On Wed, Dec 19, 2007 at 07:17:21PM -0800, Ron Mayer wrote: > > but it doesn't follow that you will get > > 10X improvement with 10 threads, or even 4X with 4. > > Yeah - unless those 10 cores have additional I/O to the > memories compared to a 1 core system (which I'd hope > would be the case or else I'd expect many apps would be > run into memory bottlenecks on such systems, no?).
I don't suppose you saw the document from Ulrich Drepper "What Every Programmer Should Know About Memory". It's a fact that most machines with multiple cores have less L2 cache/core than a single core machines. And having multiple conduits to main memory isn't that common at all. So having more threads sometimes *decreases* performance because you cut the L2 cache and memory bandwidth in half. The document is very useful for getting tips about how to work out optimal thread/memory/datasize ratios. The way around this is a NUMA architecture, but that's a whole other ball of wax. Have a nice day, -- Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ > Those who make peaceful revolution impossible will make violent revolution > inevitable. > -- John F Kennedy
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