Tracer: Multithreading

[akva2]

Opening early to have somewhere to put markdown tables. Not ready for review/merge/whatever.

[akva2]

Timings for NORNE_ATW2013 [5 runs]

Revision	tracerAdvance	tracerAssemble	tracerPost	tracerSolve	tracerUpdate	Pre/post step
master	33.19 +- 0.32	26.80 +- 0.30	0.83 +- 0.00	5.45 +- 0.00	0.99 +- 0.00	55.19 +- 0.54
tracer_mt_solve	31.44 +- 0.04	26.91 +- 0.04	0.79 +- 0.00	3.63 +- 0.00	0.99 +- 0.00	54.07 +- 0.03
tracer_mt_assemble	27.85 +- 1.25	19.17 +- 1.32	2.07 +- 0.01	6.48 +- 0.00	1.00 +- 0.00	50.24 +- 1.24
tracer_mt_update	32.70 +- 0.12	26.39 +- 0.13	0.82 +- 0.00	5.39 +- 0.00	1.13 +- 0.00	54.96 +- 0.13
tracer_mt	24.62 +- 0.40	18.80 +- 0.33	1.15 +- 0.00	4.55 +- 0.00	1.10 +- 0.00	46.68 +- 0.48

[bska]

Not ready for review/merge/whatever.

Understood. The early performance improvements are nevertheless encouraging.

[atgeirr]

Understood. The early performance improvements are nevertheless encouraging.

At least for tracerAssemble. Wonder why the update part (although small) degraded, and why seemingly the mt for assemble has a negative effect on solve. All has been run with max 2 OpenMP threads?

[akva2]

don't look at the noise....

it's likely because things are not compute dominated but bandwidth dominated and whatever else i'm doing on my pc affects that even though the computations have their own cores. in particular update is basically shuffling data around, no computations going on there.