On 9/14/07, Justin Tulloss <[EMAIL PROTECTED]> wrote: > > On 9/14/07, Adam Olsen <[EMAIL PROTECTED]> wrote: > > > Could be worth a try. A first step might be to just implement > > > the atomic refcounting, and run that single-threaded to see > > > if it has terribly bad effects on performance. > > > > I've done this experiment. It was about 12% on my box. Later, once I > > had everything else setup so I could run two threads simultaneously, I > > found much worse costs. All those literals become shared objects that > > create contention. > > It's hard to argue with cold hard facts when all we have is raw speculation. > What do you think of a model where there is a global "thread count" that > keeps track of how many threads reference an object? Then there are > thread-specific reference counters for each object. When a thread's refcount > goes to 0, it decrefs the object's thread count. If you did this right, > hopefully there would only be cache updates when you update the thread > count, which will only be when a thread first references an object and when > it last references an object. > > I mentioned this idea earlier and it's growing on me. Since you've actually > messed around with the code, do you think this would alleviate some of the > contention issues?
There would be some poor worst-case behaviour. In the case of literals you'd start referencing them when you call a function, then stop when the function returns. Same for any shared datastructure. I think caching/buffering refcounts in general holds promise though. My current approach uses a crude hash table as a cache and only flushes when there's a collision or when the tracing GC starts up. So far I've only got about 50% of the normal performance, but that's with 90% or more scalability, and I'm hoping to keep improving it. -- Adam Olsen, aka Rhamphoryncus _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
