Date: 2025-03-29T05:58:52+00:00

Actual source code: sfallgatherv.c

      1: #include <../src/vec/is/sf/impls/basic/allgatherv/sfallgatherv.h>

      3: /* PetscSFGetGraph is non-collective. An implementation should not have collective calls */
      4: PETSC_INTERN PetscErrorCode PetscSFGetGraph_Allgatherv(PetscSF sf, PetscInt *nroots, PetscInt *nleaves, const PetscInt **ilocal, const PetscSFNode **iremote)
      5: {
      6:   PetscInt        j, k;
      7:   const PetscInt *range;
      8:   PetscMPIInt     size;

     10:   PetscFunctionBegin;
     11:   PetscCallMPI(MPI_Comm_size(PetscObjectComm((PetscObject)sf), &size));
     12:   if (nroots) *nroots = sf->nroots;
     13:   if (nleaves) *nleaves = sf->nleaves;
     14:   if (ilocal) *ilocal = NULL; /* Contiguous leaves */
     15:   if (iremote) {
     16:     if (!sf->remote && sf->nleaves) { /* The && sf->nleaves makes sfgatherv able to inherit this routine */
     17:       PetscCall(PetscLayoutGetRanges(sf->map, &range));
     18:       PetscCall(PetscMalloc1(sf->nleaves, &sf->remote));
     19:       sf->remote_alloc = sf->remote;
     20:       for (PetscMPIInt i = 0; i < size; i++) {
     21:         for (j = range[i], k = 0; j < range[i + 1]; j++, k++) {
     22:           sf->remote[j].rank  = i;
     23:           sf->remote[j].index = k;
     24:         }
     25:       }
     26:     }
     27:     *iremote = sf->remote;
     28:   }
     29:   PetscFunctionReturn(PETSC_SUCCESS);
     30: }

     32: PETSC_INTERN PetscErrorCode PetscSFSetUp_Allgatherv(PetscSF sf)
     33: {
     34:   PetscSF_Allgatherv *dat = (PetscSF_Allgatherv *)sf->data;
     35:   PetscMPIInt         size;
     36:   PetscInt            i;
     37:   const PetscInt     *range;
     38:   MPI_Comm            comm;

     40:   PetscFunctionBegin;
     41:   PetscCall(PetscSFSetUp_Allgather(sf));
     42:   PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
     43:   PetscCallMPI(MPI_Comm_size(comm, &size));
     44:   if (sf->nleaves) { /* This if (sf->nleaves) test makes sfgatherv able to inherit this routine */
     45:     PetscBool isallgatherv = PETSC_FALSE;

     47:     PetscCall(PetscMalloc1(size, &dat->recvcounts));
     48:     PetscCall(PetscMalloc1(size, &dat->displs));
     49:     PetscCall(PetscLayoutGetRanges(sf->map, &range));

     51:     for (i = 0; i < size; i++) {
     52:       PetscCall(PetscMPIIntCast(range[i], &dat->displs[i]));
     53:       PetscCall(PetscMPIIntCast(range[i + 1] - range[i], &dat->recvcounts[i]));
     54:     }

     56:     /* check if we actually have a one-to-all pattern */
     57:     PetscCall(PetscObjectTypeCompare((PetscObject)sf, PETSCSFALLGATHERV, &isallgatherv));
     58:     if (isallgatherv) {
     59:       PetscMPIInt rank, nRanksWithZeroRoots;

     61:       nRanksWithZeroRoots = (sf->nroots == 0) ? 1 : 0; /* I have no roots */
     62:       PetscCallMPI(MPIU_Allreduce(MPI_IN_PLACE, &nRanksWithZeroRoots, 1, MPI_INT, MPI_SUM, comm));
     63:       if (nRanksWithZeroRoots == size - 1) { /* Only one rank has roots, which indicates a bcast pattern */
     64:         dat->bcast_pattern = PETSC_TRUE;
     65:         PetscCallMPI(MPI_Comm_rank(comm, &rank));
     66:         dat->bcast_root = sf->nroots > 0 ? rank : -1;
     67:         PetscCallMPI(MPIU_Allreduce(MPI_IN_PLACE, &dat->bcast_root, 1, MPI_INT, MPI_MAX, comm));
     68:       }
     69:     }
     70:   }
     71:   PetscFunctionReturn(PETSC_SUCCESS);
     72: }

     74: PETSC_INTERN PetscErrorCode PetscSFReset_Allgatherv(PetscSF sf)
     75: {
     76:   PetscSF_Allgatherv *dat  = (PetscSF_Allgatherv *)sf->data;
     77:   PetscSFLink         link = dat->avail, next;

     79:   PetscFunctionBegin;
     80:   PetscCall(PetscFree(dat->iranks));
     81:   PetscCall(PetscFree(dat->ioffset));
     82:   PetscCall(PetscFree(dat->irootloc));
     83:   PetscCall(PetscFree(dat->recvcounts));
     84:   PetscCall(PetscFree(dat->displs));
     85:   PetscCheck(!dat->inuse, PetscObjectComm((PetscObject)sf), PETSC_ERR_ARG_WRONGSTATE, "Outstanding operation has not been completed");
     86:   for (; link; link = next) {
     87:     next = link->next;
     88:     PetscCall(PetscSFLinkDestroy(sf, link));
     89:   }
     90:   dat->avail = NULL;
     91:   PetscFunctionReturn(PETSC_SUCCESS);
     92: }

     94: PETSC_INTERN PetscErrorCode PetscSFDestroy_Allgatherv(PetscSF sf)
     95: {
     96:   PetscFunctionBegin;
     97:   PetscCall(PetscSFReset_Allgatherv(sf));
     98:   PetscCall(PetscFree(sf->data));
     99:   PetscFunctionReturn(PETSC_SUCCESS);
    100: }

    102: static PetscErrorCode PetscSFBcastBegin_Allgatherv(PetscSF sf, MPI_Datatype unit, PetscMemType rootmtype, const void *rootdata, PetscMemType leafmtype, void *leafdata, MPI_Op op)
    103: {
    104:   PetscSFLink         link;
    105:   PetscMPIInt         sendcount, rank, nleaves;
    106:   MPI_Comm            comm;
    107:   void               *rootbuf = NULL, *leafbuf = NULL;
    108:   MPI_Request        *req = NULL;
    109:   PetscSF_Allgatherv *dat = (PetscSF_Allgatherv *)sf->data;

    111:   PetscFunctionBegin;
    112:   PetscCall(PetscSFLinkCreate(sf, unit, rootmtype, rootdata, leafmtype, leafdata, op, PETSCSF_BCAST, &link));
    113:   PetscCall(PetscSFLinkPackRootData(sf, link, PETSCSF_REMOTE, rootdata));
    114:   PetscCall(PetscSFLinkCopyRootBufferInCaseNotUseGpuAwareMPI(sf, link, PETSC_TRUE /* device2host before sending */));
    115:   PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
    116:   PetscCallMPI(MPI_Comm_rank(comm, &rank));
    117:   PetscCall(PetscMPIIntCast(sf->nroots, &sendcount));
    118:   PetscCall(PetscSFLinkGetMPIBuffersAndRequests(sf, link, PETSCSF_ROOT2LEAF, &rootbuf, &leafbuf, &req, NULL));

    120:   if (dat->bcast_pattern && rank == dat->bcast_root) PetscCall((*link->Memcpy)(link, link->leafmtype_mpi, leafbuf, link->rootmtype_mpi, rootbuf, (size_t)sendcount * link->unitbytes));
    121:   /* Ready the buffers for MPI */
    122:   PetscCall(PetscSFLinkSyncStreamBeforeCallMPI(sf, link));
    123:   PetscCall(PetscMPIIntCast(sf->nleaves, &nleaves));
    124:   if (dat->bcast_pattern) PetscCallMPI(MPIU_Ibcast(leafbuf, nleaves, unit, dat->bcast_root, comm, req));
    125:   else PetscCallMPI(MPIU_Iallgatherv(rootbuf, sendcount, unit, leafbuf, dat->recvcounts, dat->displs, unit, comm, req));
    126:   PetscFunctionReturn(PETSC_SUCCESS);
    127: }

    129: static PetscErrorCode PetscSFReduceBegin_Allgatherv(PetscSF sf, MPI_Datatype unit, PetscMemType leafmtype, const void *leafdata, PetscMemType rootmtype, void *rootdata, MPI_Op op)
    130: {
    131:   PetscSFLink         link;
    132:   PetscSF_Allgatherv *dat = (PetscSF_Allgatherv *)sf->data;
    133:   PetscInt            rstart;
    134:   PetscMPIInt         rank, count, recvcount;
    135:   MPI_Comm            comm;
    136:   void               *rootbuf = NULL, *leafbuf = NULL;
    137:   MPI_Request        *req = NULL;

    139:   PetscFunctionBegin;
    140:   PetscCall(PetscSFLinkCreate(sf, unit, rootmtype, rootdata, leafmtype, leafdata, op, PETSCSF_REDUCE, &link));
    141:   if (op == MPI_REPLACE) {
    142:     /* REPLACE is only meaningful when all processes have the same leafdata to reduce. Therefore copying from local leafdata is fine */
    143:     PetscCall(PetscLayoutGetRange(sf->map, &rstart, NULL));
    144:     PetscCall((*link->Memcpy)(link, rootmtype, rootdata, leafmtype, (const char *)leafdata + (size_t)rstart * link->unitbytes, (size_t)sf->nroots * link->unitbytes));
    145:     if (PetscMemTypeDevice(leafmtype) && PetscMemTypeHost(rootmtype)) PetscCall((*link->SyncStream)(link));
    146:   } else {
    147:     PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
    148:     PetscCall(PetscSFLinkPackLeafData(sf, link, PETSCSF_REMOTE, leafdata));
    149:     PetscCall(PetscSFLinkCopyLeafBufferInCaseNotUseGpuAwareMPI(sf, link, PETSC_TRUE /* device2host before sending */));
    150:     PetscCall(PetscSFLinkGetMPIBuffersAndRequests(sf, link, PETSCSF_LEAF2ROOT, &rootbuf, &leafbuf, &req, NULL));
    151:     PetscCall(PetscSFLinkSyncStreamBeforeCallMPI(sf, link));
    152:     if (dat->bcast_pattern) {
    153:       PetscMPIInt nleavesi;

    155:       PetscCall(PetscMPIIntCast(sf->nleaves, &nleavesi));
    156: #if defined(PETSC_HAVE_OPENMPI) /* Workaround: cuda-aware Open MPI 4.1.3 does not support MPI_Ireduce() with device buffers */
    157:       *req = MPI_REQUEST_NULL;  /* Set NULL so that we can safely MPI_Wait(req) */
    158:       PetscCallMPI(MPIU_Reduce(leafbuf, rootbuf, nleavesi, unit, op, dat->bcast_root, comm));
    159: #else
    160:       PetscCallMPI(MPIU_Ireduce(leafbuf, rootbuf, nleavesi, unit, op, dat->bcast_root, comm, req));
    161: #endif
    162:     } else { /* Reduce leafdata, then scatter to rootdata */
    163:       PetscCallMPI(MPI_Comm_rank(comm, &rank));
    164:       PetscCall(PetscMPIIntCast(dat->rootbuflen[PETSCSF_REMOTE], &recvcount));
    165:       /* Allocate a separate leaf buffer on rank 0 */
    166:       if (rank == 0 && !link->leafbuf_alloc[PETSCSF_REMOTE][link->leafmtype_mpi]) {
    167:         PetscCall(PetscSFMalloc(sf, link->leafmtype_mpi, sf->leafbuflen[PETSCSF_REMOTE] * link->unitbytes, (void **)&link->leafbuf_alloc[PETSCSF_REMOTE][link->leafmtype_mpi]));
    168:       }
    169:       /* In case we already copied leafdata from device to host (i.e., no use_gpu_aware_mpi), we need to adjust leafbuf on rank 0 */
    170:       if (rank == 0 && link->leafbuf_alloc[PETSCSF_REMOTE][link->leafmtype_mpi] == leafbuf) leafbuf = MPI_IN_PLACE;
    171:       PetscCall(PetscMPIIntCast(sf->nleaves * link->bs, &count));
    172:       PetscCallMPI(MPI_Reduce(leafbuf, link->leafbuf_alloc[PETSCSF_REMOTE][link->leafmtype_mpi], count, link->basicunit, op, 0, comm)); /* Must do reduce with MPI builtin datatype basicunit */
    173:       PetscCallMPI(MPIU_Iscatterv(link->leafbuf_alloc[PETSCSF_REMOTE][link->leafmtype_mpi], dat->recvcounts, dat->displs, unit, rootbuf, recvcount, unit, 0, comm, req));
    174:     }
    175:   }
    176:   PetscFunctionReturn(PETSC_SUCCESS);
    177: }

    179: PETSC_INTERN PetscErrorCode PetscSFReduceEnd_Allgatherv(PetscSF sf, MPI_Datatype unit, const void *leafdata, void *rootdata, MPI_Op op)
    180: {
    181:   PetscSFLink link;

    183:   PetscFunctionBegin;
    184:   if (op == MPI_REPLACE) {
    185:     /* A rare case happens when op is MPI_REPLACE, using GPUs but no GPU aware MPI. In PetscSFReduceBegin_Allgather(v),
    186:       we did a device to device copy and in effect finished the communication. But in PetscSFLinkFinishCommunication()
    187:       of PetscSFReduceEnd_Basic(), it thinks since there is rootbuf, it calls PetscSFLinkCopyRootBufferInCaseNotUseGpuAwareMPI().
    188:       It does a host to device memory copy on rootbuf, wrongly overwriting the results. So we don't overload
    189:       PetscSFReduceEnd_Basic() in this case, and just reclaim the link.
    190:      */
    191:     PetscCall(PetscSFLinkGetInUse(sf, unit, rootdata, leafdata, PETSC_OWN_POINTER, &link));
    192:     PetscCall(PetscSFLinkReclaim(sf, &link));
    193:   } else {
    194:     PetscCall(PetscSFReduceEnd_Basic(sf, unit, leafdata, rootdata, op));
    195:   }
    196:   PetscFunctionReturn(PETSC_SUCCESS);
    197: }

    199: static PetscErrorCode PetscSFBcastToZero_Allgatherv(PetscSF sf, MPI_Datatype unit, PetscMemType rootmtype, const void *rootdata, PetscMemType leafmtype, void *leafdata)
    200: {
    201:   PetscSFLink         link;
    202:   PetscMPIInt         rank;
    203:   PetscMPIInt         sendcount;
    204:   MPI_Comm            comm;
    205:   PetscSF_Allgatherv *dat     = (PetscSF_Allgatherv *)sf->data;
    206:   void               *rootbuf = NULL, *leafbuf = NULL; /* buffer seen by MPI */
    207:   MPI_Request        *req = NULL;

    209:   PetscFunctionBegin;
    210:   PetscCall(PetscSFLinkCreate(sf, unit, rootmtype, rootdata, leafmtype, leafdata, MPI_REPLACE, PETSCSF_BCAST, &link));
    211:   PetscCall(PetscSFLinkPackRootData(sf, link, PETSCSF_REMOTE, rootdata));
    212:   PetscCall(PetscSFLinkCopyRootBufferInCaseNotUseGpuAwareMPI(sf, link, PETSC_TRUE /* device2host before sending */));
    213:   PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
    214:   PetscCall(PetscMPIIntCast(sf->nroots, &sendcount));
    215:   PetscCall(PetscSFLinkGetMPIBuffersAndRequests(sf, link, PETSCSF_ROOT2LEAF, &rootbuf, &leafbuf, &req, NULL));
    216:   PetscCall(PetscSFLinkSyncStreamBeforeCallMPI(sf, link));
    217:   PetscCallMPI(MPIU_Igatherv(rootbuf, sendcount, unit, leafbuf, dat->recvcounts, dat->displs, unit, 0 /*rank 0*/, comm, req));

    219:   PetscCall(PetscSFLinkGetInUse(sf, unit, rootdata, leafdata, PETSC_OWN_POINTER, &link));
    220:   PetscCall(PetscSFLinkFinishCommunication(sf, link, PETSCSF_ROOT2LEAF));
    221:   PetscCallMPI(MPI_Comm_rank(PetscObjectComm((PetscObject)sf), &rank));
    222:   if (rank == 0 && PetscMemTypeDevice(leafmtype) && !sf->use_gpu_aware_mpi) PetscCall((*link->Memcpy)(link, PETSC_MEMTYPE_DEVICE, leafdata, PETSC_MEMTYPE_HOST, link->leafbuf[PETSC_MEMTYPE_HOST], sf->leafbuflen[PETSCSF_REMOTE] * link->unitbytes));
    223:   PetscCall(PetscSFLinkReclaim(sf, &link));
    224:   PetscFunctionReturn(PETSC_SUCCESS);
    225: }

    227: /* This routine is very tricky (I believe it is rarely used with this kind of graph so just provide a simple but not-optimal implementation).

    229:    Suppose we have three ranks. Rank 0 has a root with value 1. Rank 0,1,2 has a leaf with value 2,3,4 respectively. The leaves are connected
    230:    to the root on rank 0. Suppose op=MPI_SUM and rank 0,1,2 gets root state in their rank order. By definition of this routine, rank 0 sees 1
    231:    in root, fetches it into its leafupate, then updates root to 1 + 2 = 3; rank 1 sees 3 in root, fetches it into its leafupate, then updates
    232:    root to 3 + 3 = 6; rank 2 sees 6 in root, fetches it into its leafupdate, then updates root to 6 + 4 = 10.  At the end, leafupdate on rank
    233:    0,1,2 is 1,3,6 respectively. root is 10.

    235:    We use a simpler implementation. From the same initial state, we copy leafdata to leafupdate
    236:              rank-0   rank-1    rank-2
    237:         Root     1
    238:         Leaf     2       3         4
    239:      Leafupdate  2       3         4

    241:    Do MPI_Exscan on leafupdate,
    242:              rank-0   rank-1    rank-2
    243:         Root     1
    244:         Leaf     2       3         4
    245:      Leafupdate  2       2         5

    247:    BcastAndOp from root to leafupdate,
    248:              rank-0   rank-1    rank-2
    249:         Root     1
    250:         Leaf     2       3         4
    251:      Leafupdate  3       3         6

    253:    Copy root to leafupdate on rank-0
    254:              rank-0   rank-1    rank-2
    255:         Root     1
    256:         Leaf     2       3         4
    257:      Leafupdate  1       3         6

    259:    Reduce from leaf to root,
    260:              rank-0   rank-1    rank-2
    261:         Root     10
    262:         Leaf     2       3         4
    263:      Leafupdate  1       3         6
    264: */
    265: PETSC_INTERN PetscErrorCode PetscSFFetchAndOpBegin_Allgatherv(PetscSF sf, MPI_Datatype unit, PetscMemType rootmtype, void *rootdata, PetscMemType leafmtype, const void *leafdata, void *leafupdate, MPI_Op op)
    266: {
    267:   PetscSFLink link;
    268:   MPI_Comm    comm;
    269:   PetscMPIInt count;

    271:   PetscFunctionBegin;
    272:   PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
    273:   PetscCheck(!PetscMemTypeDevice(rootmtype) && !PetscMemTypeDevice(leafmtype), comm, PETSC_ERR_SUP, "Do FetchAndOp on device");
    274:   /* Copy leafdata to leafupdate */
    275:   PetscCall(PetscSFLinkCreate(sf, unit, rootmtype, rootdata, leafmtype, leafdata, op, PETSCSF_FETCH, &link));
    276:   PetscCall(PetscSFLinkPackLeafData(sf, link, PETSCSF_REMOTE, leafdata)); /* Sync the device */
    277:   PetscCall((*link->Memcpy)(link, leafmtype, leafupdate, leafmtype, leafdata, sf->nleaves * link->unitbytes));
    278:   PetscCall(PetscSFLinkGetInUse(sf, unit, rootdata, leafdata, PETSC_OWN_POINTER, &link));

    280:   /* Exscan on leafupdate and then BcastAndOp rootdata to leafupdate */
    281:   if (op == MPI_REPLACE) {
    282:     PetscMPIInt size, rank, prev, next;
    283:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
    284:     PetscCallMPI(MPI_Comm_size(comm, &size));
    285:     prev = rank ? rank - 1 : MPI_PROC_NULL;
    286:     next = (rank < size - 1) ? rank + 1 : MPI_PROC_NULL;
    287:     PetscCall(PetscMPIIntCast(sf->nleaves, &count));
    288:     PetscCallMPI(MPI_Sendrecv_replace(leafupdate, count, unit, next, link->tag, prev, link->tag, comm, MPI_STATUSES_IGNORE));
    289:   } else {
    290:     PetscCall(PetscMPIIntCast(sf->nleaves * link->bs, &count));
    291:     PetscCallMPI(MPI_Exscan(MPI_IN_PLACE, leafupdate, count, link->basicunit, op, comm));
    292:   }
    293:   PetscCall(PetscSFLinkReclaim(sf, &link));
    294:   PetscCall(PetscSFBcastBegin(sf, unit, rootdata, leafupdate, op));
    295:   PetscCall(PetscSFBcastEnd(sf, unit, rootdata, leafupdate, op));

    297:   /* Bcast roots to rank 0's leafupdate */
    298:   PetscCall(PetscSFBcastToZero_Private(sf, unit, rootdata, leafupdate)); /* Using this line makes Allgather SFs able to inherit this routine */

    300:   /* Reduce leafdata to rootdata */
    301:   PetscCall(PetscSFReduceBegin(sf, unit, leafdata, rootdata, op));
    302:   PetscFunctionReturn(PETSC_SUCCESS);
    303: }

    305: PETSC_INTERN PetscErrorCode PetscSFFetchAndOpEnd_Allgatherv(PetscSF sf, MPI_Datatype unit, void *rootdata, const void *leafdata, void *leafupdate, MPI_Op op)
    306: {
    307:   PetscFunctionBegin;
    308:   PetscCall(PetscSFReduceEnd(sf, unit, leafdata, rootdata, op));
    309:   PetscFunctionReturn(PETSC_SUCCESS);
    310: }

    312: /* Get root ranks accessing my leaves */
    313: PETSC_INTERN PetscErrorCode PetscSFGetRootRanks_Allgatherv(PetscSF sf, PetscMPIInt *nranks, const PetscMPIInt **ranks, const PetscInt **roffset, const PetscInt **rmine, const PetscInt **rremote)
    314: {
    315:   PetscInt        j, k, size;
    316:   const PetscInt *range;

    318:   PetscFunctionBegin;
    319:   /* Lazily construct these large arrays if users really need them for this type of SF. Very likely, they do not */
    320:   if (sf->nranks && !sf->ranks) { /* On rank!=0, sf->nranks=0. The sf->nranks test makes this routine also works for sfgatherv */
    321:     size = sf->nranks;
    322:     PetscCall(PetscLayoutGetRanges(sf->map, &range));
    323:     PetscCall(PetscMalloc4(size, &sf->ranks, size + 1, &sf->roffset, sf->nleaves, &sf->rmine, sf->nleaves, &sf->rremote));
    324:     for (PetscMPIInt i = 0; i < size; i++) sf->ranks[i] = i;
    325:     PetscCall(PetscArraycpy(sf->roffset, range, size + 1));
    326:     for (PetscInt i = 0; i < sf->nleaves; i++) sf->rmine[i] = i; /*rmine are never NULL even for contiguous leaves */
    327:     for (PetscMPIInt i = 0; i < size; i++) {
    328:       for (j = range[i], k = 0; j < range[i + 1]; j++, k++) sf->rremote[j] = k;
    329:     }
    330:   }

    332:   if (nranks) *nranks = sf->nranks;
    333:   if (ranks) *ranks = sf->ranks;
    334:   if (roffset) *roffset = sf->roffset;
    335:   if (rmine) *rmine = sf->rmine;
    336:   if (rremote) *rremote = sf->rremote;
    337:   PetscFunctionReturn(PETSC_SUCCESS);
    338: }

    340: /* Get leaf ranks accessing my roots */
    341: PETSC_INTERN PetscErrorCode PetscSFGetLeafRanks_Allgatherv(PetscSF sf, PetscMPIInt *niranks, const PetscMPIInt **iranks, const PetscInt **ioffset, const PetscInt **irootloc)
    342: {
    343:   PetscSF_Allgatherv *dat = (PetscSF_Allgatherv *)sf->data;
    344:   MPI_Comm            comm;
    345:   PetscMPIInt         size, rank;

    347:   PetscFunctionBegin;
    348:   /* Lazily construct these large arrays if users really need them for this type of SF. Very likely, they do not */
    349:   PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
    350:   PetscCallMPI(MPI_Comm_size(comm, &size));
    351:   PetscCallMPI(MPI_Comm_rank(comm, &rank));
    352:   if (niranks) *niranks = size;

    354:   /* PetscSF_Basic has distinguished incoming ranks. Here we do not need that. But we must put self as the first and
    355:      sort other ranks. See comments in PetscSFSetUp_Basic about MatGetBrowsOfAoCols_MPIAIJ on why.
    356:    */
    357:   if (iranks) {
    358:     if (!dat->iranks) {
    359:       PetscCall(PetscMalloc1(size, &dat->iranks));
    360:       dat->iranks[0] = rank;
    361:       for (PetscMPIInt i = 0, j = 1; i < size; i++) {
    362:         if (i == rank) continue;
    363:         dat->iranks[j++] = i;
    364:       }
    365:     }
    366:     *iranks = dat->iranks; /* dat->iranks was init'ed to NULL by PetscNew */
    367:   }

    369:   if (ioffset) {
    370:     if (!dat->ioffset) {
    371:       PetscCall(PetscMalloc1(size + 1, &dat->ioffset));
    372:       for (PetscMPIInt i = 0; i <= size; i++) dat->ioffset[i] = i * sf->nroots;
    373:     }
    374:     *ioffset = dat->ioffset;
    375:   }

    377:   if (irootloc) {
    378:     if (!dat->irootloc) {
    379:       PetscCall(PetscMalloc1(sf->nleaves, &dat->irootloc));
    380:       for (PetscMPIInt i = 0; i < size; i++) {
    381:         for (PetscInt j = 0; j < sf->nroots; j++) dat->irootloc[i * sf->nroots + j] = j;
    382:       }
    383:     }
    384:     *irootloc = dat->irootloc;
    385:   }
    386:   PetscFunctionReturn(PETSC_SUCCESS);
    387: }

    389: PETSC_INTERN PetscErrorCode PetscSFCreateLocalSF_Allgatherv(PetscSF sf, PetscSF *out)
    390: {
    391:   PetscInt     i, nroots, nleaves, rstart, *ilocal;
    392:   PetscSFNode *iremote;
    393:   PetscSF      lsf;

    395:   PetscFunctionBegin;
    396:   nleaves = sf->nleaves ? sf->nroots : 0; /* sf->nleaves can be zero with SFGather(v) */
    397:   nroots  = nleaves;
    398:   PetscCall(PetscMalloc1(nleaves, &ilocal));
    399:   PetscCall(PetscMalloc1(nleaves, &iremote));
    400:   PetscCall(PetscLayoutGetRange(sf->map, &rstart, NULL));

    402:   for (i = 0; i < nleaves; i++) {
    403:     ilocal[i]        = rstart + i; /* lsf does not change leave indices */
    404:     iremote[i].rank  = 0;          /* rank in PETSC_COMM_SELF */
    405:     iremote[i].index = i;          /* root index */
    406:   }

    408:   PetscCall(PetscSFCreate(PETSC_COMM_SELF, &lsf));
    409:   PetscCall(PetscSFSetGraph(lsf, nroots, nleaves, ilocal, PETSC_OWN_POINTER, iremote, PETSC_OWN_POINTER));
    410:   PetscCall(PetscSFSetUp(lsf));
    411:   *out = lsf;
    412:   PetscFunctionReturn(PETSC_SUCCESS);
    413: }

    415: PETSC_INTERN PetscErrorCode PetscSFCreate_Allgatherv(PetscSF sf)
    416: {
    417:   PetscSF_Allgatherv *dat = (PetscSF_Allgatherv *)sf->data;

    419:   PetscFunctionBegin;
    420:   sf->ops->BcastEnd  = PetscSFBcastEnd_Basic;
    421:   sf->ops->ReduceEnd = PetscSFReduceEnd_Allgatherv;

    423:   sf->ops->SetUp           = PetscSFSetUp_Allgatherv;
    424:   sf->ops->Reset           = PetscSFReset_Allgatherv;
    425:   sf->ops->Destroy         = PetscSFDestroy_Allgatherv;
    426:   sf->ops->GetRootRanks    = PetscSFGetRootRanks_Allgatherv;
    427:   sf->ops->GetLeafRanks    = PetscSFGetLeafRanks_Allgatherv;
    428:   sf->ops->GetGraph        = PetscSFGetGraph_Allgatherv;
    429:   sf->ops->BcastBegin      = PetscSFBcastBegin_Allgatherv;
    430:   sf->ops->ReduceBegin     = PetscSFReduceBegin_Allgatherv;
    431:   sf->ops->FetchAndOpBegin = PetscSFFetchAndOpBegin_Allgatherv;
    432:   sf->ops->FetchAndOpEnd   = PetscSFFetchAndOpEnd_Allgatherv;
    433:   sf->ops->CreateLocalSF   = PetscSFCreateLocalSF_Allgatherv;
    434:   sf->ops->BcastToZero     = PetscSFBcastToZero_Allgatherv;

    436:   sf->collective = PETSC_TRUE;

    438:   PetscCall(PetscNew(&dat));
    439:   dat->bcast_root = -1;
    440:   sf->data        = (void *)dat;
    441:   PetscFunctionReturn(PETSC_SUCCESS);
    442: }