num_proc,niter
1,3.0
2,2.5
4,2.5
8,2.875
16,3.625
32,4.34375
64,4.78125
128,4.921875
256,4.85546875
512,4.66015625
1024,4.5791015625
2048,4.47412109375
4096,4.492919921875
