Engineering Roundtable I: Newisys’ HORUS Chipset

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Partitions

David Kanter:
Can a partition be made with non-integer resources (i.e. 2/3 of an I/O link, 1.5 MPUs, etc.)?

Rajesh Kota:
Could you please elaborate a bit more. What do you mean 2/3 of an I/O link?

David Kanter:
If you have say, RAID controllers through PCI-X using an I/O link in a quad, could you share the RAID controller between two partitions?

Rajesh Kota:
If you mean can we have transactions from two different partitions share one physical I/O link, then the answer would be no. The reason is that the partition is a concept supported by HORUS. An Opteron or any of the chipsets does not have a clue how to keep transactions from two separate partitions logically separate. I don’t think Newisys would go down the path of trying to use one physical link to support two partitions. We solve this in our system design by providing two I/O links in each box (see Figure 2 for an example).


Figure 2 – Hypothetical Example of Partitions using HORUS

The IO chains are connected using the ncHT links in the Opteron processors. The Opteron processors do not support partitions. Each transaction in the coherent and non-coherent domain is tagged with transaction IDs, which are used to maintain coherency, ordering, and a correct relationship between multiple packets for one transaction. In the system shown in Figure 2, it is possible to have two transactions in different partitions with the same transaction ID. HORUS knows about the partition and keeps them separate to prevent any problems. Opteron processors don’t know about it. Partitioning is a feature introduced on top of Opteron processors by HORUS. Hence we can’t send transaction from different partitions to the same Opteron processor.

David Kanter:
Do you see that as a future feature you might be able to add?

Rajesh Kota:
No.


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