Hi Jose, >> Since I just stumbled over VecMDot_SeqCUSP() when interfacing ViennaCL: Do >> you know what was the reason why the 'old' version was replaced by this >> expensive call to gemv() including the creation of temporaries, etc.? Just >> writing a custom kernel with one work group per dot-product should do the >> job perfectly, shouldn't it? > > My fault: > https://bitbucket.org/petsc/petsc-hg/commits/ec7a7de2acd477e5edd24cc5a3af441ce7a68a36 > > The motivation was that the previous version was even worse for me (VecMDot > is used a lot in SLEPc and GPU performance was really bad). At that time I > did not have the time to write a custom kernel. If you write one, I could > help in testing and measuring performance.
Thanks for providing the context. It makes sense to me now, because for eigenvalue computations you typically have a lot more vectors taking part in mdot as compared to GMRES. This looks like an archetypal example for using two different kernels: The first is suitable for 'small' numbers of vectors (GMRES), while the second is more gemv-like and good for larger vector counts (SLEPc). I'll let you know as soon as it's ready for testing. Thanks and best regards, Karli
