Auto tuning related limitations

Currently, there are only two auto-tuning related parameters for constructor of VirtualMultiArray. memMult and mem.

If memMult parameter is given output of benchmarking:

PcieBandwidthBenchmarker bench;

VirtualMultiArray<Obj> data(... bench.bestBandwidth(2),VirtualMultiArray<Obj>::MemMult::UseDefault);

it reduces combined capacity for the virtual array. Similarly, when optimized for maximum-capacity, the overall bandwidth drops. Even the default distribution (with last two parameters not given by user) does not handle any overflow/slow cases.

Virtual Array = 10 GB

Card                        pci-e bridge spec       maximized bandwidth         maximized capacity     default
GTX1080ti   11GB-vram       2.0 16x                 8GB                         8.5GB                  5GB
GT1030      2GB-vram        2.0 4x                  2GB (possible overflow!)    1.5GB                  5GB (error)
combined capacity                                   error                       10GB                   error

---

Virtual Array = 4 GB

Card                        pci-e bridge spec       maximized bandwidth         maximized capacity     default
GTX1080ti   11GB-vram       2.0 16x                 4GB/s                        3.3GB/s               1GB/s
GT1030      2GB-vram        2.0 4x                  1GB/s                        0.7GB/s               1GB/s (possible overflow!)
combined bandwidth                                  5GB/s                        4GB/s                 2GB/s