gmx::MpiComm Class Reference

#include <gromacs/utility/mpicomm.h>

Description

MPI communicator with optimized reduction functionality.

This class refers to an MPI communicator and derived data and provides summation reductions that can be hierarchical.

Note

The lifetime of the communicator should be managed externally.

Classes
struct	SingleRank
	Helper type to differentiate single-rank constructor. More...

Public Member Functions
	MpiComm (MPI_Comm comm)
	Constructs an object for MPI communicator comm.
	MpiComm (SingleRank)
	Constructs a communicator with a single rank. More...
	MpiComm (const MpiComm &other)
	Copy constructor.
	MpiComm (MpiComm &&other)=delete
	Move constructor.
	~MpiComm ()
	Destructor.
MpiComm &	operator= (const MpiComm &other)
	Copy assignment.
MpiComm &	operator= (MpiComm &&other) noexcept
	Move assignment.
MPI_Comm	comm () const
int	size () const
	Returns the number of ranks in the communicator.
bool	isSerial () const
	Returns true when size() == 1.
bool	isParallel () const
	Returns true when size() > 1.
int	rank () const
	Returns our rank id in the communicator.
bool	isMainRank () const
	Returns whether our rank is the main rank.
int	mainRank () const
	Returns the rank id of the main rank.
void	initializeHierarchicalReductions (int physicalNodeIdHash)
	Initializes hierarchical reductions. More...
std::optional< std::string >	getHierarchicalReductionsReport () const
	Returns a string describing the hierarchical reduction, when it is active.
void	sumReduce (ArrayRef< int > data) const
	Reduce ints over all ranks, results on all ranks, can use hierarchical reduction.
void	sumReduce (ArrayRef< float > data) const
	Reduce floats over all ranks, results on all ranks, can use hierarchical reduction.
void	sumReduce (ArrayRef< double > data) const
	Reduce doubles over all ranks, results on all ranks, can use hierarchical reduction.
void	sumReduce (std::size_t nr, int *data) const
	Reduce ints over all ranks, results on all ranks, can use hierarchical reduction.
void	sumReduce (std::size_t nr, float *data) const
	Reduce floats over all ranks, results on all ranks, can use hierarchical reduction.
void	sumReduce (std::size_t nr, double *data) const
	Reduce doubles over all ranks, results on all ranks, can use hierarchical reduction.
std::vector< std::string >	collectStrings (std::string_view myString) const
	Collect strings from all ranks onto the main.

Constructor & Destructor Documentation

gmx::MpiComm::MpiComm

(

SingleRank

)

Constructs a communicator with a single rank.

Note

The comm() method will return MPI_COMM_NULL. This communicator should not be passed to MPI calls. Thus any code that might take an MpiComm object constructed by this constructor should check for size() > 1 before calling MPI calls. Note that the sumReduce() methods of this class are safe to call.

Member Function Documentation

void gmx::MpiComm::initializeHierarchicalReductions

(

int

physicalNodeIdHash

)

Initializes hierarchical reductions.

When running on system with many nodes, it can be faster to reduce within nodes first and the reduce over nodes using one rank per node. This method initializes such hierarchical reductions. The request is only granted when there is actually such a hierarchy and then is a sufficient number of ranks involved. When that is the case, all later calls to sumReduce() will use hierarchical redution. When not, a single reduction will be used.

Parameters

physicalNodeIdHash

An integer that should be unique for each physical node

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The documentation for this class was generated from the following files:

• src/gromacs/utility/mpicomm.h
• src/gromacs/utility/mpicomm.cpp