Autotuning tile sizes for pluto optimisation

[NathanYukai]

Using script set different tile sizes and invoke with pluto, compare the performance.

[ggorman]

Googling for terms such as "tune tile size finite difference" will give you many examples such as http://www.vecpar.org/iwapt/iwapt2014_submission_1.pdf which gives you an idea of where we are going with this.

@marcoscimatec @felippezacarias - once this lands can you do a parameter sweep on your Xeons and Phi to find the best size or even a plot such as referenced above.