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The Managed Runtime Initiative

The Managed Runtime Initiative

Posted Sep 6, 2010 23:13 UTC (Mon) by nix (subscriber, #2304)
In reply to: The Managed Runtime Initiative by Blaisorblade
Parent article: The Managed Runtime Initiative

since Python uses standard reference counting, it is not efficient even in the short term view, because copying a pointer to the stack causes a heap mutation, even to pass a parameter to a procedure. That's why trying to support multithreading gave a 2x slowdown.
Oh no, there are much more appalling reasons why Python's multithreading is awful. The GIL acquisition macros were never designed with multiple CPUs in mind: on a one-thread-of-execution machine (what we used to call 'one CPU'), it all works fine, but if there's more than one, they race with each other and often end up bouncing ownership back and forth and both blocked for astounding periods of time. There's an awesome presentation on the subject, strongly recommended.


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The Managed Runtime Initiative

Posted Sep 10, 2010 21:07 UTC (Fri) by Blaisorblade (guest, #25465) [Link]

Ah, that's right, I even knew of that presentation (and watched it again). I kind-of guessed that people were working on that (without any evidence other than "somebody noticed"), and I had no idea about how to fix that.

Moreover, there was work (from Antoine Pitrou IIRC) to change the policies of the GIL - it was/is released/reacquired every 100 opcodes (which might be ridiculously small or too large, depending on the opcodes), while A. Pitrou wanted to have some saner scheduling.

Releasing it every timeslice (i.e. ~80/100 ms IIRC) would probably help with the problems of that presentation - I should have another look to know if this makes sense. A simple user-level scheduler for GIL acquisition would maybe be needed in the worst case, but hopefully not.


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