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[UPDATE] Drop the MPI_Info window hints, measured to have no effect

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Paired A/B at 448 ranks, three replicas per arm inside one allocation: with
no_locks=true the aggregated MPI_Win_create cost 1463 s against 1450 s
without it, the two ranges fully overlapping. A probe with MPI_Win_get_info
confirmed this Open MPI retains the hint, so the null result belongs to the
hint and not to a failed measurement; same_disp_unit was silently ignored.

Removes the cached MPI_Info handles and their helpers, and returns the four
PSCW win_create calls to MPI_INFO_NULL.
This commit is contained in:
Stack-1
2026-08-14 16:43:59 +02:00
parent 9b3b63656e
commit d569cd4020
2 changed files with 9 additions and 95 deletions
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base/modules/comm/comm_schemes/psb_comm_rma_mod.F90
-62
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@@ -15,23 +15,6 @@ module psb_comm_rma_mod
include 'mpif.h'
#endif
! Hints attached to every window created by the one-sided schemes.
!
! Given no info at all, the implementation has to stay ready for the general
! case: a passive-target lock could arrive at any moment, and ranks could have
! passed different displacement units. Staying ready is not free -- it costs
! metadata exchanged among all ranks on each creation -- and creation is where
! these schemes spend most of their time. The assertions below hold here and
! cost nothing to make.
!
! Deliberately NOT asserted: same_size. Halo buffers are sized by the local
! halo, which differs from rank to rank, so that assertion would be false.
!
! Cached for the life of the program: the hints never change, and building an
! info object per window would add to the very cost this is meant to remove.
integer(psb_mpk_), private, save :: rma_wininfo_pscw = mpi_info_null
integer(psb_mpk_), private, save :: rma_wininfo_gen = mpi_info_null
type, extends(psb_comm_handle_type) :: psb_comm_rma_handle
integer(psb_mpk_) :: win = mpi_win_null
logical :: window_ready = .false.
@@ -68,51 +51,6 @@ module psb_comm_rma_mod
contains
! Return the MPI_Info to pass to mpi_win_create, building it on first use.
! no_locks must be .true. only where the window is synchronized exclusively
! with PSCW: it asserts that no passive-target epoch will ever be opened on
! it, and a win_lock afterwards would be erroneous. Today that is the double
! precision swapdata path; every other path still takes locks.
subroutine psb_comm_rma_get_wininfo(winfo, no_locks, info)
integer(psb_mpk_), intent(out) :: winfo
logical, intent(in) :: no_locks
integer(psb_ipk_), intent(out) :: info
info = psb_success_
if (no_locks) then
if (rma_wininfo_pscw == mpi_info_null) then
call psb_comm_rma_build_wininfo(rma_wininfo_pscw, .true., info)
if (info /= psb_success_) return
end if
winfo = rma_wininfo_pscw
else
if (rma_wininfo_gen == mpi_info_null) then
call psb_comm_rma_build_wininfo(rma_wininfo_gen, .false., info)
if (info /= psb_success_) return
end if
winfo = rma_wininfo_gen
end if
end subroutine psb_comm_rma_get_wininfo
subroutine psb_comm_rma_build_wininfo(winfo, no_locks, info)
integer(psb_mpk_), intent(out) :: winfo
logical, intent(in) :: no_locks
integer(psb_ipk_), intent(out) :: info
integer(psb_mpk_) :: iret
info = psb_success_
winfo = mpi_info_null
call mpi_info_create(winfo, iret)
if (iret /= mpi_success) then
info = psb_err_mpi_error_
winfo = mpi_info_null
return
end if
! Every rank passes the size of one element of the same type.
call mpi_info_set(winfo, 'same_disp_unit', 'true', iret)
if (no_locks) call mpi_info_set(winfo, 'no_locks', 'true', iret)
end subroutine psb_comm_rma_build_wininfo
subroutine psb_comm_rma_init(this, info)
class(psb_comm_rma_handle), intent(inout) :: this
integer(psb_ipk_), intent(out) :: info