xref: /petsc/src/vec/is/sf/impls/basic/alltoall/sfalltoall.c (revision 646b835dd74e42d2b8324facdc6838bbab01abab)

#include <../src/vec/is/sf/impls/basic/allgatherv/sfallgatherv.h>
#include <../src/vec/is/sf/impls/basic/allgather/sfallgather.h>
#include <../src/vec/is/sf/impls/basic/gatherv/sfgatherv.h>

/* Reuse the type. The difference is some fields (i.e., displs, recvcounts) are not used, which is not a big deal */
typedef PetscSF_Allgatherv PetscSF_Alltoall;

static PetscErrorCode PetscSFLinkStartCommunication_Alltoall(PetscSF sf, PetscSFLink link, PetscSFDirection direction)
{
  MPI_Comm     comm    = MPI_COMM_NULL;
  void        *rootbuf = NULL, *leafbuf = NULL;
  MPI_Request *req  = NULL;
  MPI_Datatype unit = link->unit;

  PetscFunctionBegin;
  if (direction == PETSCSF_ROOT2LEAF) {
    PetscCall(PetscSFLinkCopyRootBufferInCaseNotUseGpuAwareMPI(sf, link, PETSC_TRUE /* device2host before sending */));
  } else {
    PetscCall(PetscSFLinkCopyLeafBufferInCaseNotUseGpuAwareMPI(sf, link, PETSC_TRUE /* device2host */));
  }
  PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
  PetscCall(PetscSFLinkGetMPIBuffersAndRequests(sf, link, direction, &rootbuf, &leafbuf, &req, NULL));
  PetscCall(PetscSFLinkSyncStreamBeforeCallMPI(sf, link));

  if (direction == PETSCSF_ROOT2LEAF) {
    PetscCallMPI(MPIU_Ialltoall(rootbuf, 1, unit, leafbuf, 1, unit, comm, req));
  } else {
    PetscCallMPI(MPIU_Ialltoall(leafbuf, 1, unit, rootbuf, 1, unit, comm, req));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscSFSetCommunicationOps_Alltoall(PetscSF sf, PetscSFLink link)
{
  PetscFunctionBegin;
  link->StartCommunication = PetscSFLinkStartCommunication_Alltoall;
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*===================================================================================*/
/*              Implementations of SF public APIs                                    */
/*===================================================================================*/
static PetscErrorCode PetscSFGetGraph_Alltoall(PetscSF sf, PetscInt *nroots, PetscInt *nleaves, const PetscInt **ilocal, const PetscSFNode **iremote)
{
  PetscInt i;

  PetscFunctionBegin;
  if (nroots) *nroots = sf->nroots;
  if (nleaves) *nleaves = sf->nleaves;
  if (ilocal) *ilocal = NULL; /* Contiguous local indices */
  if (iremote) {
    if (!sf->remote) {
      PetscCall(PetscMalloc1(sf->nleaves, &sf->remote));
      sf->remote_alloc = sf->remote;
      for (i = 0; i < sf->nleaves; i++) {
        sf->remote[i].rank  = i;
        sf->remote[i].index = i;
      }
    }
    *iremote = sf->remote;
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscSFCreateLocalSF_Alltoall(PetscSF sf, PetscSF *out)
{
  PetscInt     nroots = 1, nleaves = 1, *ilocal;
  PetscSFNode *iremote = NULL;
  PetscSF      lsf;
  PetscMPIInt  rank;

  PetscFunctionBegin;
  nroots  = 1;
  nleaves = 1;
  PetscCallMPI(MPI_Comm_rank(PetscObjectComm((PetscObject)sf), &rank));
  PetscCall(PetscMalloc1(nleaves, &ilocal));
  PetscCall(PetscMalloc1(nleaves, &iremote));
  ilocal[0]        = rank;
  iremote[0].rank  = 0;    /* rank in PETSC_COMM_SELF */
  iremote[0].index = rank; /* LocalSF is an embedded SF. Indices are not remapped */

  PetscCall(PetscSFCreate(PETSC_COMM_SELF, &lsf));
  PetscCall(PetscSFSetGraph(lsf, nroots, nleaves, NULL /*contiguous leaves*/, PETSC_OWN_POINTER, iremote, PETSC_OWN_POINTER));
  PetscCall(PetscSFSetUp(lsf));
  *out = lsf;
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscSFCreateEmbeddedRootSF_Alltoall(PetscSF sf, PetscInt nselected, const PetscInt *selected, PetscSF *newsf)
{
  PetscInt       i, *tmproots, *ilocal, ndranks, ndiranks;
  PetscSFNode   *iremote;
  PetscMPIInt    nroots, *roots, nleaves, *leaves, rank;
  MPI_Comm       comm;
  PetscSF_Basic *bas;
  PetscSF        esf;

  PetscFunctionBegin;
  PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
  PetscCallMPI(MPI_Comm_rank(comm, &rank));

  /* Uniq selected[] and store the result in roots[] */
  PetscCall(PetscMalloc1(nselected, &tmproots));
  PetscCall(PetscArraycpy(tmproots, selected, nselected));
  PetscCall(PetscSortRemoveDupsInt(&nselected, tmproots)); /* nselected might be changed */
  PetscCheck(tmproots[0] >= 0 && tmproots[nselected - 1] < sf->nroots, comm, PETSC_ERR_ARG_OUTOFRANGE, "Min/Max root indices %" PetscInt_FMT "/%" PetscInt_FMT " are not in [0,%" PetscInt_FMT ")", tmproots[0], tmproots[nselected - 1], sf->nroots);
  nroots = nselected; /* For Alltoall, we know root indices will not overflow MPI_INT */
  PetscCall(PetscMalloc1(nselected, &roots));
  for (i = 0; i < nselected; i++) roots[i] = tmproots[i];
  PetscCall(PetscFree(tmproots));

  /* Find out which leaves are still connected to roots in the embedded sf. Expect PetscCommBuildTwoSided is more scalable than MPI_Alltoall */
  PetscCall(PetscCommBuildTwoSided(comm, 0 /*empty msg*/, MPI_INT /*fake*/, nroots, roots, NULL /*todata*/, &nleaves, &leaves, NULL /*fromdata*/));

  /* Move myself ahead if rank is in leaves[], since I am a distinguished rank */
  ndranks = 0;
  for (i = 0; i < nleaves; i++) {
    if (leaves[i] == rank) {
      leaves[i] = -rank;
      ndranks   = 1;
      break;
    }
  }
  PetscCall(PetscSortMPIInt(nleaves, leaves));
  if (nleaves && leaves[0] < 0) leaves[0] = rank;

  /* Build esf and fill its fields manually (without calling PetscSFSetUp) */
  PetscCall(PetscMalloc1(nleaves, &ilocal));
  PetscCall(PetscMalloc1(nleaves, &iremote));
  for (i = 0; i < nleaves; i++) { /* 1:1 map from roots to leaves */
    ilocal[i]        = leaves[i];
    iremote[i].rank  = leaves[i];
    iremote[i].index = leaves[i];
  }
  PetscCall(PetscSFCreate(comm, &esf));
  PetscCall(PetscSFSetType(esf, PETSCSFBASIC)); /* This optimized routine can only create a basic sf */
  PetscCall(PetscSFSetGraph(esf, sf->nleaves, nleaves, ilocal, PETSC_OWN_POINTER, iremote, PETSC_OWN_POINTER));

  /* As if we are calling PetscSFSetUpRanks(esf,self's group) */
  PetscCall(PetscMalloc4(nleaves, &esf->ranks, nleaves + 1, &esf->roffset, nleaves, &esf->rmine, nleaves, &esf->rremote));
  esf->nranks     = nleaves;
  esf->ndranks    = ndranks;
  esf->roffset[0] = 0;
  for (i = 0; i < nleaves; i++) {
    esf->ranks[i]       = leaves[i];
    esf->roffset[i + 1] = i + 1;
    esf->rmine[i]       = leaves[i];
    esf->rremote[i]     = leaves[i];
  }

  /* Set up esf->data, the incoming communication (i.e., recv info), which is usually done by PetscSFSetUp_Basic */
  bas = (PetscSF_Basic *)esf->data;
  PetscCall(PetscMalloc2(nroots, &bas->iranks, nroots + 1, &bas->ioffset));
  PetscCall(PetscMalloc1(nroots, &bas->irootloc));
  /* Move myself ahead if rank is in roots[], since I am a distinguished irank */
  ndiranks = 0;
  for (i = 0; i < nroots; i++) {
    if (roots[i] == rank) {
      roots[i] = -rank;
      ndiranks = 1;
      break;
    }
  }
  PetscCall(PetscSortMPIInt(nroots, roots));
  if (nroots && roots[0] < 0) roots[0] = rank;

  bas->niranks    = nroots;
  bas->ndiranks   = ndiranks;
  bas->ioffset[0] = 0;
  bas->itotal     = nroots;
  for (i = 0; i < nroots; i++) {
    bas->iranks[i]      = roots[i];
    bas->ioffset[i + 1] = i + 1;
    bas->irootloc[i]    = roots[i];
  }

  /* See PetscSFCreateEmbeddedRootSF_Basic */
  esf->nleafreqs  = esf->nranks - esf->ndranks;
  bas->nrootreqs  = bas->niranks - bas->ndiranks;
  esf->persistent = PETSC_TRUE;
  /* Setup packing related fields */
  PetscCall(PetscSFSetUpPackFields(esf));

  esf->setupcalled = PETSC_TRUE; /* We have done setup ourselves! */
  *newsf           = esf;
  PetscFunctionReturn(PETSC_SUCCESS);
}

PETSC_INTERN PetscErrorCode PetscSFCreate_Alltoall(PetscSF sf)
{
  PetscSF_Alltoall *dat = (PetscSF_Alltoall *)sf->data;

  PetscFunctionBegin;
  sf->ops->BcastBegin  = PetscSFBcastBegin_Basic;
  sf->ops->BcastEnd    = PetscSFBcastEnd_Basic;
  sf->ops->ReduceBegin = PetscSFReduceBegin_Basic;
  sf->ops->ReduceEnd   = PetscSFReduceEnd_Basic;

  /* Inherit from Allgatherv. It is astonishing Alltoall can inherit so much from Allgather(v) */
  sf->ops->Destroy       = PetscSFDestroy_Allgatherv;
  sf->ops->Reset         = PetscSFReset_Allgatherv;
  sf->ops->FetchAndOpEnd = PetscSFFetchAndOpEnd_Allgatherv;
  sf->ops->GetRootRanks  = PetscSFGetRootRanks_Allgatherv;

  /* Inherit from Allgather. Every process gathers equal-sized data from others, which enables this inheritance. */
  sf->ops->GetLeafRanks = PetscSFGetLeafRanks_Allgatherv;
  sf->ops->SetUp        = PetscSFSetUp_Allgather;

  /* Inherit from Gatherv. Each root has only one leaf connected, which enables this inheritance */
  sf->ops->FetchAndOpBegin = PetscSFFetchAndOpBegin_Gatherv;

  /* Alltoall stuff */
  sf->ops->GetGraph             = PetscSFGetGraph_Alltoall;
  sf->ops->CreateLocalSF        = PetscSFCreateLocalSF_Alltoall;
  sf->ops->CreateEmbeddedRootSF = PetscSFCreateEmbeddedRootSF_Alltoall;

  sf->ops->SetCommunicationOps = PetscSFSetCommunicationOps_Alltoall;

  sf->collective = PETSC_TRUE;

  PetscCall(PetscNew(&dat));
  sf->data = (void *)dat;
  PetscFunctionReturn(PETSC_SUCCESS);
}