Here is the Nth patch for a globals/builtins cache. As other caches at the same kind, it shows very small to no gain on non-micro benchmarks, showing that contrary to popular belief, globals/builtins lookup are not a major roadblock in today's Python performance.

However, this patch could be useful in combination with other optimizations such as issue10399.  Indeed, using the globals/builtins version id, it is easy and very cheap to detect whether the function pointed to by a global name has changed or not.

As for micro-benchmarks, they show that there is indeed a good improvement on builtins lookups:

$ ./python -m timeit "x=len;x=len;x=len;x=len;x=len;x=len;x=len;x=len;x=len;x=len;"
-> without patch:
1000000 loops, best of 3: 0.282 usec per loop
-> with patch:
10000000 loops, best of 3: 0.183 usec per loop