> From: Christopher Schultz [mailto:ch...@christopherschultz.net] > Subject: Re: [OT] IIS7/isapi/tomcat performance
> The question I have is how does the bus controller know > that there are multiple 32-bit values coming down the line, > and that it can send them simultaneously down the bus? A traditional "bus controller" hasn't been used in quite some time, and buses themselves are rapidly being replaced by point-to-point connections (finally), at least in terms of CPUs accessing memory. The interface between the L1 operand cache and the multiple ALUs is under control of a scheduler that's aware of the possible 72 simultaneous loads and stores going on, so it can combine accesses as it sees fit. Accesses between lower-level caches and actual RAM have always been wider than the data path within a core. > There's more data to be sent over the bus than just pointers > to other pieces of data. Of course - except there is no "the bus". > You have to move the instruction itself Not these days. The instruction will be loaded from memory once, broken (and combined) into micro-ops, and those are stored in the instruction cache. If you're getting i-cache much beyond single digit percentages, your performance will be horrible. > so there's lots of opportunities for other data > to get in the way of this "DRR-style" data transfer > across the bus. Your continued use of the phrase "the bus" is rather quaint... > that would only affect the processing of, say, a 64-bit pointer > within the core... No, it affects all data, not just pointers. > I'd love to see some real documentation and/or testing on this > type of stuff. http://www.intel.com/products/processor/manuals/ Start with this one: http://www.intel.com/Assets/PDF/manual/253665.pdf > my intuition tells me that the CPU and bus aren't magic :) Compared to just a few years ago, they are. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers.
