Code stalls and resumes on KNL at cambridge. Curious.
CG iterations 23ms each, then 3200 ms pauses. Mean bandwidth reports
as 200MB/s. Comms dominant in the report. However, the time behaviour suggests it
is *bursty*.... Could be swap to disk?
gives 8x (!) speed up on Haswell laptop vs. standard CG for 8 RHS solves.
166 iterations vs. 537 iterations so algorithmic gain + 2x in flop rate gain.
Better than a slap in the face with a wet kipper.
