sys/objects/subcomm.c

/*
     Provides utility routines for split MPI communicator.
*/
#include <petscsys.h> /*I   "petscsys.h"    I*/
#include <petscviewer.h>

const char *const PetscSubcommTypes[] = {"GENERAL", "CONTIGUOUS", "INTERLACED", "PetscSubcommType", "PETSC_SUBCOMM_", NULL};

static PetscErrorCode PetscSubcommCreate_contiguous(PetscSubcomm);
static PetscErrorCode PetscSubcommCreate_interlaced(PetscSubcomm);

/*@
  PetscSubcommSetFromOptions - Allows setting options for a `PetscSubcomm`

  Collective

  Input Parameter:
. psubcomm - `PetscSubcomm` context

  Level: beginner

.seealso: `PetscSubcomm`, `PetscSubcommCreate()`
@*/
PetscErrorCode PetscSubcommSetFromOptions(PetscSubcomm psubcomm)
{
  PetscSubcommType type;
  PetscBool        flg;

  PetscFunctionBegin;
  PetscCheck(psubcomm, PETSC_COMM_SELF, PETSC_ERR_ARG_NULL, "Must call PetscSubcommCreate first");

  PetscOptionsBegin(psubcomm->parent, psubcomm->subcommprefix, "Options for PetscSubcomm", NULL);
  PetscCall(PetscOptionsEnum("-psubcomm_type", NULL, NULL, PetscSubcommTypes, (PetscEnum)psubcomm->type, (PetscEnum *)&type, &flg));
  if (flg && psubcomm->type != type) {
    /* free old structures */
    PetscCall(PetscCommDestroy(&(psubcomm)->dupparent));
    PetscCall(PetscCommDestroy(&(psubcomm)->child));
    PetscCall(PetscFree((psubcomm)->subsize));
    switch (type) {
    case PETSC_SUBCOMM_GENERAL:
      SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "Runtime option PETSC_SUBCOMM_GENERAL is not supported, use PetscSubcommSetTypeGeneral()");
    case PETSC_SUBCOMM_CONTIGUOUS:
      PetscCall(PetscSubcommCreate_contiguous(psubcomm));
      break;
    case PETSC_SUBCOMM_INTERLACED:
      PetscCall(PetscSubcommCreate_interlaced(psubcomm));
      break;
    default:
      SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "PetscSubcommType %s is not supported yet", PetscSubcommTypes[type]);
    }
  }

  PetscCall(PetscOptionsName("-psubcomm_view", "Triggers display of PetscSubcomm context", "PetscSubcommView", &flg));
  if (flg) PetscCall(PetscSubcommView(psubcomm, PETSC_VIEWER_STDOUT_(psubcomm->parent)));
  PetscOptionsEnd();
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@
  PetscSubcommSetOptionsPrefix - Sets the prefix used for searching for options in the options database for this object

  Logically Collective

  Level: intermediate

  Input Parameters:
+ psubcomm - `PetscSubcomm` context
- pre      - the prefix to prepend all `PetscSubcomm` item names with.

.seealso: `PetscSubcomm`, `PetscSubcommCreate()`
@*/
PetscErrorCode PetscSubcommSetOptionsPrefix(PetscSubcomm psubcomm, const char pre[])
{
  PetscFunctionBegin;
  if (!pre) {
    PetscCall(PetscFree(psubcomm->subcommprefix));
  } else {
    PetscCheck(pre[0] != '-', PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Options prefix should not begin with a hyphen");
    PetscCall(PetscFree(psubcomm->subcommprefix));
    PetscCall(PetscStrallocpy(pre, &psubcomm->subcommprefix));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@
  PetscSubcommView - Views a `PetscSubcomm`

  Collective

  Input Parameters:
+ psubcomm - `PetscSubcomm` context
- viewer   - `PetscViewer` to display the information

  Level: beginner

.seealso: `PetscSubcomm`, `PetscSubcommCreate()`, `PetscViewer`
@*/
PetscErrorCode PetscSubcommView(PetscSubcomm psubcomm, PetscViewer viewer)
{
  PetscBool         isascii;
  PetscViewerFormat format;

  PetscFunctionBegin;
  PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
  PetscCheck(isascii, PETSC_COMM_SELF, PETSC_ERR_SUP, "Not supported yet");
  PetscCall(PetscViewerGetFormat(viewer, &format));
  if (format == PETSC_VIEWER_DEFAULT) {
    MPI_Comm    comm = psubcomm->parent;
    PetscMPIInt rank, size, subsize, subrank, duprank;

    PetscCallMPI(MPI_Comm_size(comm, &size));
    PetscCall(PetscViewerASCIIPrintf(viewer, "PetscSubcomm type %s with total %d MPI processes:\n", PetscSubcommTypes[psubcomm->type], size));
    PetscCallMPI(MPI_Comm_rank(comm, &rank));
    PetscCallMPI(MPI_Comm_size(psubcomm->child, &subsize));
    PetscCallMPI(MPI_Comm_rank(psubcomm->child, &subrank));
    PetscCallMPI(MPI_Comm_rank(psubcomm->dupparent, &duprank));
    PetscCall(PetscViewerASCIIPushSynchronized(viewer));
    PetscCall(PetscViewerASCIISynchronizedPrintf(viewer, "  [%d], color %d, sub-size %d, sub-rank %d, duprank %d\n", rank, psubcomm->color, subsize, subrank, duprank));
    PetscCall(PetscViewerFlush(viewer));
    PetscCall(PetscViewerASCIIPopSynchronized(viewer));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@
  PetscSubcommSetNumber - Set total number of subcommunicators desired in the given `PetscSubcomm`

  Collective

  Input Parameters:
+ psubcomm - `PetscSubcomm` context
- nsubcomm - the total number of subcommunicators in psubcomm

  Level: advanced

.seealso: `PetscSubcomm`, `PetscSubcommCreate()`, `PetscSubcommDestroy()`, `PetscSubcommSetType()`, `PetscSubcommSetTypeGeneral()`
@*/
PetscErrorCode PetscSubcommSetNumber(PetscSubcomm psubcomm, PetscInt nsubcomm)
{
  MPI_Comm    comm = psubcomm->parent;
  PetscMPIInt msub, size;

  PetscFunctionBegin;
  PetscCheck(psubcomm, PETSC_COMM_SELF, PETSC_ERR_ARG_NULL, "PetscSubcomm is not created. Call PetscSubcommCreate() first");
  PetscCallMPI(MPI_Comm_size(comm, &size));
  PetscCall(PetscMPIIntCast(nsubcomm, &msub));
  PetscCheck(msub >= 1 && msub <= size, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Num of subcommunicators %d cannot be < 1 or > input comm size %d", msub, size);

  psubcomm->n = msub;
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@
  PetscSubcommSetType - Set the way the original MPI communicator is divided up in the `PetscSubcomm`

  Collective

  Input Parameters:
+ psubcomm    - `PetscSubcomm` context
- subcommtype - `PetscSubcommType` `PETSC_SUBCOMM_CONTIGUOUS` or `PETSC_SUBCOMM_INTERLACED`

  Level: advanced

.seealso: `PetscSubcommType`, `PETSC_SUBCOMM_CONTIGUOUS`, `PETSC_SUBCOMM_INTERLACED`,
          `PetscSubcommCreate()`, `PetscSubcommDestroy()`, `PetscSubcommSetNumber()`, `PetscSubcommSetTypeGeneral()`
@*/
PetscErrorCode PetscSubcommSetType(PetscSubcomm psubcomm, PetscSubcommType subcommtype)
{
  PetscFunctionBegin;
  PetscCheck(psubcomm, PETSC_COMM_SELF, PETSC_ERR_ARG_NULL, "PetscSubcomm is not created. Call PetscSubcommCreate()");
  PetscCheck(psubcomm->n >= 1, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "number of subcommunicators %d is incorrect. Call PetscSubcommSetNumber()", psubcomm->n);

  if (subcommtype == PETSC_SUBCOMM_CONTIGUOUS) {
    PetscCall(PetscSubcommCreate_contiguous(psubcomm));
  } else if (subcommtype == PETSC_SUBCOMM_INTERLACED) {
    PetscCall(PetscSubcommCreate_interlaced(psubcomm));
  } else SETERRQ(psubcomm->parent, PETSC_ERR_SUP, "PetscSubcommType %s is not supported yet", PetscSubcommTypes[subcommtype]);
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@
  PetscSubcommSetTypeGeneral - Divides up a communicator based on a specific user's specification

  Collective

  Input Parameters:
+ psubcomm - `PetscSubcomm` context
. color    - control of subset assignment (nonnegative integer). Processes with the same color are in the same subcommunicator.
- subrank  - rank in the subcommunicator

  Level: advanced

.seealso: `PetscSubcommType`, `PETSC_SUBCOMM_CONTIGUOUS`, `PETSC_SUBCOMM_INTERLACED`, `PetscSubcommCreate()`, `PetscSubcommDestroy()`, `PetscSubcommSetNumber()`, `PetscSubcommSetType()`
@*/
PetscErrorCode PetscSubcommSetTypeGeneral(PetscSubcomm psubcomm, PetscMPIInt color, PetscMPIInt subrank)
{
  MPI_Comm    subcomm = 0, dupcomm = 0, comm = psubcomm->parent;
  PetscMPIInt size, icolor, duprank, *recvbuf, sendbuf[3], mysubsize, rank, *subsize;
  PetscMPIInt i, nsubcomm = psubcomm->n;

  PetscFunctionBegin;
  PetscCheck(psubcomm, PETSC_COMM_SELF, PETSC_ERR_ARG_NULL, "PetscSubcomm is not created. Call PetscSubcommCreate()");
  PetscCheck(nsubcomm >= 1, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "number of subcommunicators %d is incorrect. Call PetscSubcommSetNumber()", nsubcomm);

  PetscCallMPI(MPI_Comm_split(comm, color, subrank, &subcomm));

  /* create dupcomm with same size as comm, but its rank, duprank, maps subcomm's contiguously into dupcomm */
  /* TODO: this can be done in an ostensibly scalale way (i.e., without allocating an array of size 'size') as is done in PetscObjectsCreateGlobalOrdering(). */
  PetscCallMPI(MPI_Comm_size(comm, &size));
  PetscCall(PetscMalloc1(2 * size, &recvbuf));

  PetscCallMPI(MPI_Comm_rank(comm, &rank));
  PetscCallMPI(MPI_Comm_size(subcomm, &mysubsize));

  sendbuf[0] = color;
  sendbuf[1] = mysubsize;
  PetscCallMPI(MPI_Allgather(sendbuf, 2, MPI_INT, recvbuf, 2, MPI_INT, comm));

  PetscCall(PetscCalloc1(nsubcomm, &subsize));
  for (i = 0; i < 2 * size; i += 2) subsize[recvbuf[i]] = recvbuf[i + 1];
  PetscCall(PetscFree(recvbuf));

  duprank = 0;
  for (icolor = 0; icolor < nsubcomm; icolor++) {
    if (icolor != color) { /* not color of this process */
      duprank += subsize[icolor];
    } else {
      duprank += subrank;
      break;
    }
  }
  PetscCallMPI(MPI_Comm_split(comm, 0, duprank, &dupcomm));

  PetscCall(PetscCommDuplicate(dupcomm, &psubcomm->dupparent, NULL));
  PetscCall(PetscCommDuplicate(subcomm, &psubcomm->child, NULL));
  PetscCallMPI(MPI_Comm_free(&dupcomm));
  PetscCallMPI(MPI_Comm_free(&subcomm));

  psubcomm->color   = color;
  psubcomm->subsize = subsize;
  psubcomm->type    = PETSC_SUBCOMM_GENERAL;
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@
  PetscSubcommDestroy - Destroys a `PetscSubcomm` object

  Collective

  Input Parameter:
. psubcomm - the `PetscSubcomm` context

  Level: advanced

.seealso: `PetscSubcommCreate()`, `PetscSubcommSetType()`
@*/
PetscErrorCode PetscSubcommDestroy(PetscSubcomm *psubcomm)
{
  PetscFunctionBegin;
  if (!*psubcomm) PetscFunctionReturn(PETSC_SUCCESS);
  PetscCall(PetscCommDestroy(&(*psubcomm)->dupparent));
  PetscCall(PetscCommDestroy(&(*psubcomm)->child));
  PetscCall(PetscFree((*psubcomm)->subsize));
  if ((*psubcomm)->subcommprefix) PetscCall(PetscFree((*psubcomm)->subcommprefix));
  PetscCall(PetscFree(*psubcomm));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@
  PetscSubcommCreate - Create a `PetscSubcomm` context. This object is used to manage the division of a `MPI_Comm` into subcommunicators

  Collective

  Input Parameter:
. comm - MPI communicator

  Output Parameter:
. psubcomm - location to store the `PetscSubcomm` context

  Level: advanced

.seealso: `PetscSubcomm`, `PetscSubcommDestroy()`, `PetscSubcommSetTypeGeneral()`, `PetscSubcommSetFromOptions()`, `PetscSubcommSetType()`,
          `PetscSubcommSetNumber()`
@*/
PetscErrorCode PetscSubcommCreate(MPI_Comm comm, PetscSubcomm *psubcomm)
{
  PetscMPIInt rank, size;

  PetscFunctionBegin;
  PetscCall(PetscNew(psubcomm));

  /* set defaults */
  PetscCallMPI(MPI_Comm_rank(comm, &rank));
  PetscCallMPI(MPI_Comm_size(comm, &size));

  (*psubcomm)->parent    = comm;
  (*psubcomm)->dupparent = comm;
  (*psubcomm)->child     = PETSC_COMM_SELF;
  (*psubcomm)->n         = size;
  (*psubcomm)->color     = rank;
  (*psubcomm)->subsize   = NULL;
  (*psubcomm)->type      = PETSC_SUBCOMM_INTERLACED;
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*@C
  PetscSubcommGetParent - Gets the communicator that was used to create the `PetscSubcomm`

  Collective

  Input Parameter:
. scomm - the `PetscSubcomm`

  Output Parameter:
. pcomm - location to store the parent communicator

  Level: intermediate

.seealso: `PetscSubcommDestroy()`, `PetscSubcommSetTypeGeneral()`, `PetscSubcommSetFromOptions()`, `PetscSubcommSetType()`,
          `PetscSubcommSetNumber()`, `PetscSubcommGetChild()`, `PetscSubcommContiguousParent()`
@*/
PetscErrorCode PetscSubcommGetParent(PetscSubcomm scomm, MPI_Comm *pcomm)
{
  *pcomm = PetscSubcommParent(scomm);
  return PETSC_SUCCESS;
}

/*@C
  PetscSubcommGetContiguousParent - Gets a communicator that is a duplicate of the parent but has the ranks
  reordered by the order they are in the children

  Collective

  Input Parameter:
. scomm - the `PetscSubcomm`

  Output Parameter:
. pcomm - location to store the parent communicator

  Level: intermediate

.seealso: `PetscSubcommDestroy()`, `PetscSubcommSetTypeGeneral()`, `PetscSubcommSetFromOptions()`, `PetscSubcommSetType()`,
          `PetscSubcommSetNumber()`, `PetscSubcommGetChild()`, `PetscSubcommContiguousParent()`
@*/
PetscErrorCode PetscSubcommGetContiguousParent(PetscSubcomm scomm, MPI_Comm *pcomm)
{
  *pcomm = PetscSubcommContiguousParent(scomm);
  return PETSC_SUCCESS;
}

/*@C
  PetscSubcommGetChild - Gets the communicator created by the `PetscSubcomm`. This is part of one of the subcommunicators created by the `PetscSubcomm`

  Collective

  Input Parameter:
. scomm - the `PetscSubcomm`

  Output Parameter:
. ccomm - location to store the child communicator

  Level: intermediate

.seealso: `PetscSubcommDestroy()`, `PetscSubcommSetTypeGeneral()`, `PetscSubcommSetFromOptions()`, `PetscSubcommSetType()`,
          `PetscSubcommSetNumber()`, `PetscSubcommGetParent()`, `PetscSubcommContiguousParent()`
@*/
PetscErrorCode PetscSubcommGetChild(PetscSubcomm scomm, MPI_Comm *ccomm)
{
  *ccomm = PetscSubcommChild(scomm);
  return PETSC_SUCCESS;
}

static PetscErrorCode PetscSubcommCreate_contiguous(PetscSubcomm psubcomm)
{
  PetscMPIInt rank, size, *subsize, duprank = -1, subrank = -1;
  PetscMPIInt np_subcomm, nleftover, i, color = -1, rankstart, nsubcomm = psubcomm->n;
  MPI_Comm    subcomm = 0, dupcomm = 0, comm = psubcomm->parent;

  PetscFunctionBegin;
  PetscCallMPI(MPI_Comm_rank(comm, &rank));
  PetscCallMPI(MPI_Comm_size(comm, &size));

  /* get size of each subcommunicator */
  PetscCall(PetscMalloc1(1 + nsubcomm, &subsize));

  np_subcomm = size / nsubcomm;
  nleftover  = size - nsubcomm * np_subcomm;
  for (i = 0; i < nsubcomm; i++) {
    subsize[i] = np_subcomm;
    if (i < nleftover) subsize[i]++;
  }

  /* get color and subrank of this proc */
  rankstart = 0;
  for (i = 0; i < nsubcomm; i++) {
    if (rank >= rankstart && rank < rankstart + subsize[i]) {
      color   = i;
      subrank = rank - rankstart;
      duprank = rank;
      break;
    } else rankstart += subsize[i];
  }

  PetscCallMPI(MPI_Comm_split(comm, color, subrank, &subcomm));

  /* create dupcomm with same size as comm, but its rank, duprank, maps subcomm's contiguously into dupcomm */
  PetscCallMPI(MPI_Comm_split(comm, 0, duprank, &dupcomm));
  PetscCall(PetscCommDuplicate(dupcomm, &psubcomm->dupparent, NULL));
  PetscCall(PetscCommDuplicate(subcomm, &psubcomm->child, NULL));
  PetscCallMPI(MPI_Comm_free(&dupcomm));
  PetscCallMPI(MPI_Comm_free(&subcomm));

  psubcomm->color   = color;
  psubcomm->subsize = subsize;
  psubcomm->type    = PETSC_SUBCOMM_CONTIGUOUS;
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*
   Note:
   In PCREDUNDANT, to avoid data scattering from subcomm back to original comm, we create subcommunicators
   by iteratively taking a process into a subcommunicator.
   Example: size=4, nsubcomm=(*psubcomm)->n=3
     comm=(*psubcomm)->parent:
      rank:     [0]  [1]  [2]  [3]
      color:     0    1    2    0

     subcomm=(*psubcomm)->comm:
      subrank:  [0]  [0]  [0]  [1]

     dupcomm=(*psubcomm)->dupparent:
      duprank:  [0]  [2]  [3]  [1]

     Here, subcomm[color = 0] has subsize=2, owns process [0] and [3]
           subcomm[color = 1] has subsize=1, owns process [1]
           subcomm[color = 2] has subsize=1, owns process [2]
           dupcomm has same number of processes as comm, and its duprank maps
           processes in subcomm contiguously into a 1d array:
            duprank: [0] [1]      [2]         [3]
            rank:    [0] [3]      [1]         [2]
                    subcomm[0] subcomm[1]  subcomm[2]
*/

static PetscErrorCode PetscSubcommCreate_interlaced(PetscSubcomm psubcomm)
{
  PetscMPIInt rank, size, *subsize, duprank, subrank;
  PetscMPIInt np_subcomm, nleftover, i, j, color, nsubcomm = psubcomm->n;
  MPI_Comm    subcomm = 0, dupcomm = 0, comm = psubcomm->parent;

  PetscFunctionBegin;
  PetscCallMPI(MPI_Comm_rank(comm, &rank));
  PetscCallMPI(MPI_Comm_size(comm, &size));

  /* get size of each subcommunicator */
  PetscCall(PetscMalloc1(1 + nsubcomm, &subsize));

  np_subcomm = size / nsubcomm;
  nleftover  = size - nsubcomm * np_subcomm;
  for (i = 0; i < nsubcomm; i++) {
    subsize[i] = np_subcomm;
    if (i < nleftover) subsize[i]++;
  }

  /* find color for this proc */
  color   = rank % nsubcomm;
  subrank = rank / nsubcomm;

  PetscCallMPI(MPI_Comm_split(comm, color, subrank, &subcomm));

  j       = 0;
  duprank = 0;
  for (i = 0; i < nsubcomm; i++) {
    if (j == color) {
      duprank += subrank;
      break;
    }
    duprank += subsize[i];
    j++;
  }

  /* create dupcomm with same size as comm, but its rank, duprank, maps subcomm's contiguously into dupcomm */
  PetscCallMPI(MPI_Comm_split(comm, 0, duprank, &dupcomm));
  PetscCall(PetscCommDuplicate(dupcomm, &psubcomm->dupparent, NULL));
  PetscCall(PetscCommDuplicate(subcomm, &psubcomm->child, NULL));
  PetscCallMPI(MPI_Comm_free(&dupcomm));
  PetscCallMPI(MPI_Comm_free(&subcomm));

  psubcomm->color   = color;
  psubcomm->subsize = subsize;
  psubcomm->type    = PETSC_SUBCOMM_INTERLACED;
  PetscFunctionReturn(PETSC_SUCCESS);
}