On 14/12/2021 19.19, Eric Snow wrote:
A while back I concluded that neither approach would work for us. The
approach I had taken would have significant cache performance
penalties in a per-interpreter GIL world. The approach that modifies
Py_INCREF() has a significant performance penalty due to the extra
branch on such a frequent operation.
Would it be possible to write the Py_INCREF() and Py_DECREF() macros in
a way that does not depend on branching? For example we could use the
highest bit of the ref count as an immutable indicator and do something like
ob_refcnt += !(ob_refcnt >> 63)
instead of
ob_refcnt++
The code performs "ob_refcnt += 1" when the highest bit is not set and
"ob_refcnt += 1" when the bit is set. I have neither tested if the
approach actually works nor it's performance.
Christian
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