Hyper-Threading Technology Impact on Compute-Intensive Workloads

Short Description
Intel’s recently introduced Hyper-Threading Technology promises to increase application- and system-level performance through increased utilization of processor resources. It achieves this goal by allowing the processor to simultaneously maintain the context of multiple instruction streams and execute multiple instruction streams or threads. These multiple streams afford the processor added flexibility in internal scheduling, lowering the impact of external data latency, raising utilization of internal resources, and increasing overall performance.

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Content
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While the most visible indicator of computer performance is its clock rate, overall system performance is also proportional to the number of instructions retired per clock cycle. Ever-increasing demand for processing speed has driven an impressive array of architectural innovations in processors, resulting in substantial improvements in clock rates and instructions per cycle.
One important innovation, super-scalar execution, exploits multiple execution units to allow more than one operation to be in flight simultaneously. While the performance potential of this design is enormous, keeping these units busy requires super-scalar processors to extract independent work, or instructionlevel parallelism (ILP), directly from a single instruction stream.
Modern compilers are very sophisticated and do an admirable job of exposing parallelism to the processor; nonetheless, ILP is often limited, leaving some internal processor resources unused. This can occur for a number of reasons, including long latency to main memory, branch mis -prediction, or data dependences in the instruction stream itself. Achieving additional performance often requires tedious performance analysis, experimentation with advanced compiler optimization settings, or even algorithmic changes. Feature sets, rather than performance, drive software economics. This results in most applications never undergoing performance tuning beyond default compiler optimization.
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