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Library to introduce fault-tolerance in MPI in the form of graceful degradation

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Library to introduce fault-tolerance in MPI in the form of graceful degradation

We are led on by courage, and obedience, and fortitude, which [...] does not desert us in our ill fortune.

-- Titus Flavius Josephus

Overview

Legio is a library that introduces fault-tolerance in MPI applications in the form of graceful degradation. It's designed for embarrassingly parallel applications. It is based on ULFM.

Usage

One of the key aspects of Legio is the transparency of integration: no changes in the code are needed, integration is performed via linking. Legio leverages PMPI to catch all the calls toward MPI and wraps them with the appropriate code needed. If you have ULFM already installed, run:

$ export ULFM_PREFIX <path-to-ulfm-install-folder>

To install the Legio library, follow the standard CMake installation procedure:

$ mkdir build
$ cd build
$ cmake -DCMAKE_INSTALL_PREFIX=<installation_prefix> ..
$ make
$ make install

MPI functions supported

The list of the functions supported can be found in this file, together with an analysis on the difficulty of integration for the non-supported ones and a brief note on what should be done.

Support for other calls is under development.

Configuration

It is possible to configure the behaviour of the Legio library at configuration time, changing some CMake variables. The following table shows all the possible configurations knobs with their meanings.

Variable Values Default Meaning
WITH_TESTS On/Off On Build example programs from legiotest directory
WITH_SESSION_TESTS On/Off Off Build sessions unit tests
WITH_EXAMPLES On/Off Off Build example ULFM programs from testsrc directory
BROADCAST_RESILIENCY On/Off Off Specify if the execution can continue whenever the root of a broadcast operation fails
SEND_RESILIENCY On/Off On Specify if the execution can continue whenever the destination of a send operation fails
NUM_RETRY any strictly positive integer 3 Number of retries for a failed send operation
RECV_RESILIENCY On/Off Off Specify if the execution can continue whenever the source of a recv operation fails
REDUCE_RESILIENCY On/Off On Specify if the execution can continue whenever the root of a reduce operation fails
GET_RESILIENCY On/Off Off Specify if the execution can continue whenever the source of a get operation fails
PUT_RESILIENCY On/Off On Specify if the execution can continue whenever the destination of a put operation fails
GATHER_RESILIENCY On/Off On Specify if the execution can continue whenever the root of a gather operation fails
GATHER_SHIFT On/Off Off Specify if failures impact the way data is distributed among the processes
SCATTER_RESILIENCY On/Off Off Specify if the execution can continue whenever the root of a scatter operation fails
SCATTER_SHIFT On/Off Off Specify if failures impact the way data is collected from the processes
LOG_LEVEL 1-4 2 Specify the log level (1->None, 2->Errors, 3->Errors&info, 4->Full)
SESSION_THREAD On/Off Off Use a separate thread to handle the horizon communicator initialisation
WITH_RESTART On/Off On Include critical nodes restart functionalities
WITH_SESSION On/Off On Include MPI_Session support (set to Off on MPI versions prior to 4.0)
CUBE_ALGORITHM On/Off Off Use the Hypercube LDA instead of the Tree-based one

To change the default configuration of the Legio library, add options to the cmake command in the form -D[Variable]=[Value].

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