[petsc-dev] Implementing longer pipelines with VecDotBegin and VecDotEnd

[Wim Vanroose]

Dear All,

We have a working prototype of pipe(l) CG in Petsc, where dot products are
taking multiple iterations to complete.  Due to the limitations of
VecDotBegin we had to used MPI_WAIT and MPI_Iallreduce.
A high level overview of the communication is given in the figure.   The
preprint of the paper is https://arxiv.org/abs/1801.04728

How should we proceed?  Can we contribute this routine to KSP while it uses
primitive MPI calls?
Or should we interact with petsc-dev to see if we can redesign  VecDotBegin
and VecDotEnd
to be able to handle these cases? And then rewrite the prototype with these
new calls?

Can we talk about this at SIAM PP18?

Wim Vanroose
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