Advanced Micro Devices Inc (AMD)

[calbiker]

sgolds- welcome to the board! It has been a while since I've seen a RMBS proponent. That should help to liven things up here!

Thanks guys (and gals). If you want liven up your lives, you can always drop by on the other side.

Anyhow, I will have to disappoint your latency fantasy.

Sorry calbiker doesn't have any latency fantasies. They are indeed real. PCI Express as well as HT have latencies. As I understand it, Opteron first converts the data stream into serial packets per HT protocol. Then this data stream needs to be converted into a packet suitable for PCI Express. These packets are not identical. I don't believe HT uses 8b/10b encoding. Data coming from the PCI card need to make the same transformations. There is definitely more latency involved.

First of all, PCI-Express is an I/O fabric and HyperTransport is an interprocessor connect fabric. They are complimentary, they do not conflict.

Yes they are complimentary and do not conflict. But that's not the issue here. The problem is that Opteron has an integrated the memory controller. This is great for low latency memory/processor operations, but not for I/O systems. Opteron is pin restricted. It doesn't have a PCI Express bus. But it has a HT bus, which then must be converted into a PCI Express bus. This takes extra latency and is not efficient.

Second architectural point: AMD64 processors have an on-board memory controller, the memory does not have to touch HyperTransport at all. Very low latency. For multiprocessor configurations, some memory accesses are handled by a remote processor's memory controller over HT, very similar to traditional North Bridge access.

Yes, I agree with all that, but this isn't the issue.

In no case does memory ever touch PCI-Express. PCI-Express simply replaces the existing PCI connection.

Here's a good review if it.
http://www.xilinx.com/esp/networks_telecom/optical/collateral/pci_express.pdf

AMD has announced support of PCI-Express for I/O. It fits AMD's archtecture like a glove.

That's just it, I don't think it fits like a glove. Many of the PCI cards probably won't be affected by the higher latency. But what about the new PCI Express video cards? They may not work. Will Opteron require special video cards?