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GPU stack 1/8: update feectools (device ghost exchange, single-reduction PCG); pcg_sr solver option - #782

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Part 1 of 8 of the split of #772 (cuda-aware-mpi-fixes) into stacked PRs. Requires struphy-hub/feectools#104 to be merged into feectools devel-tiny first (PR 1 bumps the submodule).

Merge struphy-hub/feectools#104 (feectools fix-cuda-aware-mpi-issues into devel-tiny) first. This PR points the feectools submodule at that branch (commit 1d8d47c).

  • Submodule update: device ghost-exchange plans, fused block exchanges, PConjugateGradientSingleReduction, faster stencil_dot_3d on the GPU (details in the feectools PR).
  • pcg_sr is accepted wherever pcg is (LiteralOptions.OptsSymmSolver), also with a preconditioner: Poisson, ImplicitDiffusion, GyrokineticPoissonSolve, CurlCurlSolve, VariationalDensityEvolve, VariationalMomentumAdvection. Same iterates as pcg, one global reduction per iteration instead of two.

Tests

Local, macOS without a GPU, in a fresh environment with feectools 1d8d47c and the pinned cunumpy, after merging devel (with #774 and #775). The PR passes test_cuda_parity, test_cuda_emulation, test_kernel_backends, test_sorting, test_accum_matrix_cupy, test_preconditioner_cupy, test_poisson and test_output on its own. The top of the stack also passes the mass-matrix, preconditioner, Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén, post-processing, polar fake-CuPy and all pic tests (1477 passed), the examples test for the two profiling cases, the sorting, Poisson and fused-gradient tests under mpirun -n 2, and the device MPI sort on the fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid, periodic and Dirichlet, on 1 and 2 ranks.
Not tested on a GPU here. The CUDA kernels and the device paths need a run on the cluster.

Stack (merge in order)

  1. Device ghost-exchange plans, fused block exchanges, single-reduction PCG (CUDA-aware MPI) feectools#104 (feectools, into devel-tiny)
# PR base
1 #782 update feectools (device ghost exchange, single-reduction PCG); pcg_sr solver option (this PR) devel
2 #783 host/device conversions in post-processing; math.sqrt in Species #782
3 #784 CUDA mass-matrix assembly kernel kernel_3d_mat #783
4 #785 apply separable mass matrices as Kronecker products of 1D banded matrices #784
5 #786 Poisson/diffusion solve with fewer passes over the vectors #785
6 #787 marker rows prepared inside the push kernels #786
7 #788 chunked marker loading, row-based weight update, leaner MPI sorting; static field in PushVxB #787
8 #789 profiling cases Poisson cube and Vlasov slab (CPU node vs GPU, GPU scaling) #788

🤖 Generated with Claude Code

… add the pcg_sr solver option

feectools: struphy-hub/feectools#104 (fix-cuda-aware-mpi-issues into devel-tiny).
pcg_sr (PConjugateGradientSingleReduction) is accepted wherever pcg is, including the
preconditioned solvers of the Poisson, diffusion, curl-curl and variational propagators.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
max-models and others added 6 commits October 16, 2026 12:51
feectools b70cb6c (struphy-hub/feectools#104): the emulated GPU tests (fake CuPy) failed at the
first stencil product.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
feectools 1d8d47c (struphy-hub/feectools#104).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…shear Alfven solves

ShearAlfven and ShearAlfvenCurlCurl (#778, #780) accepted these preconditioners only with
solver='pcg'; pcg_sr takes a preconditioner as well, as in the other propagators.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@max-models
max-models marked this pull request as draft October 22, 2026 06:39
@max-models
max-models marked this pull request as ready for review October 23, 2026 07:15
@max-models
max-models requested a review from spossann October 23, 2026 07:15
spossann
spossann previously approved these changes Oct 24, 2026

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Bump feectools and good to go 👍

@max-models
max-models merged commit 773c93b into devel Oct 24, 2026
28 checks passed
@max-models
max-models deleted the gpu-stack-1-feectools branch October 24, 2026 19:03
max-models added a commit that referenced this pull request Oct 24, 2026
…in Species (#783)

Part 2 of 8 of the split of #772 (`cuda-aware-mpi-fixes`) into stacked
PRs. **Requires struphy-hub/feectools#104 to be
merged into feectools `devel-tiny` first** (PR 1 bumps the submodule).

- `post_processing/output.py`: on the CuPy backend the fields are
evaluated on the device and written from the host. The evaluation grids,
point data and coordinates are converted where they cross, and HDF5 data
is moved to the device before it goes into the spline coefficients.
- `Species`: the plasma frequency of the unit conversion is a host
scalar (`math.sqrt` instead of `xp.sqrt`).

## Tests

Local, macOS without a GPU, in a fresh environment with feectools
`1d8d47c` and the pinned cunumpy, after merging devel (with #774 and
#775). The PR passes `test_cuda_parity`, `test_cuda_emulation`,
`test_kernel_backends`, `test_sorting`, `test_accum_matrix_cupy`,
`test_preconditioner_cupy`, `test_poisson` and `test_output` on its own.
The top of the stack also passes the mass-matrix, preconditioner,
Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén,
post-processing, polar fake-CuPy and all `pic` tests (1477 passed), the
examples test for the two profiling cases, the sorting, Poisson and
fused-gradient tests under `mpirun -n 2`, and the device MPI sort on the
fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil
mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid,
periodic and Dirichlet, on 1 and 2 ranks.
**Not tested on a GPU here.** The CUDA kernels and the device paths need
a run on the cluster.

## Stack (merge in order)

0. struphy-hub/feectools#104 (feectools, into
`devel-tiny`)

| # | PR | base |
|---|---|---|
| 1 | #782 update feectools (device ghost exchange, single-reduction
PCG); pcg_sr solver option | `devel` |
| 2 | #783 host/device conversions in post-processing; math.sqrt in
Species **(this PR)** | #782 |
| 3 | #784 CUDA mass-matrix assembly kernel kernel_3d_mat | #783 |
| 4 | #785 apply separable mass matrices as Kronecker products of 1D
banded matrices | #784 |
| 5 | #786 Poisson/diffusion solve with fewer passes over the vectors |
#785 |
| 6 | #787 marker rows prepared inside the push kernels | #786 |
| 7 | #788 chunked marker loading, row-based weight update, leaner MPI
sorting; static field in PushVxB | #787 |
| 8 | #789 profiling cases Poisson cube and Vlasov slab (CPU node vs
GPU, GPU scaling) | #788 |

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
max-models added a commit that referenced this pull request Oct 24, 2026
Part 3 of 8 of the split of #772 (`cuda-aware-mpi-fixes`) into stacked
PRs. **Requires struphy-hub/feectools#104 to be
merged into feectools `devel-tiny` first** (PR 1 bumps the submodule).

- `kernel_3d_mat_cuda.cu`: one thread per (element, codomain basis
function, domain basis function). It replaces the host fallback on the
CuPy backend (`missing_cuda="fallback"` removed, launch size from
`n_threads_from`).
- `WeightedMassOperator.assemble` reads the quadrature grids (spans,
weights, basis values) as backend arrays, copied to the device once and
cached.
- `Simulation.allocate` compiles the assembly kernel before the first
assembly, in its own profiling region (`setup: compile cuda kernels
(assembly)`), so the ~1 s compilation is not counted in the assembly.

Added while splitting: parity cases for `kernel_3d_mat` (random
quadrature data on 3×2×2 elements with mixed degrees, with and without a
ghost row). `test_cuda_kernels_have_parity_cases` requires one for every
kernel with a CUDA version. The emulation test confirms that the CUDA
kernel matches the pyccel kernel without a GPU.

## Tests

Local, macOS without a GPU, in a fresh environment with feectools
`1d8d47c` and the pinned cunumpy, after merging devel (with #774 and
#775). The PR passes `test_cuda_parity`, `test_cuda_emulation`,
`test_kernel_backends`, `test_sorting`, `test_accum_matrix_cupy`,
`test_preconditioner_cupy`, `test_poisson` and `test_output` on its own.
The top of the stack also passes the mass-matrix, preconditioner,
Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén,
post-processing, polar fake-CuPy and all `pic` tests (1477 passed), the
examples test for the two profiling cases, the sorting, Poisson and
fused-gradient tests under `mpirun -n 2`, and the device MPI sort on the
fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil
mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid,
periodic and Dirichlet, on 1 and 2 ranks.
**Not tested on a GPU here.** The CUDA kernels and the device paths need
a run on the cluster.

## Stack (merge in order)

0. struphy-hub/feectools#104 (feectools, into
`devel-tiny`)

| # | PR | base |
|---|---|---|
| 1 | #782 update feectools (device ghost exchange, single-reduction
PCG); pcg_sr solver option | `devel` |
| 2 | #783 host/device conversions in post-processing; math.sqrt in
Species | #782 |
| 3 | #784 CUDA mass-matrix assembly kernel kernel_3d_mat **(this PR)**
| #783 |
| 4 | #785 apply separable mass matrices as Kronecker products of 1D
banded matrices | #784 |
| 5 | #786 Poisson/diffusion solve with fewer passes over the vectors |
#785 |
| 6 | #787 marker rows prepared inside the push kernels | #786 |
| 7 | #788 chunked marker loading, row-based weight update, leaner MPI
sorting; static field in PushVxB | #787 |
| 8 | #789 profiling cases Poisson cube and Vlasov slab (CPU node vs
GPU, GPU scaling) | #788 |

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
max-models added a commit that referenced this pull request Oct 24, 2026
… 1D banded matrices (#785)

Part 4 of 8 of the split of #772 (`cuda-aware-mpi-fixes`) into stacked
PRs. **Requires struphy-hub/feectools#104 to be
merged into feectools `devel-tiny` first** (PR 1 bumps the submodule).

- `feec/kronecker_mass.py`: `WeightedMassOperator.dot` applies the
blocks of its matrix that are Kronecker products of 1D banded matrices
(constant weights, e.g. on a Cuboid) as three banded passes instead of
the 3D stencil product. On the GPU this uses the new kernel
`kron_band_pass_cuda.cu`. `STRUPHY_KRONECKER_MASS=0` switches it off.
- The replacement is built on first use and invalidated by assembly,
copies and in-place arithmetic. A matrix changed by arithmetic that is
not a Kronecker product (e.g. a Schur complement rebuilt every step) is
not checked again.
- The boundary and extraction operators around the matrix are skipped
when they are identities, instead of being applied as copies.

- The band-pass kernel is launched through feectools' `CachedLaunch`
(feectools#104): the banded passes run with the same buffers in every
solver iteration, so the launch preparation is done once per set of
buffers.

## Tests

Local, macOS without a GPU, in a fresh environment with feectools
`1d8d47c` and the pinned cunumpy, after merging devel (with #774 and
#775). The PR passes `test_cuda_parity`, `test_cuda_emulation`,
`test_kernel_backends`, `test_sorting`, `test_accum_matrix_cupy`,
`test_preconditioner_cupy`, `test_poisson` and `test_output` on its own.
The top of the stack also passes the mass-matrix, preconditioner,
Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén,
post-processing, polar fake-CuPy and all `pic` tests (1477 passed), the
examples test for the two profiling cases, the sorting, Poisson and
fused-gradient tests under `mpirun -n 2`, and the device MPI sort on the
fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil
mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid,
periodic and Dirichlet, on 1 and 2 ranks.
**Not tested on a GPU here.** The CUDA kernels and the device paths need
a run on the cluster.

## Stack (merge in order)

0. struphy-hub/feectools#104 (feectools, into
`devel-tiny`)

| # | PR | base |
|---|---|---|
| 1 | #782 update feectools (device ghost exchange, single-reduction
PCG); pcg_sr solver option | `devel` |
| 2 | #783 host/device conversions in post-processing; math.sqrt in
Species | #782 |
| 3 | #784 CUDA mass-matrix assembly kernel kernel_3d_mat | #783 |
| 4 | #785 apply separable mass matrices as Kronecker products of 1D
banded matrices **(this PR)** | #784 |
| 5 | #786 Poisson/diffusion solve with fewer passes over the vectors |
#785 |
| 6 | #787 marker rows prepared inside the push kernels | #786 |
| 7 | #788 chunked marker loading, row-based weight update, leaner MPI
sorting; static field in PushVxB | #787 |
| 8 | #789 profiling cases Poisson cube and Vlasov slab (CPU node vs
GPU, GPU scaling) | #788 |

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
max-models added a commit that referenced this pull request Oct 24, 2026
…tors (#786)

Part 5 of 8 of the split of #772 (`cuda-aware-mpi-fixes`) into stacked
PRs. **Requires struphy-hub/feectools#104 to be
merged into feectools `devel-tiny` first** (PR 1 bumps the submodule).

- `BoundaryOperator.dot` on device Stencil/Block vectors computes `out =
v * mask`, one kernel per block (one for all blocks when they are
contiguous float64). The masks are found once from
`apply_essential_bc_to_array`, so they zero exactly the same entries.
This replaces a copy and one fill per boundary and component.
- `WeightedMassOperator.without_boundary_ops()` /
`MassWithoutBoundaryOps`: the mass operator without its boundary
operators. In `grad.T @ M1 @ grad`, `grad` already applies the same 0/1
masks, so this is the same operator with two fewer passes per product.
It is not used with the multigrid preconditioner.
- `ImplicitDiffusion`: the automatic `1e-14` stabilization stays out of
the solver operator when a Dirichlet boundary already makes `grad.T M1
grad` positive definite. There is no `stab_mat` product for the
right-hand side when `sigma_2 = 0` (Poisson).

- `struphy.feec.fused_derivatives`:
`fuse_boundary_gradient(derham.grad)` and
`fuse_boundary_gradient(derham.grad.T)` apply `B_out G B_in` with one
CUDA kernel each on the GPU (`fused_derivatives_cuda.cu`), instead of a
masked copy, three derivatives and a masked copy. The kernel does the
same operations in the same order, so the products are bit for bit those
of the composed operators. It reads the input with its ghost regions
exchanged, times the input mask with exchanged ghost regions, which
equals the exchanged masked input in serial and in parallel. Host data
and the fake CuPy use the composed operators. `ImplicitDiffusion` uses
it for `grad` and `grad.T` (not with the multigrid preconditioner). The
original branch imported this module, but it was never committed, so it
is written new here. `test_fused_derivatives` compares the kernels with
the composed operators on the fake CuPy with emulated launches, and
guards that the kernels actually run.

Also added: the fused mask kernel is skipped on cunumpy's fake CuPy,
which cannot launch raw kernels (`test_mass_preconditioners_fake_cupy`
failed).

## Tests

Local, macOS without a GPU, in a fresh environment with feectools
`1d8d47c` and the pinned cunumpy, after merging devel (with #774 and
#775). The PR passes `test_cuda_parity`, `test_cuda_emulation`,
`test_kernel_backends`, `test_sorting`, `test_accum_matrix_cupy`,
`test_preconditioner_cupy`, `test_poisson` and `test_output` on its own.
The top of the stack also passes the mass-matrix, preconditioner,
Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén,
post-processing, polar fake-CuPy and all `pic` tests (1477 passed), the
examples test for the two profiling cases, the sorting, Poisson and
fused-gradient tests under `mpirun -n 2`, and the device MPI sort on the
fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil
mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid,
periodic and Dirichlet, on 1 and 2 ranks.
**Not tested on a GPU here.** The CUDA kernels and the device paths need
a run on the cluster.

## Stack (merge in order)

0. struphy-hub/feectools#104 (feectools, into
`devel-tiny`)

| # | PR | base |
|---|---|---|
| 1 | #782 update feectools (device ghost exchange, single-reduction
PCG); pcg_sr solver option | `devel` |
| 2 | #783 host/device conversions in post-processing; math.sqrt in
Species | #782 |
| 3 | #784 CUDA mass-matrix assembly kernel kernel_3d_mat | #783 |
| 4 | #785 apply separable mass matrices as Kronecker products of 1D
banded matrices | #784 |
| 5 | #786 Poisson/diffusion solve with fewer passes over the vectors
**(this PR)** | #785 |
| 6 | #787 marker rows prepared inside the push kernels | #786 |
| 7 | #788 chunked marker loading, row-based weight update, leaner MPI
sorting; static field in PushVxB | #787 |
| 8 | #789 profiling cases Poisson cube and Vlasov slab (CPU node vs
GPU, GPU scaling) | #788 |

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
max-models added a commit that referenced this pull request Oct 24, 2026
Part 6 of 8 of the split of #772 (`cuda-aware-mpi-fixes`) into stacked
PRs. **Requires struphy-hub/feectools#104 to be
merged into feectools `devel-tiny` first** (PR 1 bumps the submodule).

- `push_eta_stage` and `push_vxb_analytic` prepare each marker
themselves at stage 0 (`MarkerArgs.prepare_rows`): they copy the
phase-space coordinates to the rows from `first_pusher_idx` and zero the
rows after them, as `prepare_push` does. `Pusher._push` then skips the
separate `prepare_push` launch when no init or evaluation kernel runs
before them (those may read the prepared rows). The kernels cover the
same markers, one thread per used marker (`n_markers_used`).
- `prepare_rows` is a CUDA-only field of `MarkerArgs`. The CUDA
emulation of the tests reads it with default 0.

Updated after #774 and #775 were merged into devel: on the original
branch this PR also stored the marker buffer column-major on the GPU
(`order="F"`). devel now stores it as `(n_cols, n_markers)` on both
backends, so that part is gone. The row preparation is ported to
`markers(j, ip)` indexing.

## Tests

Local, macOS without a GPU, in a fresh environment with feectools
`1d8d47c` and the pinned cunumpy, after merging devel (with #774 and
#775). The PR passes `test_cuda_parity`, `test_cuda_emulation`,
`test_kernel_backends`, `test_sorting`, `test_accum_matrix_cupy`,
`test_preconditioner_cupy`, `test_poisson` and `test_output` on its own.
The top of the stack also passes the mass-matrix, preconditioner,
Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén,
post-processing, polar fake-CuPy and all `pic` tests (1477 passed), the
examples test for the two profiling cases, the sorting, Poisson and
fused-gradient tests under `mpirun -n 2`, and the device MPI sort on the
fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil
mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid,
periodic and Dirichlet, on 1 and 2 ranks.
**Not tested on a GPU here.** The CUDA kernels and the device paths need
a run on the cluster.

## Stack (merge in order)

0. struphy-hub/feectools#104 (feectools, into
`devel-tiny`)

| # | PR | base |
|---|---|---|
| 1 | #782 update feectools (device ghost exchange, single-reduction
PCG); pcg_sr solver option | `devel` |
| 2 | #783 host/device conversions in post-processing; math.sqrt in
Species | #782 |
| 3 | #784 CUDA mass-matrix assembly kernel kernel_3d_mat | #783 |
| 4 | #785 apply separable mass matrices as Kronecker products of 1D
banded matrices | #784 |
| 5 | #786 Poisson/diffusion solve with fewer passes over the vectors |
#785 |
| 6 | #787 marker rows prepared inside the push kernels **(this PR)** |
#786 |
| 7 | #788 chunked marker loading, row-based weight update, leaner MPI
sorting; static field in PushVxB | #787 |
| 8 | #789 profiling cases Poisson cube and Vlasov slab (CPU node vs
GPU, GPU scaling) | #788 |

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
max-models added a commit that referenced this pull request Oct 27, 2026
…r MPI sorting; static field in PushVxB (#788)

Part 7 of 8 of the split of #772 (`cuda-aware-mpi-fixes`) into stacked
PRs. **Requires struphy-hub/feectools#104 to be
merged into feectools `devel-tiny` first** (PR 1 bumps the submodule).

- Pseudo-random markers are drawn in chunks of `2**20` (was 10000): 16
instead of 1600 iterations for 16M markers, each a few small kernels and
a device sync on the GPU. The NumPy draws do not depend on the chunk
size.
- `update_weights` finds the indices of the valid markers once and reads
only the quantities it needs (`xp.take` of one row of the buffer each),
instead of a boolean selection per property and a count of the valid
markers.
- `mpi_sort_markers`: the ghost bookkeeping is skipped without sorting
boxes, where no ghosts can exist. There are no barriers around the
device exchange, which waits for every send and receive
(`cunumpy.mpi.exchange`). The host path keeps them. The sorting
positions for `alpha = 1` are one add instead of five kernels.
- `PushVxB` without a magnetic field variable computes the total field
once, so there is no ghost exchange (an MPI synchronization point)
before every push.

- Device MPI sort (`Particles._mpi_sort_device`,
`struphy.pic.mpi_sort_cuda`): on the GPU one kernel
(`sort_destinations`) finds the destination of every marker and counts
the markers per destination, instead of a pass over the buffer per
direction and per rank. The leaving markers are listed once, stably
sorted by destination and gathered once per destination rank. The result
is that of the host path (the same markers in the same columns; lost
markers become holes), at the cost of one 8-byte read per rank for the
counts. `STRUPHY_DEVICE_SORT=1` or `0` forces it on (also on the fake
CuPy) or off. The original branch imported `mpi_sort_cuda`, but it was
never committed (and called an undefined `_to_numpy_for_kernel`), so it
is written new here for the `(n_cols, n_markers)` buffer of devel.
`test_mpi_sort_markers_device_kernel_fake_cupy` compares it with the
NumPy sort, CUDA-aware and staged, periodic and removing boundaries, on
2 and 4 ranks.

## Tests

Local, macOS without a GPU, in a fresh environment with feectools
`1d8d47c` and the pinned cunumpy, after merging devel (with #774 and
#775). The PR passes `test_cuda_parity`, `test_cuda_emulation`,
`test_kernel_backends`, `test_sorting`, `test_accum_matrix_cupy`,
`test_preconditioner_cupy`, `test_poisson` and `test_output` on its own.
The top of the stack also passes the mass-matrix, preconditioner,
Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén,
post-processing, polar fake-CuPy and all `pic` tests (1477 passed), the
examples test for the two profiling cases, the sorting, Poisson and
fused-gradient tests under `mpirun -n 2`, and the device MPI sort on the
fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil
mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid,
periodic and Dirichlet, on 1 and 2 ranks.
**Not tested on a GPU here.** The CUDA kernels and the device paths need
a run on the cluster.

## Stack (merge in order)

0. struphy-hub/feectools#104 (feectools, into
`devel-tiny`)

| # | PR | base |
|---|---|---|
| 1 | #782 update feectools (device ghost exchange, single-reduction
PCG); pcg_sr solver option | `devel` |
| 2 | #783 host/device conversions in post-processing; math.sqrt in
Species | #782 |
| 3 | #784 CUDA mass-matrix assembly kernel kernel_3d_mat | #783 |
| 4 | #785 apply separable mass matrices as Kronecker products of 1D
banded matrices | #784 |
| 5 | #786 Poisson/diffusion solve with fewer passes over the vectors |
#785 |
| 6 | #787 marker rows prepared inside the push kernels | #786 |
| 7 | #788 chunked marker loading, row-based weight update, leaner MPI
sorting; static field in PushVxB **(this PR)** | #787 |
| 8 | #789 profiling cases Poisson cube and Vlasov slab (CPU node vs
GPU, GPU scaling) | #788 |

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
max-models added a commit that referenced this pull request Oct 27, 2026
… vs GPU, GPU scaling) (#789)

Part 8 of 8 of the split of #772 (`cuda-aware-mpi-fixes`) into stacked
PRs. **Requires struphy-hub/feectools#104 to be
merged into feectools `devel-tiny` first** (PR 1 bumps the submodule).

- Poisson `gaussian_cube`: `--steps` (repeated solves with the matrices
assembled once), `--solver pcg|pcg_sr`, `--gpu-timing` (one thread per
rank, CUDA-event device times per region), `--no-output`. Submit scripts
for 28 CPU ranks vs 1 GPU and for GPU scaling.
`examples/Poisson/sweep_poisson.py` runs several cases.
- Vlasov `homogeneous_slab`: particle push profiling case (16M markers
by default, `--test-run` for the examples test), with post-processing
and the same two submit scripts.
- `profiling/profiling_job.py`: launcher detection and job setup for
these cases.
- `profiling/sweep.py` (`run_sweep`, `variant_entries`): runs several
submit scripts as one sweep in one process (`profiling_job.begin_sweep`
/ `finalize_all`), so they share one packaging folder; a failing script
is reported and the sweep goes on. `sweep_poisson.py` imported it, but
it was never committed, so it is written new here. Checked with a dry
run of `sweep_poisson.py` (30 submit commands) and a run on test scripts
(variants, a failing exit code, an exception, registered cases).


## Tests

Local, macOS without a GPU, in a fresh environment with feectools
`1d8d47c` and the pinned cunumpy, after merging devel (with #774 and
#775). The PR passes `test_cuda_parity`, `test_cuda_emulation`,
`test_kernel_backends`, `test_sorting`, `test_accum_matrix_cupy`,
`test_preconditioner_cupy`, `test_poisson` and `test_output` on its own.
The top of the stack also passes the mass-matrix, preconditioner,
Derham-GPU, fused-gradient, Kronecker-block, Poisson, shear Alfvén,
post-processing, polar fake-CuPy and all `pic` tests (1477 passed), the
examples test for the two profiling cases, the sorting, Poisson and
fused-gradient tests under `mpirun -n 2`, and the device MPI sort on the
fake CuPy on 2 and 4 ranks. The Kronecker products match the stencil
mass matrices to 5e-16 for M0, M1, M2, M3, Mv, M1n and M2n on a Cuboid,
periodic and Dirichlet, on 1 and 2 ranks.
**Not tested on a GPU here.** The CUDA kernels and the device paths need
a run on the cluster.

## Stack (merge in order)

0. struphy-hub/feectools#104 (feectools, into
`devel-tiny`)

| # | PR | base |
|---|---|---|
| 1 | #782 update feectools (device ghost exchange, single-reduction
PCG); pcg_sr solver option | `devel` |
| 2 | #783 host/device conversions in post-processing; math.sqrt in
Species | #782 |
| 3 | #784 CUDA mass-matrix assembly kernel kernel_3d_mat | #783 |
| 4 | #785 apply separable mass matrices as Kronecker products of 1D
banded matrices | #784 |
| 5 | #786 Poisson/diffusion solve with fewer passes over the vectors |
#785 |
| 6 | #787 marker rows prepared inside the push kernels | #786 |
| 7 | #788 chunked marker loading, row-based weight update, leaner MPI
sorting; static field in PushVxB | #787 |
| 8 | #789 profiling cases Poisson cube and Vlasov slab (CPU node vs
GPU, GPU scaling) **(this PR)** | #788 |

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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