xref: /petsc/src/sys/utils/psplit.c (revision 08401ef684002a709c6d3db98a0c9f54a8bcf1ec)

#include <petscsys.h>           /*I    "petscsys.h" I*/

/*@
    PetscSplitOwnershipBlock - Given a global (or local) length determines a local
        (or global) length via a simple formula. Splits so each processors local size
        is divisible by the block size.

   Collective (if N is PETSC_DECIDE)

   Input Parameters:
+    comm - MPI communicator that shares the object being divided
.    bs - block size
.    n - local length (or PETSC_DECIDE to have it set)
-    N - global length (or PETSC_DECIDE)

  Level: developer

   Notes:
     n and N cannot be both PETSC_DECIDE

     If one processor calls this with N of PETSC_DECIDE then all processors
     must, otherwise the program will hang.

.seealso: PetscSplitOwnership()

@*/
PetscErrorCode  PetscSplitOwnershipBlock(MPI_Comm comm,PetscInt bs,PetscInt *n,PetscInt *N)
{
  PetscMPIInt    size,rank;

  PetscFunctionBegin;
  PetscCheckFalse(*N == PETSC_DECIDE && *n == PETSC_DECIDE,PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Both n and N cannot be PETSC_DECIDE");

  if (*N == PETSC_DECIDE) {
    PetscCheck(*n % bs == 0,PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"local size %" PetscInt_FMT " not divisible by block size %" PetscInt_FMT,*n,bs);
    PetscCall(MPIU_Allreduce(n,N,1,MPIU_INT,MPI_SUM,comm));
  } else if (*n == PETSC_DECIDE) {
    PetscInt Nbs = *N/bs;
    PetscCallMPI(MPI_Comm_size(comm,&size));
    PetscCallMPI(MPI_Comm_rank(comm,&rank));
    *n   = bs*(Nbs/size + ((Nbs % size) > rank));
  }
  PetscFunctionReturn(0);
}

/*@
    PetscSplitOwnership - Given a global (or local) length determines a local
        (or global) length via a simple formula

   Collective (if n or N is PETSC_DECIDE)

   Input Parameters:
+    comm - MPI communicator that shares the object being divided
.    n - local length (or PETSC_DECIDE to have it set)
-    N - global length (or PETSC_DECIDE)

  Level: developer

   Notes:
     n and N cannot be both PETSC_DECIDE

     If one processor calls this with n or N of PETSC_DECIDE then all processors
     must. Otherwise, an error is thrown in debug mode while the program will hang
     in optimized (i.e. configured --with-debugging=0) mode.

.seealso: PetscSplitOwnershipBlock()

@*/
PetscErrorCode  PetscSplitOwnership(MPI_Comm comm,PetscInt *n,PetscInt *N)
{
  PetscMPIInt    size,rank;

  PetscFunctionBegin;
  PetscCheckFalse(*N == PETSC_DECIDE && *n == PETSC_DECIDE,PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Both n and N cannot be PETSC_DECIDE\n  likely a call to VecSetSizes() or MatSetSizes() is wrong.\nSee https://petsc.org/release/faq/#split-ownership");
  if (PetscDefined(USE_DEBUG)) {
    PetscMPIInt l[2],g[2];
    l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
    l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
    PetscCallMPI(MPI_Comm_size(comm,&size));
    PetscCall(MPIU_Allreduce(l,g,2,MPI_INT,MPI_SUM,comm));
    PetscCheckFalse(g[0] && g[0] != size,comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for local size");
    PetscCheckFalse(g[1] && g[1] != size,comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for global size");
  }

  if (*N == PETSC_DECIDE) {
    PetscInt64 m = *n, M;
    PetscCall(MPIU_Allreduce(&m,&M,1,MPIU_INT64,MPI_SUM,comm));
    PetscCheck(M <= PETSC_MAX_INT,comm,PETSC_ERR_INT_OVERFLOW,"Global size overflow %" PetscInt64_FMT ". You may consider ./configure PETSc with --with-64-bit-indices for the case you are running", M);
    else *N = (PetscInt)M;
  } else if (*n == PETSC_DECIDE) {
    PetscCallMPI(MPI_Comm_size(comm,&size));
    PetscCallMPI(MPI_Comm_rank(comm,&rank));
    *n   = *N/size + ((*N % size) > rank);
  } else if (PetscDefined(USE_DEBUG)) {
    PetscInt tmp;
    PetscCall(MPIU_Allreduce(n,&tmp,1,MPIU_INT,MPI_SUM,comm));
    PetscCheck(tmp == *N,PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Sum of local lengths %" PetscInt_FMT " does not equal global length %" PetscInt_FMT ", my local length %" PetscInt_FMT "\n  likely a call to VecSetSizes() or MatSetSizes() is wrong.\nSee https://petsc.org/release/faq/#split-ownership",tmp,*N,*n);
  }
  PetscFunctionReturn(0);
}

/*@
    PetscSplitOwnershipEqual - Given a global (or local) length determines a local
        (or global) length via a simple formula, trying to have all local lengths equal

   Collective (if n or N is PETSC_DECIDE)

   Input Parameters:
+    comm - MPI communicator that shares the object being divided
.    n - local length (or PETSC_DECIDE to have it set)
-    N - global length (or PETSC_DECIDE)

   Level: developer

   Notes:
     This is intended to be used with MATSCALAPACK, where the local size must
     be equal in all processes (except possibly the last one). For instance,
     the local sizes when spliting N=50 with 6 processes are 9,9,9,9,9,5

     n and N cannot be both PETSC_DECIDE

     If one processor calls this with n or N of PETSC_DECIDE then all processors
     must. Otherwise, an error is thrown in debug mode while the program will hang
     in optimized (i.e. configured --with-debugging=0) mode.

.seealso: PetscSplitOwnership(), PetscSplitOwnershipBlock()

@*/
PetscErrorCode  PetscSplitOwnershipEqual(MPI_Comm comm,PetscInt *n,PetscInt *N)
{
  PetscMPIInt    size,rank;

  PetscFunctionBegin;
  PetscCheckFalse(*N == PETSC_DECIDE && *n == PETSC_DECIDE,PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Both n and N cannot be PETSC_DECIDE");
  if (PetscDefined(USE_DEBUG)) {
    PetscMPIInt l[2],g[2];
    l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
    l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
    PetscCallMPI(MPI_Comm_size(comm,&size));
    PetscCall(MPIU_Allreduce(l,g,2,MPI_INT,MPI_SUM,comm));
    PetscCheckFalse(g[0] && g[0] != size,comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for local size");
    PetscCheckFalse(g[1] && g[1] != size,comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for global size");
  }

  if (*N == PETSC_DECIDE) {
    PetscInt64 m = *n, M;
    PetscCall(MPIU_Allreduce(&m,&M,1,MPIU_INT64,MPI_SUM,comm));
    PetscCheck(M <= PETSC_MAX_INT,comm,PETSC_ERR_INT_OVERFLOW,"Global size overflow %" PetscInt64_FMT ". You may consider ./configure PETSc with --with-64-bit-indices for the case you are running", M);
    else *N = (PetscInt)M;
  } else if (*n == PETSC_DECIDE) {
    PetscCallMPI(MPI_Comm_size(comm,&size));
    PetscCallMPI(MPI_Comm_rank(comm,&rank));
    *n = *N/size;
    if (*N % size) {
      if ((rank+1)*(*n+1)<=*N)  *n = *n+1;
      else if (rank*(*n+1)<=*N) *n = *N-rank*(*n+1);
      else *n = 0;
    }
  } else if (PetscDefined(USE_DEBUG)) {
    PetscInt tmp;
    PetscCall(MPIU_Allreduce(n,&tmp,1,MPIU_INT,MPI_SUM,comm));
    PetscCheck(tmp == *N,PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Sum of local lengths %" PetscInt_FMT " does not equal global length %" PetscInt_FMT ", my local length %" PetscInt_FMT,tmp,*N,*n);
  }
  PetscFunctionReturn(0);
}