AMD 64 manual Hop

Page 26

Performance Guidelines for AMD Athlon™ 64 and AMD Opteron™

40555 Rev. 3.00 June 2006

ccNUMA Multiprocessor Systems

 

•Threads firing at each other (crossfire)

The first thread runs on node 0 and writes to memory on node 1 (1 hop). The second thread runs on node 1 and writes to memory on node 0 (1 hop).

In each case, the two threads are run on core 0 of whichever code they are running on. The system is left idle except for the two threads. As shown in Figure 6 on page 26, the crossfire 1 hop-1 hop case is the worst performer.

Total Time for both threads (write-write)

2.2

2

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

149%

 

 

 

 

130%

 

 

 

 

 

 

 

 

113%

 

 

 

 

1 Hop

1 Hop

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0 Hop

1 Hop

 

 

 

1 Hop

 

 

 

 

 

 

0 Hop

NO

Xfire

 

 

 

 

 

 

 

Xfire

 

 

 

 

 

 

 

 

 

 

 

 

 

0.0.w.0 1.0.w.1 (0 Hops) (0 Hops)

0.0.w.1 1.0.w.3 (1 Hops) (1 Hops)

0.0.w.1 1.0.w.0 (1 Hops) (1 Hops)

Figure 6. Crossfire 1 Hop-1 Hop Case vs No Crossfire 1 Hop-1 Hop Case on an Idle System

When the write-only threads fire at each other (crossfire), the bidirectional HyperTransport link between node 0 and node 1 is saturated and loaded at 3.5 GB/s in each direction. The theoretical maximum bandwidth of the HyperTransport link is 4 GB/s in each direction. Thus, the utilization of the bidirectional HyperTransport link is 87% (3.5 ÷ 4) in each direction on that HyperTransport link.

On the other hand, when the write-only threads do not fire at each other (no crossfire), the utilization of the bidirectional link from node 0 to node 1 is at 60% in each direction. In addition, the utilization of the bidirectional link from node 1 to node 3 is at 54% in each direction. Since the load is now spread over two bidirectional HyperTransport links instead of one, the performance is better.

The saturation of these coherent HyperTransport links is responsible for the poor performance for the crossfire case compared to the no crossfire case. For detailed analysis, refer to Section A.2 on page 40.

In this synthetic test, read-only threads do not result in poor performance. Throughput of such threads is not high enough to exhaust the HyperTransport link resources. When both threads are read-only, the crossfire case is equivalent in performance to the no crossfire case.

It is also useful to study whether this observation holds on a system that is not idle. The following analysis explores the behavior of the two foreground threads under a variable background load.

26

Analysis and Recommendations

Chapter 3

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Contents Application Note Advanced Micro Devices, Inc. All rights reserved Contents Performance Guidelines for AMD Athlon 64 and AMD Opteron List of Figures List of FiguresList of Figures Revision History Revision HistoryRevision History Introduction Chapter IntroductionRelated Documents Chapter Introduction Introduction System Used Experimental SetupChapter Experimental Setup Quartet Topology Synthetic Test Internal Resources Associated with a Quartet NodeData Access Rate Qualifiers Reading and Interpreting Test Graphs Axis DisplayLabels Used Multiple Threads-Independent Data Analysis and RecommendationsScheduling Threads Chapter Analysis and RecommendationsScheduling on a Non-Idle System Data Locality ConsiderationsMultiple Threads-Shared Data Hop Keeping Data Local by Virtue of first Touch Chapter Analysis and Recommendations Analysis and Recommendations Common Hop Myths Debunked Threads access local dataAvoid Cache Line Sharing Myth All Equal Hop Cases Take Equal TimeHop Hop Hop Myth Greater Hop Distance Always Means Slower Time 102% 108% 107% 147% 126% 125% 136% 145% 136% 127% 126% 146% 129% 139% Locks Performance Guidelines for AMD Athlon 64 and AMD Opteron Analysis and Recommendations Conclusions Chapter ConclusionsConclusions Appendix a Appendix aDescription of the Buffer Queues Appendix a What Role Do Buffers Play in the Throughput Observed? Performance Guidelines for AMD Athlon 64 and AMD Opteron Appendix a Support Under Linux Controlling Process and Thread AffinitySupport under Solaris Support under Microsoft WindowsMicrosoft Windows does not offer node interleaving Node Interleaving Configuration in the Bios CcNUMA Multiprocessor Systems Appendix a
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64 specifications

AMD64 is a 64-bit architecture developed by Advanced Micro Devices (AMD) as an extension of the x86 architecture. Introduced in the early 2000s, it aimed to offer enhanced performance and capabilities to powering modern computing systems. One of the main features of AMD64 is its ability to address a significantly larger amount of memory compared to its 32-bit predecessors. While the old x86 architecture was limited to 4 GB of RAM, AMD64 can theoretically support up to 16 exabytes of memory, making it ideal for applications requiring large datasets, such as scientific computing and complex simulations.

Another key characteristic of AMD64 is its support for backward compatibility. This means that it can run existing 32-bit applications seamlessly, allowing users to upgrade their hardware without losing access to their existing software libraries. This backward compatibility is achieved through a mode known as Compatibility Mode, enabling users to benefit from both newer 64-bit applications and older 32-bit applications.

AMD64 also incorporates several advanced technologies to optimize performance. One such technology is the support for multiple cores and simultaneous multithreading (SMT). This allows processors to handle multiple threads concurrently, improving overall performance, especially in multi-tasking and multi-threaded applications. With the rise of multi-core processors, AMD64 has gained traction in both consumer and enterprise markets, providing users with an efficient computing experience.

Additionally, AMD64 supports advanced vector extensions (AVX), which enhance the capability of processors to perform single instruction, multiple data (SIMD) operations. This is particularly beneficial for tasks such as video encoding, scientific simulations, and cryptography, allowing these processes to be executed much faster, thereby increasing overall throughput.

Security features are also integrated within AMD64 architecture. Technologies like AMD Secure Execution and Secure Memory Encryption help protect sensitive data and provide an enhanced security environment for virtualized systems.

In summary, AMD64 is a powerful and versatile architecture that extends the capabilities of x86, offering enhanced memory addressing, backward compatibility, multi-core processing, vector extensions, and robust security features. These innovations have positioned AMD as a strong competitor in the computing landscape, catering to the demands of modern users and applications. The continuous evolution of AMD64 technology demonstrates AMD's commitment to pushing the boundaries of computing performance and efficiency.
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