操做系统之SMP和AMP系统

    SMP——Symmetric Multi-Processing (SMP)，即对称多处理器结构

    AMP——Asymmetric Multi-Processing (AMP) ，非对称多处理器结构

1.Linux查看是不是处于SMP环境

    如何查看咱们的Linux是SMP仍是AMP，以下List-1，参考博客《Linux确认工做在SMP环境中》

    List-1 "uname -a"命令的结果中含有SMP，这是个人CentOS7 64bits上的结果 

[dmj@localhost ~]$ uname -a
Linux localhost.localdomain 3.10.0-862.el7.x86_64 #1 SMP Fri Apr 20 16:44:24 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

    List-2 "uname -a"命令的结果中含有SMP，这是个人Ubuntu16 64bits上的结果

dmj@ubuntu:~$ uname -a
Linux ubuntu 4.4.0-62-generic #83-Ubuntu SMP Wed Jan 18 14:10:15 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

2.AMP和SMP的特征对比

    AMP system的主要特征以下:

• multiple CPUs
• each of which may be a different architecture [but can be the same]
• each has its own address space
• each may or may not run an OS [and the OSes need not be the same]
• some kind of communication facility between the CPUs is provided

    SMP system的主要特征以下:

• multiple CPUs
• each of which has the same architecture
• CPUs share memory space [or, at least, some of it]
• normally an OS is used and this is a single instance that runs on all the CPUs, dividing work between them
• some kind of communication facility between the CPUs is provided [and this is normally shared memory]

    SMP的特征是：只有一个操做系统实例，运行在多个CPU上，每一个CPU的结构都是同样的，内存、资源共享。这种系统有一个最大的特色就是共享全部资源。

    AMP的特征是：多个CPU，各个CPU在架构上不同，每一个CPU内核运行一个独立的操做系统或同一操做系统的独立实例，每一个CPU拥有本身的独立资源。这种结构最大的特色在于不共享资源。

    咱们平时使用的机器基本都是SMP system，我目前尚未见过AMP system。

    因此为何说Java的伪共享在SMP系统上严重，经过SMP系统的特性能够明白——由于SMP系统共享资源，关于伪共享，能够查看个人另外一篇博客。

 

Reference:

1. http://scitechconnect.elsevier.com/asymmetric-multi-processing-amp-vs-symmetric-multi-processing-smp/
2. https://blog.csdn.net/honour2sword/article/details/45248121
3. http://www.javashuo.com/article/p-zvzhkjui-bo.html