推 tsairay:樓上的各位,USB在傳輸的時候是要吃CPU資源的,會變慢是因為 09/20 09:29
→ tsairay:這樣,你們focus在錯誤的地方了... 09/20 09:30
→ visor:樓上肯定沒聽過 DMA ... 09/20 10:46
推 tsairay:不要把x86的知識套用在ps3上,有DMA那也要他們有做 09/20 10:48
→ visor:..... 誰說只有 x86 有 DMA..... 09/20 10:49
推 tsairay:DMA又不是USB的標準,要有加進去才有,沒加就是沒有 09/20 10:51
推 flygaga:等到破解後再試試看能不能跑..不就好了@@ 09/20 10:59
→ cassine:有人總是喜歡潑冷水護航，自己又不參與破解別人吃麵他喊熱 09/20 11:01
→ visor:我看過 linux for ps3 的 usb driver 是有支援 DMA 的 09/20 11:05
→ visor:所以 ps3 的 usb 基本上是支援 DMA 的 09/20 11:05
推 cassine:娃！某樓又被打臉了:P 09/20 11:10
→ visor:我玩過一堆非x86的開發版，至少還沒看到不支援 DMA 的 USB 09/20 11:13
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.
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.
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).
============================================================================
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
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※ 編輯: tsairay 來自: 220.130.46.98 (09/20 14:00)
推 monHHH:專業推 09/20 14:42
推 nightk:專業推 09/20 16:34
→ SUCKERKING:USB 2.0實際傳輸速度不如理論基本上跟CPU沒有關係， 09/20 23:30
→ SUCKERKING:翻翻spec就知道overhead在哪些地方。 09/20 23:31
→ JackONeilll:的確 網路也是如此 科科 09/20 23:54
→ todotaurus:我想問一個無關緊要的問題，就是為什麼USB2.0做不到理 09/21 01:55
→ todotaurus:論值，卻不做好，然後弄一個USB3.0的規格出來呢!? 09/21 01:56
→ todotaurus:對不起，由於看到了一堆USB速度的討論串，所以就生出莫 09/21 01:57
→ todotaurus:明的疑問...不過好像跟這版沒關係@@~ 我左轉出去好了 09/21 01:57
推 MAGICXX:因為各種誤差 連接處不是100%完全連接之類的系統誤差 09/21 01:59
→ MAGICXX:而且大部分的理論環境在地球上都找不到 09/21 02:00
→ MAGICXX:EX:0重力 0摩擦力 絕對低溫 等等 這些只有腦補補的出來 09/21 02:01
→ MAGICXX:現實社會中是做不到的 這是坐實驗藥有的觀念Q_Q 09/21 02:01
→ JackONeilll:就像三樓說的 理論值講的是毛頻寬 實際值講的是淨頻寬 09/21 03:00
→ JackONeilll:沒有做不到 就像開高速公路你不可能車頭接車尾吧? 09/21 03:02
→ JackONeilll:行車間距就是那個overhead 真想了解就去google 09/21 03:05
→ narcissusli:有疑惑的話,就去看USB spec..知道packet運作就能理解, 09/21 03:59
→ narcissusli:為何跑不到理論值.封包傳送總會有槓龜,需要重送的時候 09/21 04:00