What is hyper-Threading technology in the CPU

Hyper-Threading technology is a CPU at the same time to execute multiple programs to share a CPU resources, in theory, like two CPUs at the same time executing two threads, P4 processors need to add a logical CPU pointer (logical processing unit). So the die of the new generation of P4 HT is 5% larger than the previous P4. The rest, such as the ALU (integer unit of operation), FPU (floating-point unit), L2 cache (level two caching) remain unchanged, and these parts are shared.

Although using Hyper-Threading technology can execute two threads at the same time, it is not like two real CPUs, and each CPU has a separate resource. When two threads need a resource at the same time, one of them stops temporarily and yields resources until the resources are idle to continue. Therefore, the performance of Hyper-threading is not equal to the performance of two CPUs.

Hyper-Threading and performance promotion

A lot of people would think that using hyper-threading technology would improve the performance of the system, but is that really the case? Don't forget the requirements for the hyper-Threading technology implementation that we talked about earlier, which is a prerequisite for hyper-Threading technology to be effective. In addition to operating system support, you must also support the software. From this we can see that, in the current software status, the support of dual-processor technology is still in the minority. For most software, there is no direct benefit from hyper-Threading technology at present because of the different principles of design. Because Hyper-Threading technology is a parallel processing command at the thread level, resources such as processors are dynamically allocated by thread. The core idea of the technology is "parallelism (Parallelism)", which is to improve the parallelism of command execution and improve the efficiency of each clock. This requires the software in the design of the online process, improve the ability of parallel processing. Currently, applications on PCs are rarely optimized for this, and using Hyper-Threading technology does not provide a significant boost to performance.

The inevitability of the emergence of HT technology

Increased CPU performance needs

Although improving CPU clock frequency and increased cache capacity can indeed improve CPU performance, but such CPU performance is more difficult to improve technology. In fact, in the application for many reasons, the CPU's execution unit is not fully used. If the CPU does not read data properly (bus/memory bottlenecks), its execution unit utilization is significantly reduced. The other is that most execution threads currently lack ILP (Instruction-level Parallelism, multiple directives executing simultaneously) support. All of this has caused the current CPU performance not to be fully played. As a result, Intel uses another idea to improve CPU performance, allowing the CPU to execute multiple threads simultaneously, allowing the CPU to perform more efficiently, known as "Hyper-threading (Hyper-threading," "HT") technology. Hyper-Threading technology is to use special hardware instructions to simulate two logical cores into two physical chips, so that a single processor can use thread-level parallel computing, which is compatible with multi-threaded operating systems and software, reduce CPU idle time, improve the efficiency of the CPU.

With Hyper-threading in time, applications can use different parts of the chip at the same moment. Although a single threaded chip can handle thousands of instructions per second, only one instruction can be manipulated at any one time. and hyper-Threading technology can make the chip simultaneously multithreading, so that the chip performance is improved.

Hyper-Threading Technology

Intel P4 Hyper-Threading has two operating modes, single task mode and multi task modes (multitasking mode), when the program does not support multi-processing (multiprocessor jobs), the system will stop the operation of one of the logical CPUs, Focus resources on a single logical CPU, allowing single-threaded routines to not be idle by one of the logical CPUs, but because the logical CPUs that are stopped are still waiting to work, consuming a certain amount of resources, the Hyper-threading CPU runs the task mode, you may not be able to achieve CPU performance without Hyper-threading functionality, but the performance gap is not too great. That is, hyper-threading technology can even degrade system performance when running single-threaded software, especially when multithreaded operating systems run single-threaded software.

It is important to note that CPUs that contain hyper-threading technology require chipsets, software support, to make the technology more desirable. Operating systems such as Microsoft Windows XP, and Microsoft Windows 2003,linuxkernel 2.4.x versions also support Hyper-Threading technology.