AMD 64 manual Chapter, Analysis and Recommendations, 2 Hop, 100%, 108%, 109%

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

distance. If they are indirectly connected to each other in a 4P configuration, it is considered as a 2 hop access distance.

The following example—extracted from mining the results of the synthetic test case—substantiates the recommendation to keep data local.

In this test, a single thread ran on node 0 (core 0) on an otherwise idle system and each of the following cases were measured and compared:

•Thread accessed data locally from node 0

•Thread accessed data one hop away from node 1

•Thread accessed data one hop away from node 2

•Thread accessed data two hops away from node 3

As seen in Figure 4 and Figure 5 on page 22, as the hop distance increases, access times increase for both reads and writes.

Time for read

1.8
1.6
1.4					130%
1.2	100%		108%	109%
1
0.8	0 Hop	1 Hop		1 Hop	2 Hop
0.6
0.4
0.2
0
	0.0.r.0		0.0.r.1	0.0.r.2	0.0.r.3

Figure 4. Read-Only Thread Running on Node 0, Accessing Data from 0, 1 and 2 Hops Away on an Idle System

Chapter 3 Analysis and Recommendations 21