PRESENTED BY:
G SURESH

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Abstract:
Intel’s Hyper-Threading Technology brings the concept of simultaneous multi-threading to the Intel Architecture. Hyper-Threading Technology makes a single physical processor appear as two logical processors; the physical execution resources are shared and the architecture state is duplicated for the two logical processors. From a software or architecture perspective, this means operating systems and user programs can schedule processes or threads to logical processors as they would on multiple physical processors. From a microarchitecture perspective, this means that instructions from both logical processors will persist and execute simultaneously on shared execution resources.
The first implementation of Hyper-Threading Technology was done on the IntelXeonprocessor MP. In this implementation there are two logical processors on each physical processor. The logical processors have their own independent architecture state, but they share nearly all the physical execution and hardware resources of the processor. The goal was to implement the technology at minimum cost while ensuring forward progress on logical processors, even if the other is stalled, and to deliver full performance even when there is only one active logical processor.
The potential for Hyper-Threading Technology is tremendous; our current implementation has only just begun to tap into this potential. Hyper-Threading Technology is expected to be viable from mobile processors to servers; its introduction into market segments other than servers is only gated by the availability and prevalence of threaded applications and workloads in those markets.
Introduction:
Hyper-Threading technology is a groundbreaking innovation from Intel that enables multi-threaded server software applications to execute threads in parallel within each processor in a server platform. The Intel® Xeon™ processor family uses Hyper-Threading technology, along with the Intel® NetBurst™ microarchitecture, to increase compute power and throughput for today’s Internet, e-Business, and enterprise server applications. This level of threading technology has never been seen before in a general-purpose microprocessor. Hyper-Threading technology helps increase transaction rates, reduces end-user response times, and enhances business productivity providing a competitive edge to e-Businesses and the enterprise. The Intel® Xeon™ processor family for servers represents the next leap forward in processor design and performance by being the first Intel® processor to support thread-level parallelism on a single processor.
With processor and application parallelism becoming more prevalent, today’s server platforms are increasingly turning to threading as a way of increasing overall system performance. Server applications have been threaded (split into multiple streams of instructions) to take advantage of multiple processors. Multi-processing-aware operating systems can schedule these threads for processing in parallel, across multiple processors within the server system. These same applications can run unmodified on the Intel® Xeon™ processor family for servers and take advantage of thread-level-parallelism on each processor in the system. Hyper-Threading technology complements traditional multi-processing by offering greater parallelism and performance headroom for threaded software.
Overview of Hyper-Threading Technology:
Hyper-Threading technology is a form of simultaneous multi-threading technology (SMT), where multiple threads of software applications can be run simultaneously on one processor. This is achieved by duplicating the architectural state on each processor, while sharing one set of processor execution resources. The architectural state tracks the flow of a program or thread, and the execution resources are the units on the processor that do the work: add, multiply, load, etc.
Dual-processing (DP) server applications in the areas of Web serving, search engines, security, streaming media, departmental or small business databases, and e- mail/file/print can realize benefits from Hyper-Threading technology using Intel® Xeon™ processor-based servers.
History:
The hyper-threading technology found its roots in Digital Equipment Corporation but was brought on the market by Intel. Hyper-Threading was first introduced in the Foster MP-based Xeon in 2002. It appeared on the 3.06 GHz Northwood-based Pentium 4 in the same year, and then appeared in every Pentium 4 HT, Pentium 4 Extreme Edition and Pentium Extreme Edition processor. Previous generations of Intel's processors based on the Core microarchitecture do not have Hyper-Threading, because the Core microarchitecture is a descendant of the P6 microarchitecture used in iterations of Pentium since the Pentium Pro through the Pentium III and the Celeron (Covington, Mendocino, Coppermine and Tualatin-based) and the Pentium II Xeon and Pentium III Xeon models.
Intel released the Nehalem (Core i7) in November 2008 in which hyper-threading makes a return. The first generation Nehalem contains 4 cores and effectively scales 8 threads. Since then, both 2- and 6-core models have been released, scaling 4 and 12 threads respectively.
The Intel Atom is an in-order processor with hyper-threading, for low power mobile PCs and low-price desktop PCs.
The Itanium 9300 launched with eight threads per processor (2 threads per core) through enhanced hyper-threading technology. Poulson, the next-generation Itanium, is scheduled to have additional hyper-threading enhancements.
The Intel Xeon 5500 server chips also utilize two-way hyper-threading.