AMD 64 manual Synthetic Test, Internal Resources Associated with a Quartet Node

40555 Rev. 3.00 June 2006	Performance Guidelines for AMD Athlon™ 64 and AMD Opteron™
	ccNUMA Multiprocessor Systems

	C0
	C1
4 GV/s per direction	4 GV/s per direction
@ 2 GHz Data Rate	@ 2 GHz Data Rate

4 GV/s per direction @ 2 GHz Data Rate

HT = HyperTransport™ Technology

Figure 2. Internal Resources Associated with a Quartet Node

From the perspective of the MCT, a memory request may come from either the local core or from

another core over a coherent HyperTransport link. The former request is a local request, while the latter is a remote request. In the former case, the request could be routed from the local core to the

SRI, then to the XBar and then to the MCT. In the later case, the request is routed from the remote core over the coherent HyperTransport link to the XBar and from there to the MCT.

The MCT, the SRI and the XBar on each node all have internal buffers that are used to queue transaction packets for transmission. For additional details on the Northbridge buffer queues, refer to Section A.1 on page 39.

From a system perspective, the developer can think of the system as having three key resources that affect throughput: memory bandwidth, HyperTransport bandwidth and buffer queue capacity.

2.2Synthetic Test

The test used is a simple synthetic workload consisting of two threads with each thread accessing an array that is not shared with the other thread. The time taken by each thread to access this array is measured.

Each thread does a series of read-only or write-only accesses to successive elements of the array using a cache line stride (64 bytes). The test iterates through all permutations of read-read, read-write, write-read, and write-write for the access patterns of the two threads. Each array is sized at 64MB— significantly larger than the cache size.

This synthetic test is neither a pure memory latency test nor a pure memory bandwidth test; rather it places varying throughput and capacity demands on the resources of the system described in the previous section. This provides an understanding of how the system behaves when any of the

Chapter 2 Experimental Setup 15