[petsc-users] Question about petsc4py with cuda

[MIA]

Hi,

I am trying to solve a large linear equation, which needs a GPU solver as comparison. I install a CUDA-enabled PETSc and petsc4py from sources using the release tarball. According to the test results after installation, the PETSc can successfully work with cuda. 

All my programs are written in python, so I turn to petsc4py. But I do not find any commands that define variables on coda device or define where the direct solver is executed. I check `nvidia-smi` and find my cuda does not work at all when executing my python script:

from petsc4py import PETSc
import numpy as np

n = 1000

nnz = 3 * np.ones(n, dtype=np.int32)
nnz[0] = nnz[-1] = 2

A = PETSc.Mat()
A.createAIJ([n, n], nnz=nnz)

# First set the first row
A.setValue(0, 0, 2)
A.setValue(0, 1, -1)
# Now we fill the last row
A.setValue(999, 998, -1)
A.setValue(999, 999, 2)

# And now everything else
for index in range(1, n - 1):
    A.setValue(index, index - 1, -1)
    A.setValue(index, index, 2)
    A.setValue(index, index + 1, -1)   
    
A.assemble()

indexptr, indices, data = A.getValuesCSR()
b = A.createVecLeft()
b.array[:] = 1
for i in range(10):
    ksp = PETSc.KSP().create()
    ksp.setOperators(A)
    ksp.setType('preonly')
    ksp.setConvergenceHistory()
    ksp.getPC().setType('lu')
    x = A.createVecRight()
    ksp.solve(2*b, x)
    residual = A * x - 2*b
    if i % 10 == 0:
        print(f"The relative residual is: {residual.norm() / b.norm()}.”)

What should I do to utlize GPU to execute the KSP task? Are there some settings to be modified?

Looking forward to your early reply. Thanks a lot.