Output on my x86_64 laptop:
- Ubuntu 18.04.3 LTS
- Core i7-8550U CPU @1.80 GHz (turbo boost/frequency scaling disabled)
- Results of best run using nice -20

Base
Function Call    :    2796349, 2.79635
Simple Loop      :     557062, 0.55706
Longjmp
Stack Switching  :    5602146, 5.60215
Full Continuation:   14935945, 14.93594
Jump Continuation:   33523215, 33.52322
Boost
FContext Fast    :    9517573, 9.51757
FContext Clean   :   11006061, 11.00606
FContext CallCC  :   18661906, 18.66191
Custom
Custom Fast Call :    7860666, 7.86067


Used stack size about 32 bytes.