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Implement transeq in omp backend #27

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merged 21 commits into from
Feb 19, 2024
Merged

Implement transeq in omp backend #27

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ef3d02c
feat(omp): begin implementation of transeq solver
Nanoseb Jan 19, 2024
9a98a7f
feat(omp): initial transeq solver implementation
Nanoseb Jan 26, 2024
03754b7
feat(omp): handle multiplication inplace for convective flux
Nanoseb Jan 26, 2024
29f9f6a
docs(omp): add comment
Nanoseb Jan 26, 2024
e805ac0
refactor(omp): remove unusef vecmul_omp function
Nanoseb Feb 5, 2024
732f4da
refactor: refactor solver allocation of tdsops
Nanoseb Feb 6, 2024
237c61c
test: add test for omp transeq
Nanoseb Feb 6, 2024
b30271f
Fix typo in transeq computation
Nanoseb Feb 16, 2024
813804c
add dist_transeq test
Nanoseb Feb 16, 2024
33a24aa
remove unused variable
Nanoseb Feb 16, 2024
f7bc7e3
reformat long line
Nanoseb Feb 16, 2024
f11ec2e
Merge branch 'main' of github.com:xcompact3d/x3d2 into omp_transeq
Nanoseb Feb 16, 2024
3a327b9
add subroutine name after end subroutine
Nanoseb Feb 16, 2024
1646e53
add subroutine name after end subroutine
Nanoseb Feb 16, 2024
b20b503
improve performance of copy_into_buffers
Nanoseb Feb 16, 2024
6379a5d
Merge branch 'omp_transeq' of github.com:Nanoseb/x3d2 into omp_transeq
Nanoseb Feb 16, 2024
ddaaf7d
fix test_omp_transeq for parallel runs
Nanoseb Feb 16, 2024
aba7b1a
revert back to running tests in serial
Nanoseb Feb 16, 2024
6b63417
Explicitely set _dp in for transeq computation
Nanoseb Feb 16, 2024
e97c287
fix identation
Nanoseb Feb 19, 2024
33345c0
fix openmp race condition
Nanoseb Feb 19, 2024
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113 changes: 109 additions & 4 deletions src/omp/backend.f90
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@ module m_omp_backend
use m_base_backend, only: base_backend_t
use m_common, only: dp, globs_t
use m_tdsops, only: dirps_t, tdsops_t
use m_omp_exec_dist, only: exec_dist_tds_compact, exec_dist_transeq_compact
use m_omp_sendrecv, only: sendrecv_fields

use m_omp_common, only: SZ

Expand Down Expand Up @@ -30,6 +32,7 @@ module m_omp_backend
procedure :: vecadd => vecadd_omp
procedure :: set_fields => set_fields_omp
procedure :: get_fields => get_fields_omp
procedure :: transeq_omp_dist
end type omp_backend_t

interface omp_backend_t
Expand Down Expand Up @@ -118,7 +121,7 @@ subroutine transeq_x_omp(self, du, dv, dw, u, v, w, dirps)
class(field_t), intent(in) :: u, v, w
type(dirps_t), intent(in) :: dirps

!call self%transeq_omp_dist(du, dv, dw, u, v, w, dirps)
call self%transeq_omp_dist(du, dv, dw, u, v, w, dirps)

end subroutine transeq_x_omp

Expand All @@ -131,7 +134,7 @@ subroutine transeq_y_omp(self, du, dv, dw, u, v, w, dirps)
type(dirps_t), intent(in) :: dirps

! u, v, w is reordered so that we pass v, u, w
!call self%transeq_omp_dist(dv, du, dw, v, u, w, dirps)
call self%transeq_omp_dist(dv, du, dw, v, u, w, dirps)

end subroutine transeq_y_omp

Expand All @@ -144,10 +147,86 @@ subroutine transeq_z_omp(self, du, dv, dw, u, v, w, dirps)
type(dirps_t), intent(in) :: dirps

! u, v, w is reordered so that we pass w, u, v
!call self%transeq_omp_dist(dw, du, dv, w, u, v, dirps)
call self%transeq_omp_dist(dw, du, dv, w, u, v, dirps)

end subroutine transeq_z_omp

subroutine transeq_omp_dist(self, du, dv, dw, u, v, w, dirps)
implicit none

class(omp_backend_t) :: self
class(field_t), intent(inout) :: du, dv, dw
class(field_t), intent(in) :: u, v, w
type(dirps_t), intent(in) :: dirps
integer :: n_halo

call transeq_halo_exchange(self, u, v, w, dirps)

call transeq_dist_component(self, du, u, u, &
dirps%der1st, dirps%der1st_sym, dirps%der2nd, dirps)
call transeq_dist_component(self, dv, v, u, &
dirps%der1st_sym, dirps%der1st, dirps%der2nd_sym, dirps)
call transeq_dist_component(self, dw, w, u, &
dirps%der1st_sym, dirps%der1st, dirps%der2nd_sym, dirps)

end subroutine transeq_omp_dist


subroutine transeq_halo_exchange(self, u, v, w, dirps)
class(omp_backend_t) :: self
class(field_t), intent(in) :: u, v, w
type(dirps_t), intent(in) :: dirps
integer :: n_halo

! TODO: don't hardcode n_halo
n_halo = 4

call copy_into_buffers(self%u_send_s, self%u_send_e, u%data, dirps%n)
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call copy_into_buffers(self%v_send_s, self%v_send_e, v%data, dirps%n)
call copy_into_buffers(self%w_send_s, self%w_send_e, w%data, dirps%n)

call sendrecv_fields(self%u_recv_s, self%u_recv_e, self%u_send_s, self%u_send_e, &
SZ*n_halo*dirps%n_blocks, dirps%nproc, dirps%pprev, dirps%pnext)
call sendrecv_fields(self%v_recv_s, self%v_recv_e, self%v_send_s, self%v_send_e, &
SZ*n_halo*dirps%n_blocks, dirps%nproc, dirps%pprev, dirps%pnext)
call sendrecv_fields(self%w_recv_s, self%w_recv_e, self%w_send_s, self%w_send_e, &
SZ*n_halo*dirps%n_blocks, dirps%nproc, dirps%pprev, dirps%pnext)

end subroutine
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Is it okay to omit subroutine name here? On github it broke the syntax highlighting for me in the subroutine below.

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yes, it is never a requirement (maybe it used to be in older standards?). It is weird indeed that github syntax highlight doesn't handle it. I can add it if needed.

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!> Computes RHS_x^v following:
! rhs_x^v = -0.5*(u*dv/dx + duv/dx) + nu*d2v/dx2
subroutine transeq_dist_component(self, rhs, v, u, tdsops_du, tdsops_dud, tdsops_d2u, dirps)

class(omp_backend_t) :: self
class(field_t), intent(inout) :: rhs
class(field_t), intent(in) :: u, v
class(tdsops_t), intent(in) :: tdsops_du
class(tdsops_t), intent(in) :: tdsops_dud
class(tdsops_t), intent(in) :: tdsops_d2u
type(dirps_t), intent(in) :: dirps
class(field_t), pointer :: du, d2u, dud

du => self%allocator%get_block()
dud => self%allocator%get_block()
d2u => self%allocator%get_block()

call exec_dist_transeq_compact(&
rhs%data, du%data, dud%data, d2u%data, &
self%du_send_s, self%du_send_e, self%du_recv_s, self%du_recv_e, &
self%dud_send_s, self%dud_send_e, self%dud_recv_s, self%dud_recv_e, &
self%d2u_send_s, self%d2u_send_e, self%d2u_recv_s, self%d2u_recv_e, &
u%data, self%u_recv_s, self%u_recv_e, &
v%data, self%v_recv_s, self%v_recv_e, &
tdsops_du, tdsops_dud, tdsops_d2u, self%nu, &
dirps%nproc, dirps%pprev, dirps%pnext, dirps%n_blocks)

call self%allocator%release_block(du)
call self%allocator%release_block(dud)
call self%allocator%release_block(d2u)

end subroutine
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subroutine tds_solve_omp(self, du, u, dirps, tdsops)
implicit none

Expand All @@ -157,10 +236,36 @@ subroutine tds_solve_omp(self, du, u, dirps, tdsops)
type(dirps_t), intent(in) :: dirps
class(tdsops_t), intent(in) :: tdsops

!call self%tds_solve_dist(self, du, u, dirps, tdsops)
call tds_solve_dist(self, du, u, dirps, tdsops)

end subroutine tds_solve_omp

subroutine tds_solve_dist(self, du, u, dirps, tdsops)
implicit none

class(omp_backend_t) :: self
class(field_t), intent(inout) :: du
class(field_t), intent(in) :: u
type(dirps_t), intent(in) :: dirps
class(tdsops_t), intent(in) :: tdsops
integer :: n_halo

! TODO: don't hardcode n_halo
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n_halo = 4
call copy_into_buffers(self%u_send_s, self%u_send_e, u%data, dirps%n)

! halo exchange
call sendrecv_fields(self%u_recv_s, self%u_recv_e, self%u_send_s, self%u_send_e, &
SZ*n_halo*dirps%n_blocks, dirps%nproc, dirps%pprev, dirps%pnext)


call exec_dist_tds_compact( &
du%data, u%data, self%u_recv_s, self%u_recv_e, self%du_send_s, self%du_send_e, &
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self%du_recv_s, self%du_recv_e, &
tdsops, dirps%nproc, dirps%pprev, dirps%pnext, dirps%n_blocks)

end subroutine tds_solve_dist

subroutine reorder_omp(self, u_, u, direction)
implicit none

Expand Down
129 changes: 129 additions & 0 deletions src/omp/exec_dist.f90
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Original file line number Diff line number Diff line change
Expand Up @@ -61,5 +61,134 @@ subroutine exec_dist_tds_compact( &

end subroutine exec_dist_tds_compact


subroutine exec_dist_transeq_compact(&
rhs, du, dud, d2u, &
du_send_s, du_send_e, du_recv_s, du_recv_e, &
dud_send_s, dud_send_e, dud_recv_s, dud_recv_e, &
d2u_send_s, d2u_send_e, d2u_recv_s, d2u_recv_e, &
u, u_recv_s, u_recv_e, &
v, v_recv_s, v_recv_e, &
tdsops_du, tdsops_dud, tdsops_d2u, nu, nproc, pprev, pnext, n_block)

implicit none

! du = d(u)
real(dp), dimension(:, :, :), intent(out) :: rhs, du, dud, d2u

! The ones below are intent(out) just so that we can write data in them,
! not because we actually need the data they store later where this
! subroutine is called. We absolutely don't care about the data they pass back
real(dp), dimension(:, :, :), intent(out) :: &
du_send_s, du_send_e, du_recv_s, du_recv_e
real(dp), dimension(:, :, :), intent(out) :: &
dud_send_s, dud_send_e, dud_recv_s, dud_recv_e
real(dp), dimension(:, :, :), intent(out) :: &
d2u_send_s, d2u_send_e, d2u_recv_s, d2u_recv_e

real(dp), dimension(:, :, :), intent(in) :: u, u_recv_s, u_recv_e
real(dp), dimension(:, :, :), intent(in) :: v, v_recv_s, v_recv_e

type(tdsops_t), intent(in) :: tdsops_du, tdsops_dud, tdsops_d2u

real(dp), dimension(:, :), allocatable :: ud, ud_recv_s, ud_recv_e
real(dp) :: nu
integer, intent(in) :: nproc, pprev, pnext
integer, intent(in) :: n_block

integer :: n_data, n_halo
integer :: k, i, j, n

! TODO: don't hardcode n_halo
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n_halo = 4
n = tdsops_d2u%n
n_data = SZ*n_block

allocate(ud(SZ, n))
allocate(ud_recv_e(SZ, n_halo))
allocate(ud_recv_s(SZ, n_halo))

!$omp parallel do
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do k = 1, n_block
call der_univ_dist( &
du(:, :, k), du_send_s(:, :, k), du_send_e(:, :, k), u(:, :, k), &
u_recv_s(:, :, k), u_recv_e(:, :, k), &
tdsops_du%coeffs_s, tdsops_du%coeffs_e, tdsops_du%coeffs, tdsops_du%n, &
tdsops_du%dist_fw, tdsops_du%dist_bw, tdsops_du%dist_af &
)

call der_univ_dist( &
d2u(:, :, k), d2u_send_s(:, :, k), d2u_send_e(:, :, k), u(:, :, k), &
u_recv_s(:, :, k), u_recv_e(:, :, k), &
tdsops_d2u%coeffs_s, tdsops_d2u%coeffs_e, tdsops_d2u%coeffs, tdsops_d2u%n, &
tdsops_d2u%dist_fw, tdsops_d2u%dist_bw, tdsops_d2u%dist_af &
)

! Handle dud by locally generating u*v
do j = 1, n
!$omp simd
do i = 1, SZ
ud(i, j) = u(i, j, k) * v(i, j, k)
end do
!$omp end simd
end do

do j = 1, n_halo
!$omp simd
do i = 1, SZ
ud_recv_s(i, j) = u_recv_s(i, j, k) * v_recv_s(i, j, k)
ud_recv_e(i, j) = u_recv_e(i, j, k) * v_recv_e(i, j, k)
end do
!$omp end simd
end do

call der_univ_dist( &
dud(:, :, k), dud_send_s(:, :, k), dud_send_e(:, :, k), ud(:, :), &
ud_recv_s(:, :), ud_recv_e(:, :), &
tdsops_dud%coeffs_s, tdsops_dud%coeffs_e, tdsops_dud%coeffs, tdsops_dud%n, &
tdsops_dud%dist_fw, tdsops_dud%dist_bw, tdsops_dud%dist_af &
)

end do
!$omp end parallel do

! halo exchange for 2x2 systems
call sendrecv_fields(du_recv_s, du_recv_e, du_send_s, du_send_e, &
n_data, nproc, pprev, pnext)
call sendrecv_fields(dud_recv_s, dud_recv_e, dud_send_s, dud_send_e, &
n_data, nproc, pprev, pnext)
call sendrecv_fields(d2u_recv_s, d2u_recv_e, d2u_send_s, d2u_send_e, &
n_data, nproc, pprev, pnext)

!$omp parallel do
do k = 1, n_block
call der_univ_subs(du(:, :, k), &
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I realised that here we're writing 3 field sized arrays into main memory unnecessarily. It is potentially increasing the runtime %20.

In the second phase of the algorithm here we pass a part of the du, dud, and d2u into der_univ_subs, and they're all rewritten in place. Then later we combine them in rhs for the final result. Ideally, we want du, dud, and d2u to be read once and rhs to be written only once. However because of the way der_univ_subs work, the updated data in du arrays after der_univ_subs call gets written in the main memory, even though we don't need this at all.

There are three ways we can fix this

  • In the parallel do loop in the second phase we can copy the relevant parts of du, dud, and d2u arrays into (SZ, n) sized temporary arrays. Then we pass temporary arrays into der_univ_subs, and at the end we use these temporaries to obtain final rhs. This is the easiest solution but it may not be the best in terms of performance.
  • We can write an alternative der_univ_subs and separate input and output arrays. This way we can pass a part of the du arrays as we do now, and pass a small temporary array as the output one. Because du arrays will be input arrays no data will be written in main memory. Then we can combine the temporaries to get rhs.
  • If we're writing an alternative der_univ_subs to be used in transeq, we can go one step further and have a fused version of it. This would probably the most performant solution. der_univ_subs is relatively lightweight so it isn't really hard to do so. The new subrotuine can input all du, dud, and d2u, and write the final result rhs.

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#40 is relevant here

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Good points, I will have a think about it, but indeed having it in a new PR focusing on performance makes sense.

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Alright, I think best way to move forward is implementing the first strategy and checking how much of the peak BW we get. If its a good utilisation then maybe we don't need to bother with a new der_univ_subs at all.

du_recv_s(:, :, k), du_recv_e(:, :, k), &
tdsops_du%n, tdsops_du%dist_sa, tdsops_du%dist_sc)

call der_univ_subs(dud(:, :, k), &
dud_recv_s(:, :, k), dud_recv_e(:, :, k), &
tdsops_dud%n, tdsops_dud%dist_sa, tdsops_dud%dist_sc)

call der_univ_subs(d2u(:, :, k), &
d2u_recv_s(:, :, k), d2u_recv_e(:, :, k), &
tdsops_d2u%n, tdsops_d2u%dist_sa, tdsops_d2u%dist_sc)

do j = 1, n
!$omp simd
do i = 1, SZ
rhs(i, j, k) = -0.5*(v(i, j, k)*du(i, j, k) + dud(i, j, k)) + nu*d2u(i, j, k)
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end do
!$omp end simd
end do

end do
!$omp end parallel do


end subroutine exec_dist_transeq_compact



end module m_omp_exec_dist

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