[petsc-users] MemCpy (HtoD and DtoH) in Krylov solver

[Xiangdong]

Hello everyone,

I am new to petsc gpu and have a simple question.

When I tried to solve Ax=b where A is MATAIJCUSPARSE and b and x are
VECSEQCUDA  with GMRES(or GCR) and pcnone, I found that during each krylov
iteration, there are one call MemCpy(HtoD) and one call MemCpy(DtoH). Does
that mean the Krylov solve is not 100% on GPU and the solve still needs
some work from CPU? What are these MemCpys for during the each iteration?

Thank you.

Best,
Xiangdong
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