How many Context Switches is “normal”? This depends very much on the type of application you run. If you've got applications which are very trigger-happy WRT syscalls you can expect to see high amounts of context switching. If most of your applicatio…

从Java视角理解系统结构连载, 关注我的微博(链接)了解最新动态   在高性能编程时,经常接触到多线程. 起初我们的理解是, 多个线程并行地执行总比单个线程要快, 就像多个人一起干活总比一个人干要快. 然而实际情况是, 多线程之间需要竞争IO设备, 或者竞争锁资源,导致往往执行速度还不如单个线程. 在这里有一个经常提及的概念就是: 上下文切换(Context Switch). 上下文切换的精确定义可以参考: http://www.linfo.org/context_switch.html. 下…

A context switch (also sometimes referred to as a process switch or a task switch) is the switching of the CPU (central processing unit) from one process or thread to another. A process (also sometimes referred to as a task) is an executing (i.e., ru…

The context is represented in the PCB of the process. It includes the value of the CPU registers, the process state (see Figure 3.2), and memory-management information. 上下文是保存在PCB里面的. 它包括了CPU寄存器的值, 进程状态, 和内存管理信息. Generically, we perform a state save…

什么是CPU上下文切换? 现在linux是大多基于抢占式,CPU给每个任务一定的服务时间,当时间片轮转的时候,需要把当前状态保存下来,同时加载下一个任务,这个过程叫做上下文切换.时间片轮转的方式,使得多个任务利用一个CPU执行成为可能,但是保存现场和加载现场,也带来了性能消耗.  那线程上下文切换的次数和时间以及性能消耗如何看呢?                ​    ​如何获得上下文切换的次数? vmstat直接运行即可,在最后几列,有CPU的context switch次数. 这个是系统层…

In computing, a context switch is the process of storing and restoring the state (more specifically, the execution context) of a process or thread so that execution can be resumed from the same point at a later time. This enables multiple processes t…

How long does it take to make a context switch?   FROM: http://blog.tsunanet.net/2010/11/how-long-does-it-take-to-make-context.html That's a interesting question I'm willing to spend some of my time on. Someone at StumbleUpon emitted the hypothesis t…

FROM: http://blog.tsunanet.net/2010/11/how-long-does-it-take-to-make-context.html That's a interesting question I'm willing to spend some of my time on. Someone at StumbleUpon emitted the hypothesis that with all the improvements in the Nehalem archi…

16.2 How would you measure the time spent in a context switch? 上下文转换发生在两个进程之间,比如让一个等待进程进入执行和让一个运行进程进入等待,这些在多任务中发生.操作系统需要把等待进程的信息放入内存和把当前运行的进程信息保存下来.为了解决这个问题,我们记录在切换进程时的最后和第一个指令的时间点,比如我们有两个进程P1和P2,P1在执行P2在等待,当我们切换P1和P2时,假设发生在P1的第N个指令,我们用tx,k来表示进程x的第k个…

3.4 The Sun UltraSPARC processor has multiple register sets. Describe what happens when a context switch occurs if the new context is already loaded into one of the register sets. What happens if the new context is in memory rather than in a register…