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Memory model and instruction set architecture are orthogonal. Registers are entirely internal to a processor. They don't have to be replicated or consistent be

Memory model and instruction set architecture are orthogonal. Registers are entirely internal to a processor. They don't have to be replicated or consistent between different cores. Memory is shared system state. To write correct parallel programs, CPUs need to define how they manage consistency between different processors. x86 does have a more conservative model with stronger consistency than ARM, and this does have (theoretical) scaling consequences-- but Intel has a huge amount of experience making it fast.

artagnon 13y ago
The OP was clearly talking about memory barriers in architectures, not memory models in multi-threaded programming. Don't nitpick. > Memory is shared system state. To write correct parallel programs, CPUs need to define how they manage consistency between different processors. x86 does have a more conservative model with stronger consistency than ARM, and this does have (theoretical) scaling consequences-- but Intel has a huge amount of experience making it fast. Yeah, but what worries me is not raw throughput scaling; it's power consumption. The mainstream netbooks today: Macbook Air Mid-2012, Chromebook Pixel, and Lenovo X1 Carbon all use the 17W i5-3427U. The MBA Mid-2013 jumped to Haswell early and uses the 15W Core i5-4250U. But we still haven't been able to make a decent quad-core netbook: there's a 15W Core i7-4650U; I believe you can get an MBA 2013 with this as well, but a paltry 1.7 Ghz? How many years has it been since quad-cores first came out? It looks to me like x86 has stagnated: it doesn't matter how competent Intel is; the architecture seems to have fundamental problems. Now, I don't fully understand what the ARM A57 is, but the specs look really impressive [1]. Moreover, AMD has confirmed that they will manufacture Opterons in Q1 2014 [2]. I'm not completely sold on ARM or anything, but there is certainly something interesting going on: and we must investigate. [1]: http://www.arm.com/products/processors/cortex-a50/cortex-a57-processor.php http://www.arm.com/products/processors/cortex-a50/cortex-a57... [2]: http://www.amd.com/us/press-releases/Pages/amd-unveils-2013june18.aspx http://www.amd.com/us/press-releases/Pages/amd-unveils-2013j...

artagnon 13y ago

The OP was clearly talking about memory barriers in architectures, not memory models in multi-threaded programming. Don't nitpick. > Memory is shared system state. To write correct parallel programs, CPUs need to define how they manage consistency between different processors. x86 does have a more conservative model with stronger consistency than ARM, and this does have (theoretical) scaling consequences-- but Intel has a huge amount of experience making it fast. Yeah, but what worries me is not raw throughput scaling; it's power consumption. The mainstream netbooks today: Macbook Air Mid-2012, Chromebook Pixel, and Lenovo X1 Carbon all use the 17W i5-3427U. The MBA Mid-2013 jumped to Haswell early and uses the 15W Core i5-4250U. But we still haven't been able to make a decent quad-core netbook: there's a 15W Core i7-4650U; I believe you can get an MBA 2013 with this as well, but a paltry 1.7 Ghz? How many years has it been since quad-cores first came out? It looks to me like x86 has stagnated: it doesn't matter how competent Intel is; the architecture seems to have fundamental problems. Now, I don't fully understand what the ARM A57 is, but the specs look really impressive [1]. Moreover, AMD has confirmed that they will manufacture Opterons in Q1 2014 [2]. I'm not completely sold on ARM or anything, but there is certainly something interesting going on: and we must investigate. [1]: http://www.arm.com/products/processors/cortex-a50/cortex-a57-processor.php http://www.arm.com/products/processors/cortex-a50/cortex-a57... [2]: http://www.amd.com/us/press-releases/Pages/amd-unveils-2013june18.aspx http://www.amd.com/us/press-releases/Pages/amd-unveils-2013j...