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shmem_comp4_sum_to_all(3), shmem_comp8_sum_to_all(3), shmem_complexd_sum_to_all(3),
shmem_complexf_sum_to_all(3), shmem_double_sum_to_all(3), shmem_float_sum_to_all(3),
shmem_int_sum_to_all(3), shmem_int4_sum_to_all(3), shmem_int8_sum_to_all(3),
shmem_long_sum_to_all(3), shmem_longdouble_sum_to_all(3), shmem_longlong_sum_to_all(3),
shmem_real4_sum_to_all(3), shmem_real8_sum_to_all(3), shmem_real16_sum_to_all(3),
shmem_short_sum_to_all(3)  Performs a sum reduction across a set of processing
elements (PEs)
C or C++:
#include <mpp/shmem.h>
void shmem_complexd_sum_to_all(double complex *target,
const double complex *source, int nreduce, int PE_start,
int logPE_stride, int PE_size, double complex *pWrk,
long *pSync);
void shmem_complexf_sum_to_all(float complex *target,
const float complex *source, int nreduce, int PE_start,
int logPE_stride, int PE_size, float complex *pWrk,
long *pSync);
void shmem_double_sum_to_all(double *target,
const double *source, int nreduce, int PE_start, int logPE_stride,
int PE_size, double *pWrk, long *pSync);
void shmem_float_sum_to_all(float *target, const float *source,
int nreduce, int PE_start, int logPE_stride, int PE_size,
float *pWrk, long *pSync);
void shmem_int_sum_to_all(int *target, const int *source,
int nreduce, int PE_start, int logPE_stride, int PE_size,
int *pWrk, long *pSync);
void shmem_long_sum_to_all(long *target, const long *source,
int nreduce, int PE_start, int logPE_stride, int PE_size,
long *pWrk, long *pSync);
void shmem_longdouble_sum_to_all(long double *target,
const long double *source, int nreduce, int PE_start, int
logPE_stride, int PE_size, long double *pWrk, long *pSync);
void shmem_longlong_sum_to_all(long long *target,
const long long *source, int nreduce, int PE_start,
int logPE_stride, int PE_size, long long *pWrk,
long *pSync);
void shmem_short_sum_to_all(short *target, const short *source,
int nreduce, int PE_start, int logPE_stride, int PE_size,
short *pWrk, long *pSync);
Fortran:
INCLUDE "mpp/shmem.fh"
INTEGER pSync(SHMEM_REDUCE_SYNC_SIZE)
INTEGER nreduce, PE_start, logPE_stride, PE_size
CALL SHMEM_COMP4_SUM_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
CALL SHMEM_COMP8_SUM_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
CALL SHMEM_INT4_SUM_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
CALL SHMEM_INT8_SUM_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
CALL SHMEM_REAL4_SUM_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
CALL SHMEM_REAL8_SUM_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
CALL SHMEM_REAL16_SUM_TO_ALL(target, source, nreduce,
& PE_start, logPE_stride, PE_size, pWrk, pSync)
The shared memory (SHMEM) reduction routines compute one or
more reductions across symmetric arrays on multiple virtual PEs. A reduction
performs an associative binary operation across a set of values. For a list
of other SHMEM reduction routines, see intro_shmem(3).
As with all SHMEM
collective routines, each of these routines assumes that only PEs in the
active set call the routine. If a PE not in the active set calls a SHMEM
collective routine, undefined behavior results.
The nreduce argument determines
the number of separate reductions to perform. The source array on all PEs
in the active set provides one element for each reduction. The results of
the reductions are placed in the target array on all PEs in the active
set. The active set is defined by the PE_start, logPE_stride, PE_size triplet.
The source and target arrays may be the same array, but they may not be
overlapping arrays.
The arguments are as follows:
 target
 The remotely accessible
integer data object to be updated on the remote PE. If you are using C/C++,
the type of target should match that implied in the SYNOPSIS section. If
you are using the Fortran compiler, it must be of type integer with an
element size of 4 bytes for SHMEM_INT4_ADD and 8 bytes for SHMEM_INT8_ADD.
 value
 The value to be atomically added to target. If you are using C/C++,
the type of value should match that implied in the SYNOPSIS section. If
you are using Fortran, it must be of type integer with an element size
of target.
 pe
 An integer that indicates the PE number upon which target
is to be updated. If you are using Fortran, it must be a default integer
value.
 target
 A symmetric array of length nreduce elements to receive the
results of the reduction operations.
The data type of target varies with the version of the reduction routine
being called and the language used. When calling from C/C++, refer to the
SYNOPSIS section for data type information. When calling from Fortran, the
target data types are as follows:
 shmem_comp4_sum_to_all: COMPLEX(KIND=4).
 shmem_comp8_sum_to_all: Complex. If you are using Fortran, it must be
 a
default complex value.
 shmem_int4_sum_to_all: INTEGER(KIND=4).
 shmem_int8_sum_to_all:
Integer. If you are using Fortran, it must be a
 default integer value.
 shmem_real4_sum_to_all:
REAL(KIND=4).
 shmem_real8_sum_to_all: Real. If you are using Fortran, it
must be a
 default real value.
 shmem_real16_sum_to_all: Real. If you are using
Fortran, it must be a
 default real value.
 source
 A symmetric array, of length
nreduce elements, that contains one element for each separate reduction
operation. The source argument must have the same data type as target.
 nreduce
 The number of elements in the target and source arrays. nreduce must be
of type integer. If you are using Fortran, it must be a default integer
value.
 PE_start
 The lowest virtual PE number of the active set of PEs. PE_start
must be of type integer. If you are using Fortran, it must be a default
integer value.
 logPE_stride
 The log (base 2) of the stride between consecutive
virtual PE numbers in the active set. logPE_stride must be of type integer.
If you are using Fortran, it must be a default integer value.
 PE_size
 The
number of PEs in the active set. PE_size must be of type integer. If you
are using Fortran, it must be a default integer value.
 pWrk
 A symmetric
work array. The pWrk argument must have the same data type as target. In
C/C++, this contains max(nreduce/2 + 1, _SHMEM_REDUCE_MIN_WRKDATA_SIZE)
elements. In Fortran, this contains max(nreduce/2 + 1, SHMEM_REDUCE_MIN_WRKDATA_SIZE)
elements.
 pSync
 A symmetric work array. In C/C++, pSync is of type long and
size _SHMEM_REDUCE_SYNC_SIZE. In Fortran, pSync is of type integer and size
SHMEM_REDUCE_SYNC_SIZE. It must be a default integer value. Every element
of this array must be initialized with the value _SHMEM_SYNC_VALUE (in
C/C++) or SHMEM_SYNC_VALUE (in Fortran) before any of the PEs in the active
set enter the reduction routine.
The values of arguments nreduce, PE_start,
logPE_stride, and PE_size must be equal on all PEs in the active set. The
same target and source arrays, and the same pWrk and pSync work arrays,
must be passed to all PEs in the active set.
Before any PE calls a reduction
routine, you must ensure that the following conditions exist (synchronization
via a barrier or some other method is often needed to ensure this): The
pWrk and pSync arrays on all PEs in the active set are not still in use
from a prior call to a collective SHMEM routine. The target array on all
PEs in the active set is ready to accept the results of the reduction.
Upon
return from a reduction routine, the following are true for the local PE:
The target array is updated. The values in the pSync array are restored
to the original values.
The terms collective, symmetric, and cache
aligned are defined in intro_shmem(3).
All SHMEM reduction routines reset
the values in pSync before they return, so a particular pSync buffer need
only be initialized the first time it is used.
You must ensure that the
pSync array is not being updated on any PE in the active set while any
of the PEs participate in processing of a SHMEM reduction routine. Be careful
of the following situations: If the pSync array is initialized at run time,
some type of synchronization is needed to ensure that all PEs in the working
set have initialized pSync before any of them enter a SHMEM routine called
with the pSync synchronization array. A pSync or pWrk array can be reused
in a subsequent reduction routine call only if none of the PEs in the active
set are still processing a prior reduction routine call that used the same
pSync or pWrk arrays. In general, this can be assured only by doing some
type of synchronization. However, in the special case of reduction routines
being called with the same active set, you can allocate two pSync and pWrk
arrays and alternate between them on successive calls.
Example
1: This Fortran example statically initializes the pSync array and finds
the sum of the real variable FOO across all even PEs.
INCLUDE "mpp/shmem.fh"
INTEGER PSYNC(SHMEM_REDUCE_SYNC_SIZE)
DATA PSYNC /SHMEM_REDUCE_SYNC_SIZE*SHMEM_SYNC_VALUE/
PARAMETER (NR=1)
REAL FOO, FOOSUM, PWRK(MAX(NR/2+1,SHMEM_REDUCE_MIN_WRKDATA_SIZE))
COMMON /COM/ FOO, FOOSUM, PWRK
INTRINSIC MY_PE
IF ( MOD(MY_PE(),2) .EQ. 0) THEN
CALL SHMEM_INT4_SUM_TO_ALL(FOOSUM, FOO, NR, 0, 1, N$PES/2,
& PWRK, PSYNC)
PRINT *, ’Result on PE ’, MY_PE(), ’ is ’, FOOSUM
ENDIF
Example 2: Consider the following C/C++ call:
shmem_int_sum_to_all( target, source, 3, 0, 0, 8, pwrk, psync );
The preceding call is more efficient, but semantically equivalent to,
the combination of the following calls:
shmem_int_sum_to_all(&(target[0]), &(source[0]), 1, 0, 0, 8,
pwrk1, psync1);
shmem_int_sum_to_all(&(target[1]), &(source[1]), 1, 0, 0, 8,
pwrk2, psync2);
shmem_int_sum_to_all(&(target[2]), &(source[2]), 1, 0, 0, 8,
pwrk1, psync1);
Note that two sets of pWrk and pSync arrays are used alternately because
no
synchronization is done between calls.
intro_shmem(3)
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