On Tue, 2005-09-20 at 22:43, Guido van Rossum wrote: > On 9/20/05, John J Lee <[EMAIL PROTECTED]> wrote: [...] > I don't know that any chips are designed with threading in mind. Fast > threading benefits from fast context switches which benefits from > small register sets. I believe the trend is towards ever large > register sets. Also, multiple processors with shared memory don't > scall all that well; multiple processors with explicit IPC channels > scale much better. All arguments for multi-processing and against > multi-threading.
Exactly! I believe the latest MP opteron chipsets use hypertransport busses to directly access the other processor's memory and possibly CPU cache. In theory this means shared memory will not hurt too badly, helping threading. However, memory contention bottlenecks and cache coherency will always mean shared memory hurts more, and will never scale better, than IPC. The reality is threads were invented as a low overhead way of easily implementing concurrent applications... ON A SINGLE PROCESSOR. Taking into account threading's limitations and objectives, Python's GIL is the best way to support threads. When hardware (seriously) moves to multiple processors, other concurrency models will start to shine. In the short term there will be various hacks to try and make the existing plethora of threading applications run better on multiple processors, but ultimately the overheads of shared memory will force serious multi-processing to use IPC channels. If you want serious MP, use processes, not threads. I see anti-GIL threads again and again. Get over it... the GIL rocks for threads :-) -- Donovan Baarda <[EMAIL PROTECTED]> _______________________________________________ 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
