Make perf_monitoring/gemm script more flexible:   - skip existing dataset   - add a "-up" option to recompute the dataset (see script header)   - allow to specify a filename prefix
Make perf_monitoring/gemm script more flexible:
  - skip existing dataset
  - add a "-up" option to recompute the dataset (see script header)
  - allow to specify a filename prefix

pthulhu/eigen,pthulhu/eigen,pthulhu/eigen,pthulhu/eigen,pthulhu/eigen