allreduce.c 33 KB
Newer Older
1
/* -*- Mode: C; c-basic-offset:4 ; -*- */
2
/*
3
4
5
6
7
 *  (C) 2001 by Argonne National Laboratory.
 *      See COPYRIGHT in top-level directory.
 */

#include "mpiimpl.h"
8
#include "collutil.h"
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

/* -- Begin Profiling Symbol Block for routine MPI_Allreduce */
#if defined(HAVE_PRAGMA_WEAK)
#pragma weak MPI_Allreduce = PMPI_Allreduce
#elif defined(HAVE_PRAGMA_HP_SEC_DEF)
#pragma _HP_SECONDARY_DEF PMPI_Allreduce  MPI_Allreduce
#elif defined(HAVE_PRAGMA_CRI_DUP)
#pragma _CRI duplicate MPI_Allreduce as PMPI_Allreduce
#endif
/* -- End Profiling Symbol Block */

/* Define MPICH_MPI_FROM_PMPI if weak symbols are not supported to build
   the MPI routines */
#ifndef MPICH_MPI_FROM_PMPI
#undef MPI_Allreduce
#define MPI_Allreduce PMPI_Allreduce

26
27
/* The order of entries in this table must match the definitions in 
   mpi.h.in */
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
MPI_User_function *MPIR_Op_table[] = { MPIR_MAXF, MPIR_MINF, MPIR_SUM,
                                       MPIR_PROD, MPIR_LAND,
                                       MPIR_BAND, MPIR_LOR, MPIR_BOR,
                                       MPIR_LXOR, MPIR_BXOR,
                                       MPIR_MINLOC, MPIR_MAXLOC, };

MPIR_Op_check_dtype_fn *MPIR_Op_check_dtype_table[] = {
    MPIR_MAXF_check_dtype, MPIR_MINF_check_dtype,
    MPIR_SUM_check_dtype,
    MPIR_PROD_check_dtype, MPIR_LAND_check_dtype,
    MPIR_BAND_check_dtype, MPIR_LOR_check_dtype, MPIR_BOR_check_dtype,
    MPIR_LXOR_check_dtype, MPIR_BXOR_check_dtype,
    MPIR_MINLOC_check_dtype, MPIR_MAXLOC_check_dtype, }; 


/* This is the default implementation of allreduce. The algorithm is:
   
   Algorithm: MPI_Allreduce

   For the heterogeneous case, we call MPI_Reduce followed by MPI_Bcast
   in order to meet the requirement that all processes must have the
   same result. For the homogeneous case, we use the following algorithms.


   For long messages and for builtin ops and if count >= pof2 (where
   pof2 is the nearest power-of-two less than or equal to the number
   of processes), we use Rabenseifner's algorithm (see 
55
   http://www.hlrs.de/mpi/myreduce.html).
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
   This algorithm implements the allreduce in two steps: first a
   reduce-scatter, followed by an allgather. A recursive-halving
   algorithm (beginning with processes that are distance 1 apart) is
   used for the reduce-scatter, and a recursive doubling 
   algorithm is used for the allgather. The non-power-of-two case is
   handled by dropping to the nearest lower power-of-two: the first
   few even-numbered processes send their data to their right neighbors
   (rank+1), and the reduce-scatter and allgather happen among the remaining
   power-of-two processes. At the end, the first few even-numbered
   processes get the result from their right neighbors.

   For the power-of-two case, the cost for the reduce-scatter is 
   lgp.alpha + n.((p-1)/p).beta + n.((p-1)/p).gamma. The cost for the
   allgather lgp.alpha + n.((p-1)/p).beta. Therefore, the
   total cost is:
   Cost = 2.lgp.alpha + 2.n.((p-1)/p).beta + n.((p-1)/p).gamma

   For the non-power-of-two case, 
   Cost = (2.floor(lgp)+2).alpha + (2.((p-1)/p) + 2).n.beta + n.(1+(p-1)/p).gamma

   
77
78
79
80
81
82
83
   For short messages, for user-defined ops, and for count < pof2 
   we use a recursive doubling algorithm (similar to the one in
   MPI_Allgather). We use this algorithm in the case of user-defined ops
   because in this case derived datatypes are allowed, and the user
   could pass basic datatypes on one process and derived on another as
   long as the type maps are the same. Breaking up derived datatypes
   to do the reduce-scatter is tricky. 
84
85
86
87
88
89
90
91

   Cost = lgp.alpha + n.lgp.beta + n.lgp.gamma

   Possible improvements: 

   End Algorithm: MPI_Allreduce
*/

92
93
94
95
96
#undef FUNCNAME
#define FUNCNAME allreduce_intra_or_coll_fn
#undef FCNAME
#define FCNAME MPIU_QUOTE(FUNCNAME)
static inline int allreduce_intra_or_coll_fn(void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype, MPI_Op op,
97
                                             MPID_Comm *comm_ptr, int *errflag)
98
99
100
101
{
    int mpi_errno = MPI_SUCCESS;

    if (comm_ptr->coll_fns != NULL && comm_ptr->coll_fns->Allreduce != NULL) {
102
	/* --BEGIN USEREXTENSION-- */
103
	mpi_errno = comm_ptr->coll_fns->Allreduce(sendbuf, recvbuf, count, datatype, op, comm_ptr, errflag);
104
        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
105
	/* --END USEREXTENSION-- */
106
    } else {
107
        mpi_errno = MPIR_Allreduce_intra(sendbuf, recvbuf, count, datatype, op, comm_ptr, errflag);
108
109
110
111
112
113
114
115
116
        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
    }
        
 fn_exit:
    return mpi_errno;
 fn_fail:
    goto fn_exit;
}

117
118
119

/* not declared static because a machine-specific function may call this one 
   in some cases */
120
121
122
123
124
#undef FUNCNAME
#define FUNCNAME MPIR_Allreduce_intra
#undef FCNAME
#define FCNAME MPIU_QUOTE(FUNCNAME)
int MPIR_Allreduce_intra ( 
125
    const void *sendbuf,
126
127
128
129
    void *recvbuf, 
    int count, 
    MPI_Datatype datatype, 
    MPI_Op op, 
130
131
    MPID_Comm *comm_ptr,
    int *errflag )
132
133
{
#ifdef MPID_HAS_HETERO
Pavan Balaji's avatar
Pavan Balaji committed
134
    int is_homogeneous;
135
136
137
    int rc;
#endif
    int        comm_size, rank, type_size;
138
139
    int mpi_errno = MPI_SUCCESS;
    int mpi_errno_ret = MPI_SUCCESS;
140
141
142
143
144
145
146
    int mask, dst, is_commutative, pof2, newrank, rem, newdst, i,
        send_idx, recv_idx, last_idx, send_cnt, recv_cnt, *cnts, *disps; 
    MPI_Aint true_extent, true_lb, extent;
    void *tmp_buf;
    MPI_Comm comm;
    MPIU_CHKLMEM_DECL(3);
    
147
148
149
150
    /* check if multiple threads are calling this collective function */
    MPIDU_ERR_CHECK_MULTIPLE_THREADS_ENTER( comm_ptr );

    if (count == 0) goto fn_exit;
151
152
    comm = comm_ptr->handle;

153
    is_commutative = MPIR_Op_is_commutative(op);
154
155

#if defined(USE_SMP_COLLECTIVES)
156
    /* is the op commutative? We do SMP optimizations only if it is. */
157
158
    if (MPIR_Comm_is_node_aware(comm_ptr) && is_commutative) {
        /* on each node, do a reduce to the local root */ 
159
        if (comm_ptr->node_comm != NULL) {
160
161
162
163
164
165
166
167
            /* take care of the MPI_IN_PLACE case. For reduce, 
               MPI_IN_PLACE is specified only on the root; 
               for allreduce it is specified on all processes. */

            if ((sendbuf == MPI_IN_PLACE) && (comm_ptr->node_comm->rank != 0)) {
                /* IN_PLACE and not root of reduce. Data supplied to this
                   allreduce is in recvbuf. Pass that as the sendbuf to reduce. */
			
168
                mpi_errno = MPIR_Reduce_impl(recvbuf, NULL, count, datatype, op, 0, comm_ptr->node_comm, errflag);
169
170
                if (mpi_errno) {
                    /* for communication errors, just record the error but continue */
171
                    *errflag = TRUE;
172
173
174
                    MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                    MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
                }
175
            } else {
176
                mpi_errno = MPIR_Reduce_impl(sendbuf, recvbuf, count, datatype, op, 0, comm_ptr->node_comm, errflag);
177
178
                if (mpi_errno) {
                    /* for communication errors, just record the error but continue */
179
                    *errflag = TRUE;
180
181
182
                    MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                    MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
                }
183
            }
184
        } else {
185
186
187
            /* only one process on the node. copy sendbuf to recvbuf */
            if (sendbuf != MPI_IN_PLACE) {
                mpi_errno = MPIR_Localcopy(sendbuf, count, datatype, recvbuf, count, datatype);
188
                if (mpi_errno) MPIU_ERR_POP(mpi_errno);
189
190
191
192
193
            }
        }

        /* now do an IN_PLACE allreduce among the local roots of all nodes */
        if (comm_ptr->node_roots_comm != NULL) {
194
195
            mpi_errno = allreduce_intra_or_coll_fn(MPI_IN_PLACE, recvbuf, count, datatype, op, comm_ptr->node_roots_comm,
                                                   errflag);
196
197
            if (mpi_errno) {
                /* for communication errors, just record the error but continue */
198
                *errflag = TRUE;
199
200
201
                MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
            }
202
203
204
205
        }

        /* now broadcast the result among local processes */
        if (comm_ptr->node_comm != NULL) {
206
            mpi_errno = MPIR_Bcast_impl(recvbuf, count, datatype, 0, comm_ptr->node_comm, errflag);
207
208
            if (mpi_errno) {
                /* for communication errors, just record the error but continue */
209
                *errflag = TRUE;
210
211
212
                MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
            }
213
214
215
216
217
        }
        goto fn_exit;
    }
#endif
            
218
219
220
221
    
#ifdef MPID_HAS_HETERO
    if (comm_ptr->is_hetero)
        is_homogeneous = 0;
Pavan Balaji's avatar
Pavan Balaji committed
222
223
    else
        is_homogeneous = 1;
224
225
226
227
228
229
#endif
    
#ifdef MPID_HAS_HETERO
    if (!is_homogeneous) {
        /* heterogeneous. To get the same result on all processes, we
           do a reduce to 0 and then broadcast. */
230
        mpi_errno = MPIR_Reduce_impl ( sendbuf, recvbuf, count, datatype,
231
                                       op, 0, comm_ptr, errflag );
232
233
        if (mpi_errno) {
            /* for communication errors, just record the error but continue */
234
            *errflag = TRUE;
235
236
237
238
            MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
            MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
        }

239
        mpi_errno = MPIR_Bcast_impl( recvbuf, count, datatype, 0, comm_ptr, errflag );
240
241
        if (mpi_errno) {
            /* for communication errors, just record the error but continue */
242
            *errflag = TRUE;
243
244
            MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
            MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
245
246
247
248
249
250
251
252
253
        }
    }
    else 
#endif /* MPID_HAS_HETERO */
    {
        /* homogeneous */

        comm_size = comm_ptr->local_size;
        rank = comm_ptr->rank;
254
255
256

        is_commutative = MPIR_Op_is_commutative(op);

257
        /* need to allocate temporary buffer to store incoming data*/
258
        MPIR_Type_get_true_extent_impl(datatype, &true_lb, &true_extent);
259
260
        MPID_Datatype_get_extent_macro(datatype, extent);

261
        MPID_Ensure_Aint_fits_in_pointer(count * MPIR_MAX(extent, true_extent));
262
263
264
265
266
267
268
269
270
        MPIU_CHKLMEM_MALLOC(tmp_buf, void *, count*(MPIR_MAX(extent,true_extent)), mpi_errno, "temporary buffer");
	
        /* adjust for potential negative lower bound in datatype */
        tmp_buf = (void *)((char*)tmp_buf - true_lb);
        
        /* copy local data into recvbuf */
        if (sendbuf != MPI_IN_PLACE) {
            mpi_errno = MPIR_Localcopy(sendbuf, count, datatype, recvbuf,
                                       count, datatype);
271
            if (mpi_errno) MPIU_ERR_POP(mpi_errno);
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
        }

        MPID_Datatype_get_size_macro(datatype, type_size);

        /* find nearest power-of-two less than or equal to comm_size */
        pof2 = 1;
        while (pof2 <= comm_size) pof2 <<= 1;
        pof2 >>=1;

        rem = comm_size - pof2;

        /* In the non-power-of-two case, all even-numbered
           processes of rank < 2*rem send their data to
           (rank+1). These even-numbered processes no longer
           participate in the algorithm until the very end. The
           remaining processes form a nice power-of-two. */
        
        if (rank < 2*rem) {
            if (rank % 2 == 0) { /* even */
291
292
293
                mpi_errno = MPIC_Send_ft(recvbuf, count, 
                                         datatype, rank+1,
                                         MPIR_ALLREDUCE_TAG, comm, errflag);
294
295
                if (mpi_errno) {
                    /* for communication errors, just record the error but continue */
296
                    *errflag = TRUE;
297
298
299
                    MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                    MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
                }
300
301
302
303
304
305
306
                
                /* temporarily set the rank to -1 so that this
                   process does not pariticipate in recursive
                   doubling */
                newrank = -1; 
            }
            else { /* odd */
307
308
309
310
                mpi_errno = MPIC_Recv_ft(tmp_buf, count, 
                                         datatype, rank-1,
                                         MPIR_ALLREDUCE_TAG, comm,
                                         MPI_STATUS_IGNORE, errflag);
311
312
                if (mpi_errno) {
                    /* for communication errors, just record the error but continue */
313
                    *errflag = TRUE;
314
315
316
                    MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                    MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
                }
317

318
319
320
                /* do the reduction on received data. since the
                   ordering is right, it doesn't matter whether
                   the operation is commutative or not. */
321
322
323
                mpi_errno = MPIR_Reduce_local_impl(tmp_buf, recvbuf, count, datatype, op);
                if (mpi_errno) MPIU_ERR_POP(mpi_errno);

324
325
326
327
328
329
330
                /* change the rank */
                newrank = rank / 2;
            }
        }
        else  /* rank >= 2*rem */
            newrank = rank - rem;
        
331
332
333
334
335
336
337
338
339
        /* If op is user-defined or count is less than pof2, use
           recursive doubling algorithm. Otherwise do a reduce-scatter
           followed by allgather. (If op is user-defined,
           derived datatypes are allowed and the user could pass basic
           datatypes on one process and derived on another as long as
           the type maps are the same. Breaking up derived
           datatypes to do the reduce-scatter is tricky, therefore
           using recursive doubling in that case.) */

340
        if (newrank != -1) {
341
            if ((count*type_size <= MPIR_PARAM_ALLREDUCE_SHORT_MSG_SIZE) ||
342
                (HANDLE_GET_KIND(op) != HANDLE_KIND_BUILTIN) ||  
343
344
345
346
347
348
349
350
351
                (count < pof2)) { /* use recursive doubling */
                mask = 0x1;
                while (mask < pof2) {
                    newdst = newrank ^ mask;
                    /* find real rank of dest */
                    dst = (newdst < rem) ? newdst*2 + 1 : newdst + rem;

                    /* Send the most current data, which is in recvbuf. Recv
                       into tmp_buf */ 
352
353
354
355
356
                    mpi_errno = MPIC_Sendrecv_ft(recvbuf, count, datatype, 
                                                 dst, MPIR_ALLREDUCE_TAG, tmp_buf,
                                                 count, datatype, dst,
                                                 MPIR_ALLREDUCE_TAG, comm,
                                                 MPI_STATUS_IGNORE, errflag);
357
358
                    if (mpi_errno) {
                        /* for communication errors, just record the error but continue */
359
                        *errflag = TRUE;
360
361
362
                        MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                        MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
                    }
363
364
365
366
367
368
                    
                    /* tmp_buf contains data received in this step.
                       recvbuf contains data accumulated so far */
                    
                    if (is_commutative  || (dst < rank)) {
                        /* op is commutative OR the order is already right */
369
370
                        mpi_errno = MPIR_Reduce_local_impl(tmp_buf, recvbuf, count, datatype, op);
                        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
371
372
373
                    }
                    else {
                        /* op is noncommutative and the order is not right */
374
375
376
                        mpi_errno = MPIR_Reduce_local_impl(recvbuf, tmp_buf, count, datatype, op);
                        if (mpi_errno) MPIU_ERR_POP(mpi_errno);

377
378
379
                        /* copy result back into recvbuf */
                        mpi_errno = MPIR_Localcopy(tmp_buf, count, datatype,
                                                   recvbuf, count, datatype);
380
                        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
                    }
                    mask <<= 1;
                }
            }

            else {

                /* do a reduce-scatter followed by allgather */

                /* for the reduce-scatter, calculate the count that
                   each process receives and the displacement within
                   the buffer */

		MPIU_CHKLMEM_MALLOC(cnts, int *, pof2*sizeof(int), mpi_errno, "counts");
		MPIU_CHKLMEM_MALLOC(disps, int *, pof2*sizeof(int), mpi_errno, "displacements");

                for (i=0; i<(pof2-1); i++) 
                    cnts[i] = count/pof2;
                cnts[pof2-1] = count - (count/pof2)*(pof2-1);

                disps[0] = 0;
                for (i=1; i<pof2; i++)
                    disps[i] = disps[i-1] + cnts[i-1];

                mask = 0x1;
                send_idx = recv_idx = 0;
                last_idx = pof2;
                while (mask < pof2) {
                    newdst = newrank ^ mask;
                    /* find real rank of dest */
                    dst = (newdst < rem) ? newdst*2 + 1 : newdst + rem;

                    send_cnt = recv_cnt = 0;
                    if (newrank < newdst) {
                        send_idx = recv_idx + pof2/(mask*2);
                        for (i=send_idx; i<last_idx; i++)
                            send_cnt += cnts[i];
                        for (i=recv_idx; i<send_idx; i++)
                            recv_cnt += cnts[i];
                    }
                    else {
                        recv_idx = send_idx + pof2/(mask*2);
                        for (i=send_idx; i<recv_idx; i++)
                            send_cnt += cnts[i];
                        for (i=recv_idx; i<last_idx; i++)
                            recv_cnt += cnts[i];
                    }

/*                    printf("Rank %d, send_idx %d, recv_idx %d, send_cnt %d, recv_cnt %d, last_idx %d\n", newrank, send_idx, recv_idx,
                           send_cnt, recv_cnt, last_idx);
                           */
                    /* Send data from recvbuf. Recv into tmp_buf */ 
433
434
435
436
437
438
439
440
441
                    mpi_errno = MPIC_Sendrecv_ft((char *) recvbuf +
                                                 disps[send_idx]*extent,
                                                 send_cnt, datatype,  
                                                 dst, MPIR_ALLREDUCE_TAG, 
                                                 (char *) tmp_buf +
                                                 disps[recv_idx]*extent,
                                                 recv_cnt, datatype, dst,
                                                 MPIR_ALLREDUCE_TAG, comm,
                                                 MPI_STATUS_IGNORE, errflag);
442
443
                    if (mpi_errno) {
                        /* for communication errors, just record the error but continue */
444
                        *errflag = TRUE;
445
446
447
                        MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                        MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
                    }
448
449
450
451
452
453
                    
                    /* tmp_buf contains data received in this step.
                       recvbuf contains data accumulated so far */
                    
                    /* This algorithm is used only for predefined ops
                       and predefined ops are always commutative. */
454
455
456
457
                    mpi_errno = MPIR_Reduce_local_impl(((char *) tmp_buf + disps[recv_idx]*extent),
                                                       ((char *) recvbuf + disps[recv_idx]*extent),
                                                       recv_cnt, datatype, op);
                    if (mpi_errno) MPIU_ERR_POP(mpi_errno);
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497

                    /* update send_idx for next iteration */
                    send_idx = recv_idx;
                    mask <<= 1;

                    /* update last_idx, but not in last iteration
                       because the value is needed in the allgather
                       step below. */
                    if (mask < pof2)
                        last_idx = recv_idx + pof2/mask;
                }

                /* now do the allgather */

                mask >>= 1;
                while (mask > 0) {
                    newdst = newrank ^ mask;
                    /* find real rank of dest */
                    dst = (newdst < rem) ? newdst*2 + 1 : newdst + rem;

                    send_cnt = recv_cnt = 0;
                    if (newrank < newdst) {
                        /* update last_idx except on first iteration */
                        if (mask != pof2/2)
                            last_idx = last_idx + pof2/(mask*2);

                        recv_idx = send_idx + pof2/(mask*2);
                        for (i=send_idx; i<recv_idx; i++)
                            send_cnt += cnts[i];
                        for (i=recv_idx; i<last_idx; i++)
                            recv_cnt += cnts[i];
                    }
                    else {
                        recv_idx = send_idx - pof2/(mask*2);
                        for (i=send_idx; i<last_idx; i++)
                            send_cnt += cnts[i];
                        for (i=recv_idx; i<send_idx; i++)
                            recv_cnt += cnts[i];
                    }

498
499
500
501
502
503
504
505
506
                    mpi_errno = MPIC_Sendrecv_ft((char *) recvbuf +
                                                 disps[send_idx]*extent,
                                                 send_cnt, datatype,  
                                                 dst, MPIR_ALLREDUCE_TAG, 
                                                 (char *) recvbuf +
                                                 disps[recv_idx]*extent,
                                                 recv_cnt, datatype, dst,
                                                 MPIR_ALLREDUCE_TAG, comm,
                                                 MPI_STATUS_IGNORE, errflag);
507
508
                    if (mpi_errno) {
                        /* for communication errors, just record the error but continue */
509
                        *errflag = TRUE;
510
511
512
                        MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                        MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
                    }
513
514
515
516
517
518
519
520
521
522
523
524
525

                    if (newrank > newdst) send_idx = recv_idx;

                    mask >>= 1;
                }
            }
        }

        /* In the non-power-of-two case, all odd-numbered
           processes of rank < 2*rem send the result to
           (rank-1), the ranks who didn't participate above. */
        if (rank < 2*rem) {
            if (rank % 2)  /* odd */
526
527
528
                mpi_errno = MPIC_Send_ft(recvbuf, count, 
                                         datatype, rank-1,
                                         MPIR_ALLREDUCE_TAG, comm, errflag);
529
            else  /* even */
530
531
532
533
                mpi_errno = MPIC_Recv_ft(recvbuf, count,
                                         datatype, rank+1,
                                         MPIR_ALLREDUCE_TAG, comm,
                                         MPI_STATUS_IGNORE, errflag);
534
535
            if (mpi_errno) {
                /* for communication errors, just record the error but continue */
536
                *errflag = TRUE;
537
538
539
                MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
                MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
            }
540
541
542
543
        }
    }

  fn_exit:
544
545
546
    /* check if multiple threads are calling this collective function */
    MPIDU_ERR_CHECK_MULTIPLE_THREADS_EXIT( comm_ptr );

547
    MPIU_CHKLMEM_FREEALL();
548
549
    if (mpi_errno_ret)
        mpi_errno = mpi_errno_ret;
550
551
552
553
554
555
556
557
558
    return (mpi_errno);

  fn_fail:
    goto fn_exit;
}


/* not declared static because a machine-specific function may call this one 
   in some cases */
559
560
#undef FUNCNAME
#define FUNCNAME MPIR_Allreduce_inter
561
#undef FCNAME
562
#define FCNAME MPIU_QUOTE(FUNCNAME)
563
int MPIR_Allreduce_inter ( 
564
    const void *sendbuf,
565
566
567
568
    void *recvbuf, 
    int count, 
    MPI_Datatype datatype, 
    MPI_Op op, 
569
570
    MPID_Comm *comm_ptr,
    int *errflag )
571
572
573
574
575
576
577
578
579
580
{
/* Intercommunicator Allreduce.
   We first do an intercommunicator reduce to rank 0 on left group,
   then an intercommunicator reduce to rank 0 on right group, followed
   by local intracommunicator broadcasts in each group.

   We don't do local reduces first and then intercommunicator
   broadcasts because it would require allocation of a temporary buffer. 
*/
    int rank, mpi_errno, root;
581
    int mpi_errno_ret = MPI_SUCCESS;
582
583
584
585
586
587
588
589
590
591
    MPID_Comm *newcomm_ptr = NULL;
    
    rank = comm_ptr->rank;

    /* first do a reduce from right group to rank 0 in left group,
       then from left group to rank 0 in right group*/
    if (comm_ptr->is_low_group) {
        /* reduce from right group to rank 0*/
        root = (rank == 0) ? MPI_ROOT : MPI_PROC_NULL;
        mpi_errno = MPIR_Reduce_inter(sendbuf, recvbuf, count, datatype, op,
592
				      root, comm_ptr, errflag);
593
594
        if (mpi_errno) {
            /* for communication errors, just record the error but continue */
595
            *errflag = TRUE;
596
597
598
            MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
            MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
        }
599
600
601
602

        /* reduce to rank 0 of right group */
        root = 0;
        mpi_errno = MPIR_Reduce_inter(sendbuf, recvbuf, count, datatype, op,
603
				      root, comm_ptr, errflag);
604
605
        if (mpi_errno) {
            /* for communication errors, just record the error but continue */
606
            *errflag = TRUE;
607
608
609
            MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
            MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
        }
610
611
612
613
614
    }
    else {
        /* reduce to rank 0 of left group */
        root = 0;
        mpi_errno = MPIR_Reduce_inter(sendbuf, recvbuf, count, datatype, op,
615
				      root, comm_ptr, errflag);
616
617
        if (mpi_errno) {
            /* for communication errors, just record the error but continue */
618
            *errflag = TRUE;
619
620
621
            MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
            MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
        }
622
623
624
625

        /* reduce from right group to rank 0 */
        root = (rank == 0) ? MPI_ROOT : MPI_PROC_NULL;
        mpi_errno = MPIR_Reduce_inter(sendbuf, recvbuf, count, datatype, op,
626
				      root, comm_ptr, errflag);
627
628
        if (mpi_errno) {
            /* for communication errors, just record the error but continue */
629
            *errflag = TRUE;
630
631
632
            MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
            MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
        }
633
634
635
636
637
638
639
640
    }

    /* Get the local intracommunicator */
    if (!comm_ptr->local_comm)
	MPIR_Setup_intercomm_localcomm( comm_ptr );

    newcomm_ptr = comm_ptr->local_comm;

641
    mpi_errno = MPIR_Bcast_impl(recvbuf, count, datatype, 0, newcomm_ptr, errflag);
642
643
    if (mpi_errno) {
        /* for communication errors, just record the error but continue */
644
        *errflag = TRUE;
645
646
647
        MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**fail");
        MPIU_ERR_ADD(mpi_errno_ret, mpi_errno);
    }
648

649
  fn_exit:
650
651
    if (mpi_errno_ret)
        mpi_errno = mpi_errno_ret;
652
653
654
    else if (*errflag)
        MPIU_ERR_SET(mpi_errno, MPI_ERR_OTHER, "**coll_fail");

655
    return mpi_errno;
656
657
658

  fn_fail:
    goto fn_exit;
659
660
}

661
662
663
664
665
666
667
668
/* MPIR_Allreduce performs an allreduce using point-to-point messages.
   This is intended to be used by device-specific implementations of
   allreduce.  In all other cases MPIR_Allreduce_impl should be
   used. */
#undef FUNCNAME
#define FUNCNAME MPIR_Allreduce
#undef FCNAME
#define FCNAME MPIU_QUOTE(FUNCNAME)
669
670
int MPIR_Allreduce(const void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype,
                   MPI_Op op, MPID_Comm *comm_ptr, int *errflag)
671
672
673
674
675
{
    int mpi_errno = MPI_SUCCESS;

    if (comm_ptr->comm_kind == MPID_INTRACOMM) {
        /* intracommunicator */
676
        mpi_errno = MPIR_Allreduce_intra(sendbuf, recvbuf, count, datatype, op, comm_ptr, errflag);
677
678
679
680
        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
    }
    else {
        /* intercommunicator */
681
        mpi_errno = MPIR_Allreduce_inter(sendbuf, recvbuf, count, datatype, op, comm_ptr, errflag);
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
    }

fn_exit:
    return mpi_errno;
fn_fail:

    goto fn_exit;
}

/* MPIR_Allreduce_impl should be called by any internal component that
   would otherwise call MPI_Allreduce.  This differs from
   MPIR_Allreduce in that this will call the coll_fns version if it
   exists.  */
#undef FUNCNAME
#define FUNCNAME MPIR_Allreduce_impl
#undef FCNAME
#define FCNAME MPIU_QUOTE(FUNCNAME)
700
int MPIR_Allreduce_impl(const void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype, MPI_Op op, MPID_Comm *comm_ptr,
701
                        int *errflag)
702
703
704
705
706
{
    int mpi_errno = MPI_SUCCESS;

    if (comm_ptr->coll_fns != NULL && comm_ptr->coll_fns->Allreduce != NULL)
    {
707
	/* --BEGIN USEREXTENSION-- */
708
	mpi_errno = comm_ptr->coll_fns->Allreduce(sendbuf, recvbuf, count, datatype, op, comm_ptr, errflag);
709
        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
710
	/* --END USEREXTENSION-- */
711
712
713
714
715
    }
    else
    {
        if (comm_ptr->comm_kind == MPID_INTRACOMM) {
            /* intracommunicator */
716
            mpi_errno = MPIR_Allreduce_intra(sendbuf, recvbuf, count, datatype, op, comm_ptr, errflag);
717
            if (mpi_errno) MPIU_ERR_POP(mpi_errno);
718
719
720
	}
        else {
            /* intercommunicator */
721
            mpi_errno = MPIR_Allreduce_inter(sendbuf, recvbuf, count, datatype, op, comm_ptr, errflag);
722
            if (mpi_errno) MPIU_ERR_POP(mpi_errno);
723
724
725
726
727
728
729
730
731
732
        }
    }

fn_exit:
    return mpi_errno;
fn_fail:
    goto fn_exit;
}


733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
#endif

#undef FUNCNAME
#define FUNCNAME MPI_Allreduce
#undef FCNAME

/*@
MPI_Allreduce - Combines values from all processes and distributes the result
                back to all processes

Input Parameters:
+ sendbuf - starting address of send buffer (choice) 
. count - number of elements in send buffer (integer) 
. datatype - data type of elements of send buffer (handle) 
. op - operation (handle) 
- comm - communicator (handle) 

Output Parameter:
. recvbuf - starting address of receive buffer (choice) 

.N ThreadSafe

.N Fortran

.N collops

.N Errors
.N MPI_ERR_BUFFER
.N MPI_ERR_COUNT
.N MPI_ERR_TYPE
.N MPI_ERR_OP
.N MPI_ERR_COMM
@*/
766
767
int MPI_Allreduce(MPICH2_CONST void *sendbuf, void *recvbuf, int count,
                  MPI_Datatype datatype, MPI_Op op, MPI_Comm comm)
768
769
770
771
{
    static const char FCNAME[] = "MPI_Allreduce";
    int mpi_errno = MPI_SUCCESS;
    MPID_Comm *comm_ptr = NULL;
772
    int errflag = FALSE;
773
774
775
776
    MPID_MPI_STATE_DECL(MPID_STATE_MPI_ALLREDUCE);

    MPIR_ERRTEST_INITIALIZED_ORDIE();
    
777
    MPIU_THREAD_CS_ENTER(ALLFUNC,);
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
    MPID_MPI_COLL_FUNC_ENTER(MPID_STATE_MPI_ALLREDUCE);

    /* Validate parameters, especially handles needing to be converted */
#   ifdef HAVE_ERROR_CHECKING
    {
        MPID_BEGIN_ERROR_CHECKS;
        {
	    MPIR_ERRTEST_COMM(comm, mpi_errno);
            if (mpi_errno != MPI_SUCCESS) goto fn_fail;
	}
        MPID_END_ERROR_CHECKS;
    }
#   endif /* HAVE_ERROR_CHECKING */

    /* Convert MPI object handles to object pointers */
    MPID_Comm_get_ptr( comm, comm_ptr );

    /* Validate parameters and objects (post conversion) */
#   ifdef HAVE_ERROR_CHECKING
    {
        MPID_BEGIN_ERROR_CHECKS;
        {
            MPID_Datatype *datatype_ptr = NULL;
            MPID_Op *op_ptr = NULL;

            MPID_Comm_valid_ptr( comm_ptr, mpi_errno );
            if (mpi_errno != MPI_SUCCESS) goto fn_fail;
	    MPIR_ERRTEST_COUNT(count, mpi_errno);
	    MPIR_ERRTEST_DATATYPE(datatype, "datatype", mpi_errno);
	    MPIR_ERRTEST_OP(op, mpi_errno);
	    
            if (HANDLE_GET_KIND(datatype) != HANDLE_KIND_BUILTIN) {
                MPID_Datatype_get_ptr(datatype, datatype_ptr);
                MPID_Datatype_valid_ptr( datatype_ptr, mpi_errno );
                MPID_Datatype_committed_ptr( datatype_ptr, mpi_errno );
            }

	    if (comm_ptr->comm_kind == MPID_INTERCOMM)
                MPIR_ERRTEST_SENDBUF_INPLACE(sendbuf, count, mpi_errno);
            
            if (sendbuf != MPI_IN_PLACE) 
                MPIR_ERRTEST_USERBUFFER(sendbuf,count,datatype,mpi_errno);

            MPIR_ERRTEST_RECVBUF_INPLACE(recvbuf, count, mpi_errno);
	    MPIR_ERRTEST_USERBUFFER(recvbuf,count,datatype,mpi_errno);

	    if (mpi_errno != MPI_SUCCESS) goto fn_fail;

            if (HANDLE_GET_KIND(op) != HANDLE_KIND_BUILTIN) {
                MPID_Op_get_ptr(op, op_ptr);
                MPID_Op_valid_ptr( op_ptr, mpi_errno );
            }
            if (HANDLE_GET_KIND(op) == HANDLE_KIND_BUILTIN) {
                mpi_errno = 
832
                    ( * MPIR_OP_HDL_TO_DTYPE_FN(op) )(datatype); 
833
            }
834
835
836
	    if (count != 0) {
		MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno);
	    }
837
	    if (mpi_errno != MPI_SUCCESS) goto fn_fail;
838
	}
839
840
841
842
843
844
        MPID_END_ERROR_CHECKS;
    }
#   endif /* HAVE_ERROR_CHECKING */

    /* ... body of routine ...  */

845
    mpi_errno = MPIR_Allreduce_impl(sendbuf, recvbuf, count, datatype, op, comm_ptr, &errflag);
846
    if (mpi_errno) goto fn_fail;
847
848
849
850
851

    /* ... end of body of routine ... */
    
  fn_exit:
    MPID_MPI_COLL_FUNC_EXIT(MPID_STATE_MPI_ALLREDUCE);
852
    MPIU_THREAD_CS_EXIT(ALLFUNC,);
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
    return mpi_errno;

  fn_fail:
    /* --BEGIN ERROR HANDLING-- */
#   ifdef HAVE_ERROR_CHECKING
    {
	mpi_errno = MPIR_Err_create_code(
	    mpi_errno, MPIR_ERR_RECOVERABLE, FCNAME, __LINE__, MPI_ERR_OTHER, "**mpi_allreduce",
	    "**mpi_allreduce %p %p %d %D %O %C", sendbuf, recvbuf, count, datatype, op, comm);
    }
#   endif
    mpi_errno = MPIR_Err_return_comm( comm_ptr, FCNAME, mpi_errno );
    goto fn_exit;
    /* --END ERROR HANDLING-- */
}