Bug in MPI planner for Nx1 transforms

[matteo-frigo]

[Bug report from Damon Farnsworth from Cray:]

While running the mpi checks on the stock fftw 3.3.4 (I also tested against version 3.3 and saw the same failure) with
your bench tester I came across a failure (relative error) for certain problems. It seems to be isolated (as far as
I’ve seen) to complex problems (single or double precision; inplace or out-of-place; forward or backward) of sizes Nx1
where N is roughly 25 or greater, although some values of N will pass. This seems to only happen when the number of
ranks is greater than one. I give a couple of examples below.

Here’s a successful test, one mpi rank:

aprun -n1 ./mpi-bench.double.static.exe -v2 --verify obc98x1

planner time: 0.005592 s

(mpi-dft-serial

(dft-ct-dit/7

(dftw-direct-7/24 "t1bv_7_avx")

(dft-direct-14-x7 "n1bv_14_avx")))

flops: 318 add, 162 mul, 156 fma

estimated cost: 792.000000, pcost = 0.000000

obc98x1 4.05599e-16 5.38317e-16 9.21329e-16

Here’s the same test but with two mpi ranks:

aprun -n2 ./mpi-bench.double.static.exe -v2 --verify obc98x1

planner time: 0.013054 s

(mpi-dft-rank1/2/last

(mpi-dft-rank1-bigvec/contig

(mpi-transpose-pairwise

  (null)

  (rdft-transpose-cut-2x25-x2

    (rdft-vrank>=1-x2/1

      (rdft-rank0-iter-ci/2-x23))

    (rdft-rank0-ip-sq/2-x2-x2))

  (null)

  (null))

(dft-direct-2-x25 "n2bv_2_sse2")

(mpi-transpose-pairwise

  (rdft-transpose-cut-25x2-x2

    (rdft-rank0-ip-sq/2-x2-x2)

    (rdft-rank0-iter-co/2-x23-x2))

  (rdft-nop)

  (rdft-nop)

  (null)))

(dft-ct-dit/7

(dftw-direct-7/12 "t1buv_7_sse2")

(dft-indirect-before

  (dft-direct-7-x7 "n1bv_7_avx")

  (dft-r2hc-1

    (rdft-rank0-ip-sq/2-x7-x7))))

(mpi-transpose-pairwise

(rdft-rank0-iter-co/2-x25-x2)

(rdft-nop)

(rdft-nop)

(null)))

flops: 430 add, 232 mul, 192 fma

estimated cost: 1933.283180, pcost = 8989.000000

Found relative error 1.030928e-02 (impulse 1)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.030928e-02 (impulse)

Found relative error 1.261234e-01 (time shift)

Found relative error 1.225574e-01 (time shift)

Found relative error 1.386730e-01 (time shift)

Found relative error 1.259797e-01 (time shift)

Found relative error 9.564516e-02 (time shift)

Found relative error 1.640549e-01 (time shift)

Found relative error 1.029969e-01 (time shift)

Found relative error 1.051039e-01 (time shift)

Found relative error 1.261746e-01 (time shift)

Found relative error 1.214751e-01 (time shift)

Found relative error 4.337277e-02 (freq shift)

Found relative error 4.390274e-02 (freq shift)

Found relative error 4.652282e-02 (freq shift)

Found relative error 5.435396e-02 (freq shift)

Found relative error 4.417120e-02 (freq shift)

Found relative error 4.410327e-02 (freq shift)

Found relative error 4.349692e-02 (freq shift)

Found relative error 4.195425e-02 (freq shift)

Found relative error 4.465815e-02 (freq shift)

Found relative error 3.965394e-02 (freq shift)

obc98x1 3.2374e-16 0.0103093 0.164055