sc_reduce.h File Reference

Self-contained implementations of MPI_Reduce and MPI_Allreduce. More...

#include <sc.h>

Include dependency graph for sc_reduce.h:

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Macros
#define	SC_REDUCE_ALLTOALL_LEVEL   3
	The highest recursion level that uses direct all-to-all.

Typedefs
typedef void(*	sc_reduce_t) (void *sendbuf, void *recvbuf, int sendcount, sc_MPI_Datatype sendtype)
	Prototype for a user-defined reduce operation.

Functions
int	sc_allreduce_custom (void *sendbuf, void *recvbuf, int sendcount, sc_MPI_Datatype sendtype, sc_reduce_t reduce_fn, sc_MPI_Comm mpicomm)
	Custom allreduce operation with reproducible associativity. More...
int	sc_reduce_custom (void *sendbuf, void *recvbuf, int sendcount, sc_MPI_Datatype sendtype, sc_reduce_t reduce_fn, int target, sc_MPI_Comm mpicomm)
	Custom reduce operation with reproducible associativity. More...
int	sc_allreduce (void *sendbuf, void *recvbuf, int sendcount, sc_MPI_Datatype sendtype, sc_MPI_Op operation, sc_MPI_Comm mpicomm)
	Drop-in MPI_Allreduce replacement with reproducible associativity. More...
int	sc_reduce (void *sendbuf, void *recvbuf, int sendcount, sc_MPI_Datatype sendtype, sc_MPI_Op operation, int target, sc_MPI_Comm mpicomm)
	Drop-in MPI_Reduce replacement with reproducible associativity. More...

Detailed Description

Self-contained implementations of MPI_Reduce and MPI_Allreduce.

Our motivation for writing these alternatives is reproducible associativity. With this implementation, the associativity of the reduction operation depends on the size of the communicator only and does not suffer from random or otherwise obscure influences.

Both algorithms use a binary communication tree. We provide implementations via a customizable reduction operator as well as drop-in replacements for minimum, maximum, and sum. We do not currently support user-defined MPI datatypes.

Function Documentation

sc_allreduce()

int sc_allreduce	(	void *	sendbuf,
		void *	recvbuf,
		int	sendcount,
		sc_MPI_Datatype	sendtype,
		sc_MPI_Op	operation,
		sc_MPI_Comm	mpicomm
	)

Drop-in MPI_Allreduce replacement with reproducible associativity.

Currently we support the operations minimum, maximum, and sum.

Parameters

[in]	sendbuf	Send buffer conforming to MPI specification.
[out]	recvbuf	Receive buffer conforming to MPI specification.
[in]	sendcount	Number of data items to reduce.
[in]	sendtype	Valid MPI datatype.
[in]	operation	sc_MPI_MIN, sc_MPI_MAX, or sc_MPI_SUM. We abort otherwise.
[in]	mpicomm	Valid MPI communicator.

Returns

sc_MPI_SUCCESS if not aborting on MPI error.

sc_allreduce_custom()

int sc_allreduce_custom	(	void *	sendbuf,
		void *	recvbuf,
		int	sendcount,
		sc_MPI_Datatype	sendtype,
		sc_reduce_t	reduce_fn,
		sc_MPI_Comm	mpicomm
	)

Custom allreduce operation with reproducible associativity.

Parameters

[in]	sendbuf	Send buffer conforming to MPI specification.
[out]	recvbuf	Receive buffer conforming to MPI specification.
[in]	sendcount	Number of data items to reduce.
[in]	sendtype	Valid MPI datatype.
[in]	reduce_fn	Custom, associative reduction operator.
[in]	mpicomm	Valid MPI communicator.

Returns

sc_MPI_SUCCESS if not aborting on MPI error.

sc_reduce()

int sc_reduce	(	void *	sendbuf,
		void *	recvbuf,
		int	sendcount,
		sc_MPI_Datatype	sendtype,
		sc_MPI_Op	operation,
		int	target,
		sc_MPI_Comm	mpicomm
	)

Drop-in MPI_Reduce replacement with reproducible associativity.

Currently we support the operations minimum, maximum, and sum.

Parameters

[in]	sendbuf	Send buffer conforming to MPI specification.
[out]	recvbuf	Receive buffer conforming to MPI specification.
[in]	sendcount	Number of data items to reduce.
[in]	sendtype	Valid MPI datatype.
[in]	operation	sc_MPI_MIN, sc_MPI_MAX, or sc_MPI_SUM. We abort otherwise.
[in]	target	The MPI rank that obtains the result.
[in]	mpicomm	Valid MPI communicator.

Returns

sc_MPI_SUCCESS if not aborting on MPI error.

sc_reduce_custom()

int sc_reduce_custom	(	void *	sendbuf,
		void *	recvbuf,
		int	sendcount,
		sc_MPI_Datatype	sendtype,
		sc_reduce_t	reduce_fn,
		int	target,
		sc_MPI_Comm	mpicomm
	)

Custom reduce operation with reproducible associativity.

Parameters

[in]	sendbuf	Send buffer conforming to MPI specification.
[out]	recvbuf	Receive buffer conforming to MPI specification.
[in]	sendcount	Number of data items to reduce.
[in]	sendtype	Valid MPI datatype.
[in]	reduce_fn	Custom, associative reduction operator.
[in]	target	The MPI rank that obtains the result.
[in]	mpicomm	Valid MPI communicator.

Returns

sc_MPI_SUCCESS if not aborting on MPI error.