psblas3/base/internals/psi_graph_fnd_owner.F90

!   
!                Parallel Sparse BLAS  version 3.5
!      (C) Copyright 2006-2018
!        Salvatore Filippone    
!        Alfredo Buttari      
!   
!    Redistribution and use in source and binary forms, with or without
!    modification, are permitted provided that the following conditions
!    are met:
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!   
!   
!
!
! File: psi_graph_fnd_owner.f90
!
! Subroutine: psi_graph_fnd_owner
!   Figure out who owns  global indices. 
! 
! Arguments: 
!    idx(:)   - integer                 Required indices on the calling process.
!                                       
!    iprc(:)  - integer(psb_ipk_), allocatable    Output: process identifiers for the corresponding
!                                       indices
!    idxmap   - class(psb_indx_map).    The index map
!    info     - integer.                return code.
!
! This is the method to find out who owns a set of indices. 
! In principle we could do the following:
!   1. Do an allgatherv of IDX
!   2. For each of the collected indices figure if current proces owns it
!   3. Scatter the results
!   4. Loop through the answers
! This method is guaranteed to find the owner, unless an input index has
! an invalid value, however it could easily require too much additional space
! because each block of indices is replicated to all processes.
! Therefore the current routine takes a different approach:
! -1. Figure out a maximum size for a buffer to collect the IDX; the buffer
!     should allow for at least one index from each process (i.e. min size NP); also
!     check if we have an adjacency list of processes on input; 
!  0. If the initial adjacency list is not empty, use psi_adj_fnd_sweep to go
!     through all indices and use  multiple calls to psi_adjcncy_fnd_owner
!     (up to the buffer size) to see if the owning processes are in the
!     initial neighbours list;
!  1. Extract a sample from IDX, up to the buffer size, and do a call
!     to psi_a2a_fnd_owner. This is guaranteed to find the owners of all indices
!     in the sample;
!  2. Build the list of processes that own the sample indices; these are
!     (a subset of) the topological neighbours, and store the list in IDXMAP
!  3. Use psi_adj_fnd_sweep to go through all remaining indices and use
!     multiple calls to psi_adjcncy_fnd_owner (up to the buffer size)
!     to see if the owning processes are in the current neighbours list;
!  4. If the input indices IDX have not been exhausted, cycle to 1.
!
!  Thus, we are alternating between asking all processes for a subset of indices, and
!  asking a subset of processes for all the indices, thereby limiting the memory footprint to
!  a predefined maximum (that the user can force with psb_cd_set_maxspace()).
! 
subroutine psi_graph_fnd_owner(idx,iprc,idxmap,info)
  use psb_serial_mod
  use psb_const_mod
  use psb_error_mod
  use psb_penv_mod
  use psb_realloc_mod
  use psb_timers_mod
  use psb_desc_mod, psb_protect_name => psi_graph_fnd_owner
#ifdef MPI_MOD
  use mpi
#endif

  implicit none 
#ifdef MPI_H
  include 'mpif.h'
#endif
  integer(psb_lpk_), intent(in)      :: idx(:)
  integer(psb_ipk_), allocatable, intent(out) ::  iprc(:)
  class(psb_indx_map), intent(inout) :: idxmap
  integer(psb_ipk_), intent(out)     :: info


  integer(psb_lpk_), allocatable :: tidx(:)
  integer(psb_ipk_), allocatable :: tprc(:), tsmpl(:), ladj(:)  
  integer(psb_mpk_) :: icomm, minfo, iictxt
  integer(psb_ipk_) :: i,n_row,n_col,err_act,ip,j,ipnt, nsampl_out,&
       & nv, n_answers, nreqst, nsampl_in, locr_max, &
       & nreqst_max, nadj, maxspace, mxnsin
  integer(psb_lpk_) :: mglob, ih
  integer(psb_ipk_) :: ictxt,np,me, nresp
  integer(psb_ipk_), parameter :: nt=4
  integer(psb_ipk_) :: tmpv(4)
  logical, parameter  :: do_timings=.false., trace=.false., debugsz=.false.
  integer(psb_ipk_), save  :: idx_sweep0=-1, idx_loop_a2a=-1, idx_loop_neigh=-1
  real(psb_dpk_)      :: t0, t1, t2, t3, t4
  character(len=20)   :: name

  info = psb_success_
  name = 'psi_graph_fnd_owner'
  call psb_erractionsave(err_act)

  ictxt   = idxmap%get_ctxt()
  icomm   = idxmap%get_mpic()
  mglob   = idxmap%get_gr()
  n_row   = idxmap%get_lr()
  n_col   = idxmap%get_lc()
  iictxt  = ictxt 
  if ((do_timings).and.(idx_sweep0==-1))       &
       & idx_sweep0 = psb_get_timer_idx("GRPH_FND_OWN: Outer sweep")
  if ((do_timings).and.(idx_loop_a2a==-1))       &
       & idx_loop_a2a = psb_get_timer_idx("GRPH_FND_OWN: Loop a2a")
  if ((do_timings).and.(idx_loop_neigh==-1))       &
       & idx_loop_neigh = psb_get_timer_idx("GRPH_FND_OWN: Loop neigh")


  call psb_info(ictxt, me, np)

  if (np == -1) then
    info = psb_err_context_error_
    call psb_errpush(info,name)
    goto 9999
  endif

  if (.not.(idxmap%is_valid())) then 
    call psb_errpush(psb_err_from_subroutine_,name,a_err='invalid idxmap')
    goto 9999      
  end if

  !
  !
  !
  nv = size(idx)
  call psb_realloc(nv,iprc,info)
  if (info == psb_success_) call psb_realloc(nv,tidx,info)
  if (info == psb_success_) call psb_realloc(nv,tprc,info)
  if (info == psb_success_) call psb_realloc(nv,tsmpl,info)
  if (info /= psb_success_) then 
    call psb_errpush(psb_err_from_subroutine_,name,a_err='psb_realloc')
    goto 9999      
  end if
  iprc(:) = -1
  n_answers = 0
  !
  ! Start from the adjacncy list
  !
  call psb_safe_ab_cpy(idxmap%p_adjcncy,ladj,info)
  nadj = psb_size(ladj)
  ! This makes ladj allocated with size 0 just in case 
  call psb_realloc(nadj,ladj,info)
  !
  ! Throughout the subroutine, nreqst is the number of local inquiries
  ! that have not been answered yet
  ! 
  nreqst     = nv - n_answers
  nreqst_max = nreqst

  !
  ! Choice of maxspace should be adjusted to account for a default
  ! "sensible" size and/or a user-specified value
  !
  tmpv(1) = nadj
  tmpv(2) = nreqst_max
  tmpv(3) = n_row
  tmpv(4) = psb_cd_get_maxspace()
  call psb_max(ictxt,tmpv)
  nreqst_max = tmpv(2)
  locr_max = tmpv(3)
  maxspace = nt*locr_max
  if (tmpv(4) > 0) maxspace = min(maxspace,tmpv(4))
  maxspace = max(maxspace,np)
  if (trace.and.(me == 0)) write(0,*) ' Through graph_fnd_owner with maxspace:',maxspace
  if (do_timings) call psb_tic(idx_sweep0)
  if ((tmpv(1) > 0).and.(tmpv(2) >0)) then
    !
    ! Do a preliminary run on the user-defined adjacency lists
    !
    if (trace.and.(me == 0)) write(0,*) ' Initial sweep on user-defined topology'
    if (debugsz) write(0,*) me,' Initial sweep on user-defined topology',nreqst
    nsampl_in = min(nreqst,max(1,(maxspace+max(1,nadj)-1))/(max(1,nadj)))
    call psi_adj_fnd_sweep(idx,iprc,ladj,idxmap,nsampl_in,n_answers)  
    call idxmap%xtnd_p_adjcncy(ladj) 
    nreqst     = nv - n_answers
    nreqst_max = nreqst
    call psb_max(ictxt,nreqst_max)
    if (trace.and.(me == 0)) write(0,*) ' After initial sweep:',nreqst_max
    if (debugsz) write(0,*) me,' After sweep on user-defined topology',nreqst_max
  end if
  if (do_timings) call psb_toc(idx_sweep0)
    
  fnd_owner_loop: do while (nreqst_max>0)
    if (do_timings) call psb_tic(idx_loop_a2a)
    if (debugsz) write(0,*) me,' fnd_owner_loop',nreqst_max
    !
    ! The basic idea of this loop is to alternate between
    ! searching through all processes and searching
    ! in the neighbourood.
    !
    ! 1. Select a sample such that the total size is <= maxspace
    !    sample query is then sent to all processes
    !    
    ! if (trace.and.(me == 0)) write(0,*) 'Looping in graph_fnd_owner: ', nreqst_max
    nsampl_in = psb_cd_get_samplesize()
    nsampl_in = min(max(1,(maxspace+np-1)/np),nsampl_in)
    !
    ! Choose a sample, should it be done in this simplistic way?
    ! Note: nsampl_in is a hint, not an absolute, hence nsampl_out
    !
    ipnt = 1
    call psi_get_sample(ipnt, idx,iprc,tidx,tsmpl,nsampl_in,nsampl_out, pad=.true.)      
    nsampl_in = min(nsampl_out,nsampl_in)
    if (debugsz) write(0,*) me,' From first sampling ',nsampl_in
    ! 
    ! 2. Do a search on all processes; this is supposed to find
    !    the owning process for all inputs;
    !    
    call psi_a2a_fnd_owner(tidx(1:nsampl_in),tprc,idxmap,info, samesize=.true.)
    if (debugsz) write(0,*) me,' From a2a_fnd_owner ',info
    !
    ! We might have padded when looking for owners, so the actual samples
    ! could be less than they appear. Should be explained better.
    !
    nsampl_in = min(nreqst,nsampl_in)
    call psi_cpy_out(iprc,tprc,tsmpl,nsampl_in,nsampl_out)      
    if (nsampl_out /= nsampl_in) then 
      write(0,*) me,'Warning: indices not found by a2a_fnd_owner ',nsampl_out,nsampl_in
    end if
    n_answers = n_answers + nsampl_out
    nreqst    = nv - n_answers
    !
    ! 3. Extract the resulting adjacency list and add it to the
    !    indxmap;
    !
    ladj = tprc(1:nsampl_in)
    call psb_msort_unique(ladj,nadj)
    call psb_realloc(nadj,ladj,info)
    if (do_timings) call psb_toc(idx_loop_a2a)
    if (do_timings) call psb_tic(idx_loop_neigh)    
    !
    ! 4. Extract again a sample and do a neighbourhood search
    !    so that the total size is <= maxspace
    !    (will not be exact since nadj varies with process)
    !    Need to set up a proper loop here to have a complete
    !    sweep over the input vector. Done inside adj_fnd_sweep. 
    !
!!$      write(0,*) me,' After a2a ',nreqst
    nsampl_in = min(nreqst,max(1,(maxspace+max(1,nadj)-1))/(max(1,nadj)))
    mxnsin = nsampl_in
    call psb_max(ictxt,mxnsin)
!!$      write(0,*) me, ' mxnsin ',mxnsin
    if (mxnsin>0) call psi_adj_fnd_sweep(idx,iprc,ladj,idxmap,nsampl_in,n_answers)  
    call idxmap%xtnd_p_adjcncy(ladj) 

    nreqst     = nv - n_answers
    nreqst_max = nreqst
    call psb_max(ictxt,nreqst_max)
    if (trace.and.(me == 0)) write(0,*) ' fnd_owner_loop remaining:',nreqst_max
    if (do_timings) call psb_toc(idx_loop_neigh)    
  end do fnd_owner_loop

  call psb_erractionrestore(err_act)
  return

9999 call psb_error_handler(ictxt,err_act)

  return

contains

  subroutine psi_get_sample(ipntidx,idx,iprc,tidx,tsmpl,ns_in,ns_out,pad)      
    implicit none
    integer(psb_ipk_), intent(inout) :: ipntidx
    integer(psb_lpk_), intent(in)    :: idx(:)
    integer(psb_ipk_), intent(in)    :: ns_in, iprc(:)
    integer(psb_lpk_), intent(out)   :: tidx(:)
    integer(psb_ipk_), intent(out)   :: tsmpl(:), ns_out
    logical, intent(in), optional    :: pad
    !
    integer(psb_ipk_) :: nv, ns, k
    logical :: pad_

    if (present(pad)) then
      pad_ = pad
    else
      pad_ = .false.
    end if
    nv = size(idx)
    !
    ! Choose a sample, should it be done in this simplistic way? 
    !
    ns = ns_in
    !
    ! ns_in == 0 means that on the outside we figure there's
    ! nothing left, but we are here because we have to synchronize.
    ! Make sure we sweep through the entire vector immediately.
    ! But also make sure we do not overrun tsmpl
    ! 
    if (ns == 0) ns = nv
    ns = min(ns,size(tsmpl))
    ns_out = 0

    do while (ipntidx<= nv)
      if (iprc(ipntidx) == -1) then
        ns_out        = ns_out + 1
        tsmpl(ns_out) = ipntidx
        tidx(ns_out)  = idx(ipntidx)
      end if
      ipntidx = ipntidx + 1
      if (ns_out >= ns) exit
    end do
    if (pad_) then
      do k = ns_out+1, ns
        tsmpl(k) = -1
        tidx(k)  = -1
      end do
      ns_out = ns
    end if

  end subroutine psi_get_sample

  subroutine psi_cpy_out(iprc,tprc,tsmpl,ns_in,ns_out)      
    implicit none
    integer(psb_ipk_), intent(out) :: iprc(:)
    integer(psb_ipk_), intent(in)  :: ns_in
    integer(psb_ipk_), intent(in)  :: tprc(:), tsmpl(:)
    integer(psb_ipk_), intent(out) :: ns_out

    integer(psb_ipk_) :: j

    ns_out = 0 
    do j=1, ns_in
      if (tprc(j) /= -1) then
        ns_out = ns_out + 1
        iprc(tsmpl(j)) = tprc(j)
      end if
    end do
  end subroutine psi_cpy_out

  subroutine psi_adj_fnd_sweep(idx,iprc,adj,idxmap,n_samples,n_answers)      
    implicit none
    integer(psb_lpk_), intent(in)    :: idx(:)
    integer(psb_ipk_), intent(in)    :: n_samples
    integer(psb_ipk_), intent(inout) :: iprc(:), n_answers
    integer(psb_ipk_), intent(in)    :: adj(:)
    class(psb_indx_map), intent(inout) :: idxmap
    !
    integer(psb_ipk_) :: ipnt, ns_in, ns_out, n_rem, ictxt, me, np, isw
    integer(psb_lpk_), allocatable    :: tidx(:)
    integer(psb_ipk_), allocatable    :: tsmpl(:)

    ictxt   = idxmap%get_ctxt()
    call psb_info(ictxt,me,np)
    call psb_realloc(n_samples,tidx,info)
    call psb_realloc(n_samples,tsmpl,info)
    ipnt = 1
    isw  = 1
    do
      !write(0,*) me,' Into  sampling ',n_samples
      call psi_get_sample(ipnt, idx,iprc,tidx,tsmpl,n_samples,ns_out)      
      ns_in = min(n_samples,ns_out)
      !write(0,*) me,' From second sampling ',ns_out
      call psi_adjcncy_fnd_owner(tidx(1:ns_in),tprc,ladj,idxmap,info)
      call psi_cpy_out(iprc,tprc,tsmpl,ns_in,ns_out)
      !write(0,*) me,' Sweep ',isw,' answers:',ns_out
      n_answers = n_answers + ns_out
      n_rem = size(idx)-ipnt
      call psb_max(ictxt,n_rem)
      !write(0,*) me,' Sweep ',isw,n_rem, ipnt, n_samples
      if (n_rem <= 0) exit
      isw = isw + 1 
    end do


  end subroutine psi_adj_fnd_sweep

end subroutine psi_graph_fnd_owner