Performance Briefs
Hyper-Threading in UP and DP Systems
Will Wade (), Paul Martin (). Updated 4/9/2003

Summary: Hyper-Treading can provide significant performance boosts for both UP and DP systems. While there are benefits as high as 15-35% in specific scenarios, there can be negative impacts in some scenarios. Careful evaluation is required. If overall system performance is critical, a DP configuration is a better starting bet for common multitasking and increasingly-common multithreaded application environments.

Background: Hyper-Threading (HT) is a technology from Intel that doubles the number of “logical” processors in a system by adding a small amount of circuitry to Intel® Xeon™ processors and Pentium®4 CPUs and the associated chipsets. The HP xw4100, xw6000 and xw8000 workstations all support HT on WindowsXP and Redhat 7.1 or later.

Results: Two systems were measured – an xw4100 with a single 3Ghz Pentium 4 CPU and an xw8000 with two 3.06Ghz Xeon CPUs. In order to stress the systems as a high-end user might, two benchmarks were run concurrently under Windows-XP: (1) an Excel-based macro that performs a Monte Carlo simulation and (2) a Unigraphics v18 benchmark. As shown in the graph below, with HT off, both benchmarks ran significantly faster on the xw8000 – the combination averaging a 1.76x speedup.

The tests were then re-run with Hyper-Threading (HT) on, doubling the number of “logical” CPUs in the systems. For these tests, the xw4100 saw significant improvements with HT enabled, averaging a 30% improvement. The xw8000 also saw a significant speedup with HT on, and averaged over 55% faster than the xw4100 with HT on. Interestingly, the Unigraphics performance dropped about 10% with HT on the xw8000, and this amount varied run-to-run. While HT doubles the number of logical processors, contention for other system resources can become limiting or even negative factors. Examples include: processor arithmetic units and cache (which aren’t doubled with HT on), disk performance, and OS scheduling and overhead. Performance drops are occasionally observed with HT On. Thus, it is important to carefully evaluate the effect of HT in the customer’s specific environment.

Conclusion: Hyper-Treading can provide significant performance boosts for both UP and DP systems, but careful evaluation is needed. If overall system performance is critical, a DP configuration is the best starting bet for common multitasking and increasingly-common multithreaded application environments. The HP xw6000 and xw8000 Personal Workstations offer out-of-the-box DP performance or upgradeable UP configurations.

Links

TCL Performance Brief on Hyper-Threading (http://tclperf.fc.hp.com/performance_briefs/docs/2003-03-28Hyperthreading.doc)