Re: [PS3 ] 關於PS3改機的問題

看板Modchip (改機)作者visor (~~~~~~~~~~)時間14年前 (2010/09/20 15:29)推噓6(6推 0噓 6→)

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※ 引述《tsairay (火の紅寶石)》之銘言： : http://moss.csc.ncsu.edu/~mueller/cluster/ps3/doc/LinuxKernelOverview.html : 看來看去就只有NIC有獨立的DMAC,所以能有背景下載 : 前景遊戲照玩的功能 : Giga Bit Ethernet(GbE) (Module name: gelic_net) : PS3 has built-in giga bit ethernet controller. Unlike conventional PC’s : ethernet controllers, it is not PCI device. It is connected to companion : chip directly. To access or setup the chip, guest OSes should use dedicated : hypervisor call. This controller has its dedicated DMA controller, : thus transfer data is automatically sent/received without PPE interventions. : There is also dedicated hypervisor call to set up DMAC. : 而USB host controller是直接被PPE access的 : USB : PS3 equips industry standard USB EHCI host controller and its companion : OHCI host controllers. Although most USB host controllers are PCI devices, : PS3 USB host controller exists in the companion chip. The PCI probe routines : of Linux are modified so that PS3 USB host controller can imitate PCI device. : After initialization, all operational registers of USB host controllers are : directly accessed by PPE, so no modification to original Linux USB host : controller driver is needed. PS3 has internal high speed USB hub. 以上這段只說明 PS3 的 usb host controller 是模擬成 PCI device 並沒說明他不支援 DMA，而你高亮度的地方也只說明 CPU 可直接操作 usb host controller 的 operational registers，這裡也沒說明 PCI device 的 data 是怎麼傳送的，CPU 直接存取 PCI device 的暫存器並不能代表沒使用 DMA。 : 至於visor說的DMA,我想指的是這個 : http://en.wikipedia.org/wiki/Cell_%28microprocessor%29 : the Cell processor marries the SPEs and the PPE via EIB to give access, : via fully cache coherent DMA (direct memory access), to both main memory : and to other external data storage.To make the best of EIB, and to overlap : computation and data transfer, each of the nine processing elements : (PPE and SPEs) is equipped with a DMA engine. 這邊有說明啦 PPC 有一個內建的 DMA engine 了，至於他有沒有用他去存取 USB，我是有看到 linux for ps3 裡的 usb driver 有啟動 DMA 機制，我還沒看到其他資料有說他是用 PPE 直接讀取 usb 的 data，至於 PS3 的 OS 我更無法得知了。 : 而這個DMA engine的目的不是為了降低在I/O時CPU的負擔 : 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). 以上你的講法會讓懂 DMA 的人笑死..... : ============================================================================ : 綜合以上幾點,可以證明PS3的USB傳輸是會耗用CPU資源的 : 想不耗用資源就只能像NIC那樣多加一個DMAC 不管怎樣，讀取 USB 一定會耗用 CPU 資源，畢竟 CPU 一定要下指令要 USB host controller 去讀取哪個裝置上的資料，但是到了資料傳輸時，就可以省去 CPU 的時間轉交由 DMAC 幫你讀取然後將資料轉存到 DRAM 上，DMA主要是不讓 CPU 去等待 device 回應的時間然後可以做其他事情，也可以減少 CPU 從 device 讀資料出來再寫回記憶體的指令數量，並不是什麼用 CPU 去加速 I/O.... -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 114.36.217.198 ※ 編輯: visor 來自: 114.36.217.198 (09/20 15:31)