What is hyperthreading technology?
By Vincents Garballey 2020-01-06 1733 151
Although it is possible to execute two threads at the same time with hyper-threading technology, it is not like two real CPU, each CPU has independent resources. When both threads need a resource at the same time, one of them temporarily stops and gives up the resource until the resource is idle. Therefore, the performance of hyperthreading is not equal to the performance of two CPU.
Hyperthreading and performance improvement
Generally speaking, many people will think that the use of hyperthreading technology can greatly improve the performance of the system, but is this really the case? Don't forget the necessary conditions for the implementation of hyper-threading technology that we mentioned earlier, which is a prerequisite for the effectiveness of hyper-threading technology. In addition to operating system support, software support is also required. From this point, we can see that, in terms of the current software situation, the software that supports dual-processor technology is still in a small number after all. For most software, due to the different principles of the design, we can not get the direct benefit from the hyperthreading technology. Because hyper-threading technology processes commands in parallel at the thread level and dynamically allocates processors and other resources according to threads. The core idea of this technology is & amp;ldquo; parallelism (Parallelism) ", that is, to improve the parallelism of command execution and the efficiency of each clock. This requires the software to be threaded in design and improve the ability of parallel processing. At present, the applications on PC have hardly been optimized for this, and the use of hyper-threading technology has not been able to achieve a significant improvement in performance. The inevitability of the emergence of
CPU performance improve
It is necessary to improve the performance of CPU. Although it is true that increasing the clock frequency and cache capacity of CPU can improve the performance of CPU, it is technically difficult to improve the performance of CPU. In fact, for many reasons in the application, the execution unit of CPU is not fully utilized. If CPU cannot read data properly (bus / memory bottleneck), its execution unit utilization will decrease significantly. In addition, most of the current execution threads lack ILP (Instruction-Level Parallelism, multiple instruction execution at the same time) support. All these have resulted in the lack of full play of the current performance of CPU. Therefore, Intel adopts another idea to improve the performance of CPU, so that CPU can execute multiple threads at the same time, which can make CPU more efficient, that is, the so-called "hyperthreading (Hyper-Threading, referred to as" HT ") technology. Hyper-threading technology uses special hardware instructions to simulate two logic 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, reduces the idle time of CPU and improves the running efficiency of CPU.
Using hyperthreading in time allows applications to use different parts of the chip at the same time. Although a single-threaded chip can process thousands of instructions per second, it can only operate on one instruction at any one time. The hyper-threading technology can make the chip carry out multi-thread processing at the same time, so that the performance of the chip can be improved.
Intel P4 hyperthreading has two running modes:, Single Task Mode (single-task mode and Multi Task Mode (multitasking mode). When the program does not support Multi-Processing (multiprocessor jobs), the system will stop the operation of one of the logical CPU and concentrate resources on a single logical CPU, so that the performance of the single-threaded program will not be degraded because one of the logical CPU is idle, but the stopped logical CPU will still wait for work. It takes up a certain amount of resources, so when Hyper-Threading CPU runs Single Task Mode program mode, it may not be able to achieve CPU performance without hyper-threading, but the performance gap will not be too great. In other words, when running single-threaded software, hyperthreading technology will even reduce system performance, especially when multithreaded operating system runs single-threaded software.
It should be noted that CPU with hyperthreading technology needs chipset and software support in order to give full play to the advantages of this technology. Operating systems such as: Microsoft Windows XP, Microsoft Windows 2003 and later versions of Linux kernel 2.4.x also support hyper-threading technology.
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