Hyper-Threading Technology, New Feature of Intel Xeon Processor White Paper
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Figure 4:
In a Hyper-Threaded processor, the processor resources are shared so that each thread uses a
different resource during each clock cycle. The goal is that the additional thread will fill the voids
in the pipeline and take over processor resources when one thread is stalled, while waiting on a
cache miss to be filled. With this limitation, some applications will not benefit from the Hyper-
Threading technology.
A majority of single-threaded applications will not benefit. This can be seen from the Sysmark
and Winstone Benchmark results. (See the Performance Analyses section for details.)
Additionally, some multi-threaded applications that are not specifically optimized for Hyper-
Threading technology might also show negative or no benefit. For example, the interleaved
thread will contend for resources and destroy the effectiveness of the tight code optimizations.
Both threads may also come into conflict over precious space in the trace cache.
Applications such as Internet audio and video streaming, high-performance 3D graphics, digital
photography and digital video encoding/decoding, speech recognition, multimedia, MP3
encoding, and database applications do benefit from Hyper-Threading technology. Naturally,
these applications are already multi-threaded and each thread is handling a different task that
works well with a Hyper-Threaded processor. In addition, these applications can take advantage
of the new 142 SSE2 new instructions. These new instructions reduce the overall number of
instructions required to execute a particular program task and, as a result, can contribute to an
increase in overall system performance.
