Multiprocessing: Difference between revisions
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From the operating system's perspective, SMT looks a lot like SMP, except for performance characteristics. For SMT a single physical CPU executes multiple "threads" (or logical CPUs), and the performance of one thread/logical CPU is effected by work done by other threads/logical CPUs in the same physical CPU/core (as the physical CPU's resources are shared). |
From the operating system's perspective, SMT looks a lot like SMP, except for performance characteristics. For SMT a single physical CPU executes multiple "threads" (or logical CPUs), and the performance of one thread/logical CPU is effected by work done by other threads/logical CPUs in the same physical CPU/core (as the physical CPU's resources are shared). |
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For the 80x86 architecture, Intel |
For the 80x86 architecture, Intel was the first manufacturer to implement SMT (called "hyperthreading" by Intel). When Intel first introduced hyperthreading it got some negative publicity due to performance problems; partly caused by the way it was implemented and partly because a lot of software wasn't designed for it (single-threaded) and operating system schedulers weren't optimized for it. Intel stopped using SMT/hyper-threading for a while; but since then software has caught up and later CPUs (Atom, Core i7) show significant performance improvements from SMT (up to about 30% performance improvement on multi-threaded loads). AMD's Ryzen platform, released in 2017, introduced SMT to a non-Intel CPU for the first time. |
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== AMP (Asymmetric Multiprocessing) == |
== AMP (Asymmetric Multiprocessing) == |
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