[petsc-dev] Question re parallel sparse Matrix-vector / KSP solvers

[David Henty]

I see in the example for how to solve A.x_i = b_i (ie multiple 
right-hand-sides for the same matrix), it simply loops over multiple 
separate KSP calls.

Wouldn't there be some benefit in having a matrix-vector routine that 
computed y_i = A.x_i for multiple "i" values? The parallel overhead 
comes from communicating the off-process x values. As this is probably 
latency dominated (especially as we go to many processes), the comms 
cost of doing the communications would rise quite slowly for additional 
vectors. Likewise, the cache utilisation of the sparse A matrix entries 
would be helped by doing sevefal multiplications at once.

Has this already been implemented, or maybe in the pipleline? Or am I 
somehow missing the point ...

Thanks!

David

-- 
Dr David Henty                        EPCC, The University of Edinburgh
HPC Training and Support              Edinburgh EH9 3JZ, UK
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