The Idea Behind AMD
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But this does force us to address the relationship between AMD’s hardware and the software that’ll invariably run on it. In
Intel Core i5 And Core i7: Intel’s Mainstream Magnum Opus, I brought up specific optimizations in Windows 7 that were the product of collaboration between Intel and Microsoft—notably, core parking. Windows 7 intelligently schedules to physical cores before utilizing logical (Hyper-Threaded) cores.
In theory, AMD could benefit from the same thing. If Windows were able to utilize an FX-8150’s four modules first, and then backfill each module’s second core, it’d maximize performance with up to four threads running concurrently. This isn’t the case, though. According to Arun Kishan, software design engineer at Microsoft, each module is currently detected as two cores that are scheduled equally.
So, in a dual-threaded application, you might see one active module and three idle modules—great for optimizing power, but theoretically less ideal from a performance standpoint. This also plays havoc with AMD’s claim that, when only one thread is active, it has full access to shared resources. Adding just one additional thread could tie up those shared resources, even as multiple other modules sit idle.
Microsoft is looking to change that behavior moving forward, though.
Arun says that the dual-core modules have performance characteristics more similar to SMT than physical cores, so the company is looking to detect and treat them the same as Hyper-Threading in the future. The implications there would be significant. Performance would unquestionably improve, while AMD’s efforts to spin down idle modules would be made less effective."