※ 引述《visor (~~~~~~~~~~)》之铭言： : ※ 引述《tsairay (火の红宝石)》之铭言： : : 而这个DMA engine的目的不是为了降低在I/O时CPU的负担 : : 而是用CPU去加速I/O : : http://en.wikipedia.org/wiki/Direct_memory_access : : DMA engine : : In addition to hardware interaction, DMA can also be used to offload : : expensive memory operations, such as large copies or scatter-gather : : operations, from the CPU to a dedicated DMA engine. Intel includes such : : engines on high-end servers, called I/O Acceleration Technology (IOAT). : 以上你的讲法会让懂 DMA 的人笑死..... : : ============================================================================ : : 综合以上几点,可以证明PS3的USB传输是会耗用CPU资源的 : : 想不耗用资源就只能像NIC那样多加一个DMAC : 不管怎样，读取 USB 一定会耗用 CPU 资源，毕竟 CPU 一定要下指令要 USB host : controller 去读取哪个装置上的资料，但是到了资料传输时，就可以省去 CPU 的时间 : 转交由 DMAC 帮你读取然後将资料转存到 DRAM 上，DMA主要是不让 CPU 去等待 device : 回应的时间然後可以做其他事情，也可以减少 CPU 从 device 读资料出来再写回记忆体的 : 指令数量，并不是什麽用 CPU 去加速 I/O.... http://en.wikipedia.org/wiki/Direct_memory_access DMA-engine本来就是拿来做I/O加速的,跟用来降低CPU loading的DMA controller 完全是两种不同的应用,我想你需要仔细的分辨一下两者的不同 DMA engine In addition to hardware interaction, DMA can also be used to offload expensive memory operations, such as large copies or scatter-gather operations, from the CPU to a dedicated DMA engine. Intel includes such engines on high-end servers, called I/O Acceleration Technology (IOAT). IO Accelerator in Xeon As an example of DMA engine incorporated in a general-purpose CPU, newer Intel Xeon chipsets include a DMA engine technology called I/O Acceleration Technology (I/OAT), meant to improve network performance on high-throughput network interfaces, in particular gigabit Ethernet and faster. However, various benchmarks with this approach by Intel's Linux kernel developer Andrew Grover indicate no more than 10% improvement in CPU utilization with receiving workloads, and no improvement when transmitting data. --

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