[issue8299] Improve GIL in 2.7

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

> SHA1 hashing (C)
> 
> threads= 1:  1275 iterations/s. balance
> threads= 2:  1267 ( 99%)        0.7238
> threads= 3:  1271 ( 99%)        0.2405
> threads= 4:  1270 ( 99%)        0.1508
> 
> Using the forced "do_yield" helps balance things, but not much.  We
> still have a .7 balance in SHA1 hashing for two threads.

Which is not unreasonable, since SHA1 releases the GIL. The unbalance
would be produced by the Windows scheduler, not by Python.

Note: "do_yield" is not meant to "balance" things as much as to make
measurements meaningful at all. Without switching at all during say 2
seconds, the numbers become totally worthless.

> If no one objects, I'd like to submit this changed ccbench.py to the trunk.

Please let me take a look.

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