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Single instruction, multiple thread (SIMT) is a parallel execution model, used in some GPGPU platforms, where multithreading is simulated by SIMD processors. The processors, say a number of them, seem to execute many more than tasks. This is achieved by each processor having multiple "threads" (or "work-items"), which execute in lock-step, and are analogous to SIMD "lanes". SIMT was introduced by Nvidia: SIMT is intended to limit instruction fetching overhead, and is used in modern GPUs (including, but not limited to those of Nvidia and AMD) in combination with 'latency hiding' to enable high-performance execution despite considerable latency in memory-access operations. This is where the processor is oversubscribed with computation tasks, and is able to quickly switch between tasks when it would otherwise have to wait on memory. This strategy is comparable to multithreading in CPUs (not to be confused with multi-core). A downside of SIMT execution is the fact that thread-specific control-flow is performed using "masking", leading to poor utilisation where a processor's threads follow different control-flow paths. For instance, to handle an ''if''-''else'' block where various threads of a processor execute different paths, all threads must actually process both paths (as all threads of a processor always execute in lock-step), but masking is used to disable and enable the various threads as appropriate. Masking is avoided when control flow is coherent for the threads of a processor, i.e. they all follow the same path of execution. The masking strategy is what distinguishes SIMT from ordinary SIMD, and has the benefit of inexpensive synchronization between the threads of a processor. == See also == * General-purpose computing on graphics processing units 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Single instruction, multiple threads」の詳細全文を読む スポンサード リンク
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