed.
Version 3.25 (Feb 2. 2020)
--------------------------
-This is the "Palindrom Day" release (today is 02 02 2020).
+This is the "Palindrome Day" release (today is 02 02 2020).
-* Improve the Python usability (stability and documentation).
+.. rst-class:: compact-list
- - A nasty synchronization bug was ironed out, see full changelog.
- - Python's doc now integrated with C++ (was organized as a separate tree).
- - C bindings of S4U were not even part of the doc.
- - The C++ doc was also improved as methods are now split by theme.
- - See https://simgrid.org/doc/latest/app_s4u.html#api-reference
+ * Improve the Python usability (stability and documentation). |br|
+ A nasty synchronization bug (due to a bad handling of the GIL) was ironed out, so that no known bug remains in Python examples.
+ The Python documentation is now integrated with the C++ one, also along with the C bindings that were previously not documented.
+ The API documentation is now split by theme in the hope to keep it readable.
-* Further deprecate MSG: you now have to pass -Denable_msg=ON to cmake.
+ * Further deprecate MSG: you now have to pass -Denable_msg=ON to cmake. |br|
+ This is OFF by default (also disabling the Java API that is still based on MSG).
+ The plan is to completely remove MSG by 2020Q4 or 2021Q1.
- - This is mandatory to use the Java bindings.
- - OFF by default; The plan is to completely remove MSG by 2020Q4 or 2021Q1.
-
-* SimDAG++: Automatic dependencies on S4U activities (experimental)
-
- - Some features are already implemented but not all of them
- - Cannot block an activity until it's scheduled on a resource
- - No heterogeneous wait_any() that would mix Exec/Comm/Io activities.
- - See examples/s4u/{io,exec,comm}-dependent for what's already there.
+ * SimDAG++: Automatic dependencies on S4U activities (experimental). |br|
+ This implements some features of SimDAG within S4U, but not all of them: you cannot block an activity until it's scheduled on a resource
+ and there is no heterogeneous wait_any() that would mix Exec/Comm/Io activities. See ``examples/s4u/{io,exec,comm}-dependent`` for what's already there.
Since last fall, we continued to push toward the future SimGrid4 release. This requires to remove MSG and SimDAG once all users have
-migrated to S4U. The two old interfaces are still here, but this release gives another gentle incitative toward the migration. You now
+migrated to S4U. The two old interfaces are still here, but this release gives another gentle incentive toward the migration. You now
have to explicitly ask for MSG to be compiled in (and it may be removed by Q42020 or Q12021 along with the current Java bindings), and
this release proposes a nice S4U replacement for some parts of SimDAG.
To celebrate the ease of the lockdown in France, we decided to bring another version of SimGrid to the world.
This is the "Release" release. Indeed a small contribution to the event, but this release was long overdue anyway.
- * SMPI: improved support of the proxy apps (including those using petsc)
- * WiFi: easier description in XML; energy plugin; more examples.
- * ns-3: Many bug fixes, can use the wifi models too.
- * (+ many bug fixes, documentation improvement and internal refactoring)
+.. rst-class:: compact-list
+
+ * SMPI: improved support of the proxy apps (including those using petsc)
+ * WiFi: easier description in XML; energy plugin; more examples.
+ * ns-3: Many bug fixes, can use the wifi models too.
+ * (+ many bug fixes, documentation improvement and internal refactoring)
Version 3.27 (March 29. 2021)
-----------------------------
To celebrate the 1176th anniversary of the siege of Paris by Vikings in 845, we just released another version of SimGrid, the Ragnar Release.
Yeah, that's a stupid release name, but we already had 4 "spring release" in the past, so we needed another name.
- * SMPI: can now report leaks and hint about the mallocs and kernels hindering simulation scalability
- * Doc: Several new sections in the user manual, and start documenting the internals.
- * S4U: Direct comms from host to host, without mailboxes.
+.. rst-class:: compact-list
+
+ * SMPI: can now report leaks and hint about the mallocs and kernels hindering simulation scalability.
+ * Doc: Several new sections in the user manual, and start documenting the internals.
+ * S4U: Direct comms from host to host, without mailboxes.
In some sense, these changes are just the tip of the iceberg, as we had many refactoring and internal cleanups in this release cycle too. Actually, we have 3
main ongoing refactoring that should bring us closer to SimGrid4, that will eventually occur.
To celebrate the birthday of Crown Princess Victoria, we just released another version of SimGrid, the "Victoriadagarna" release.
- * Programmatic platform description (only C++ for now).
- * New plugin to simplify producer/consumer applications.
- * MC: new tutorial and associated docker image.
- * SMPI: improve error handling for incorrect advanced usages.
- * Many internal cleanups and refactoring to prepare the future.
+.. rst-class:: compact-list
+
+ * Programmatic platform description (only C++ for now).
+ * New plugin to simplify producer/consumer applications.
+ * MC: new tutorial and associated docker image.
+ * SMPI: improve error handling for incorrect advanced usages.
+ * Many internal cleanups and refactoring to prepare the future.
As usual, even the full changelog is only the tip of the iceberg, given the amount of changes in the backstage.
`Stack Overflow <https://stackoverflow.com/questions/tagged/simgrid>`_,
or using the `issues tracker <https://framagit.org/simgrid/simgrid/-/issues>`_.
- * Python bindings for the platform creation API
- * Introduce non-linear resource sharing, allowing decay models
- * New documentation section on realistic I/O modeling
- * (+ many bug fixes and internal refactoring)
+.. rst-class:: compact-list
+
+ * Python bindings for the platform creation API
+ * Introduce non-linear resource sharing, allowing decay models
+ * New documentation section on realistic I/O modeling
+ * (+ many bug fixes and internal refactoring)
This release finishes the work on programmatic platforms, that was ongoing since 3.27. It is now possible to define a complete platform in either C++
or python, and the XML approach is now deprecated. It will probably remain around for a long time, but no evolution is planned. New features will not
This release also paves the way for new models, with the introduction of two new features to the model solver:
- * Non-linear resource sharing was introduced, allowing to model resource whose performance heavily degrades with contention. This may be used in the
- future for Wi-Fi links, where the total amount of data exchanged in a cell drops when the amount of stations reaches a threshold.
- * Dynamic factors model variability in the speed of activities. This can be used to model an overhead (e.g., there is a 20 bytes header in a 480
- bytes TCP packet so the factor 0.9583) but the novelty is this factor can now easily be adjusted depending on activity's and resources
- characteristics.
+.. rst-class:: compact-list
- This existed for network (e.g., the effective bandwidth depends on the message in SMPI piecewise-linear network model) but it is now more general
- (the factor may depend on the source and destination and thus account to different behaviors for intra-node communications and extra-node
- communications) and is available for CPUs (e.g., if you want to model an affinity as in the "Unrelated Machines" problem in scheduling) and disks
- (e.g., if you want to model a stochastic capacity) too.
-
- The same mechanism is also available for the latency, which allows to easily introduce complex variability patterns.
+ * Non-linear resource sharing was introduced, allowing to model resource whose performance heavily degrades with contention. This may be used in the
+ future for Wi-Fi links, where the total amount of data exchanged in a cell drops when the amount of stations reaches a threshold.
+ * Dynamic factors model variability in the speed of activities. This can be used to model an overhead (e.g., there is a 20 bytes header in a 480
+ bytes TCP packet so the factor 0.9583) but the novelty is this factor can now easily be adjusted depending on activity's and resources
+ characteristics. |br|
+ This existed for network (e.g., the effective bandwidth depends on the message in SMPI piecewise-linear network model) but it is now more general
+ (the factor may depend on the source and destination and thus account to different behaviors for intra-node communications and extra-node
+ communications) and is available for CPUs (e.g., if you want to model an affinity as in the "Unrelated Machines" problem in scheduling) and disks
+ (e.g., if you want to model a stochastic capacity) too. |br|
+ The same mechanism is also available for the latency, which allows to easily introduce complex variability patterns.
These new features are not used yet in the provided models, but this will probably change in future releases.
Version 3.30 (January 30. 2022)
----------------------------
+-------------------------------
The Sunday Bloody Sunday release.
that can prevent an activity to start. The underlying idea was to be able to manage application DAGs, a la SimDag, through the S4U API, and have
maestro to handle the execution of such DAGs.
-This release finishes this work, which is presented in a new set of examples (`examples/cpp/dag-*`). The direct consequences on the code base of this
+This release finishes this work, which is presented in a new set of examples (``examples/cpp/dag-*``). The direct consequences on the code base of this
new feature are:
* The SimDag API for the simulation of the scheduling of Directed Acyclic Graphs has been finally dropped. It was marked as deprecated for a couple
is still possible through the regular instrumentation API based on the Paje format.
On the bindings front, we dropped the Lua bindings to create new platforms, as the C++ and Python interfaces are much better to that extend.
-Also, the algorithm tutorial can now be taken in Python, for those of you alergic to C++.
+Also, the algorithm tutorial can now be taken in Python, for those of you allergic to C++.
+
+Finally, on the SMPI front, we introduced a :ref:`new documentation section <models_calibration>` on calibrating the SMPI models from your
+measurements and fixed some issues with the replay mechanism.
+
+Version 3.31 (not released yet)
+-------------------------------
-Finally, on the SMPI front, we introduced a new documentation section on calibrating the SMPI models from your measurements and fixed some issues
-with the replay mechanism.
+Expected: spring 2022
+
+**On the model checking front**, the long awaited big bang finally occurred, greatly simplifying future evolution.
+
+A formal verification with Mc SimGrid implies two processes: a verified application that is an almost regular SimGrid simulation, and a checker that
+is an external process guiding the verified application to ensure that it explores every possible execution scenario. When formal verification was
+initially introduced in SimGrid 15 years ago, both processes were intertwined in the same system process, but the mandated system tricks made it
+impossible to use gdb or valgrind on that Frankenstein process. Having two heaps in one process is not usually supported.
+
+The design was simplified in v3.12 (2015) by splitting the application and the checker in separate system processes. But both processes remained tightly
+coupled: when the checker needed some information (such as the mailbox implied in a send operation, to compute whether this operation `commutes
+with another one <https://en.wikipedia.org/wiki/Partial_order_reduction>`_), the checker was directly reading the memory of the other system process.
+This was efficient and nice in C, but it prevented us from using C++ features such as opaque ``std::function`` data types. As such, it hindered the
+ongoing SimDAG++ code reorganization toward SimGrid4, where all activity classes should be homogeneously written in modern C++.
+
+This release introduces a new design, where the simcalls are given object-oriented ``Observers`` that can serialize the relevant information over the wire.
+This information is used on the checker side to build ``Transition`` objects that the application simcalls. The checker code is now much simpler, as the
+formal logic is not spoiled with system-level tricks to retrieve the needed information.
+
+This cleaned design allowed us to finally implement the support for mutexes, semaphores and barriers in the model-checker (condition variables are still
+missing). This enables in particular the verification of RMA primitives with Mc SimGrid, as their implementation in SMPI is based on mutexes and barriers.
+Simix, a central element of the SimGrid 3 design, was also finally removed: the last bits are deprecated and will be removed in 3.35. We also replaced the
+old, non-free ISP test suite by the one from the `MPI Bug Initiative <https://hal.archives-ouvertes.fr/hal-03474762>`_ (not all tests are activated yet).
+This will eventually help improving the robustness of Mc SimGrid.
+
+These changes unlock the future of Mc SimGrid. For the next releases, we plan to implement another exploration algorithm based on event unfoldings (using
+`The Anh Pham's thesis <https://tel.archives-ouvertes.fr/tel-02462074/document>`_), the exploration of scenarios where the actors get killed and/or where
+communications timeout, and the addition of a `wrapper to pthreads <https://hal.inria.fr/hal-02449080>`, opening the path to the verification classical
+multithreaded applications.
+
+
+**On the model front,** we continued our quest for the modeling of parallel tasks (ptasks for short). Parallel tasks are intended to be an extension
+of the max-min fairness model (that computes the sharing of communication flows or computation tasks) to tasks mixing resource kinds (e.g., a MPI
+computationnal kernel with computations and communications, or a video stream with IO read, network transfer and decompression on the CPU). Just
+specify the amount of computation for each involved host, the amount of data to transfer between each host pair, and you're set. The model will
+identify bottleneck resources and fairly share them across activities within a ptask. From a user-level perspective, SimGrid handles ptasks just like
+every other activity except that the usual SimGrid models (LV08 or SMPI) rely on an optimized algorithm that cannot handle ptasks. You must
+activate :ref:`the L07 model <s4u_ex_ptasks>` on :ref:`the command line <options_model_select>`. This "model" remains a sort of hack since its introduction 15 years ago, as
+it has never been well defined. We never succeded to unify L07 and max-min based models: Fairness is still to be defined in this context that mixes
+flops and communicated bytes. The resulting activity rates are then specific to ptasks. Furthermore, unlike our network models, this model were not
+thoroughly validated with respect to real experiments before `the thesis of Adrien Faure <https://tel.archives-ouvertes.fr/tel-03155702>`_ (and the
+outcome was quite disappointing). Recent articles by Bonald and Roberts `properly define <https://hal.inria.fr/hal-01243985>`_ the allocation
+objective we had in mind (under the name Bounded MaxMin Fairness -- BMF) and `study the convergence <https://hal.archives-ouvertes.fr/hal-01552739>`_
+of the microscopic dynamic model to a macroscopic equilibrium, but this convergence could only be proved in rather simple cases. Even worse, there is
+no known algorithm to efficiently compute a BMF!
+
+L07 should still be avoided as we have exhibited simple scenarios where its solution is irrelevant to the BMF one (that is mathematically sound). This
+release thus introduces a new BMF model to finally unify both classical and parallel tasks, but this is still ongoing work. The implemented
+heuristic works very well for most SimGrid tests, but we have found some (not so prevalent) corner cases where our code fails to solve the sharing
+problem in over 10 minutes... So this all should still be considered an ongoing research effort. We expect to have a better understanding of this issue
+by the next release.
+
+On a related topic, this release introduces :cpp:func:`simgrid::s4u::this_actor::thread_execute`, which allows creating a computation that comprises
+several threads, and thus capable of utilizing more cores than a classical :cpp:func:`simgrid::s4u::this_actor::execute` action. The goal is to make
+it straightforward to model multithreaded computational kernels, and it comes with an illustrating example. It can be seen as a simplified ptask, but
+since it does not mix bytes and flops and has a homogeneous consumption over a single CPU, it perfectly fits with the classical SimGrid model.
+
+
+.. |br| raw:: html
+
+ <br />
