AMD ATHLON 64 - Manual (Page 21)

Chapter 3 Analysis and Recommendations 21
Performance Guidelines for AMD Athlon™ 64 and AMD Opteron™
ccNUMA Multiprocessor Systems
40555 Rev. 3.00 June 2006
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.
Figure 4. Read-Only Thread Running on Node 0, Accessing Data from 0, 1 and 2
Hops Away on an Idle System
Time for read
100%
108% 109%
130%
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0.0.r.0 0.0.r.1 0.0.r.2 0.0.r.3
0 Hop 1 Hop 1 Hop 2 Hop