＆是什么QUOT;高无意的上下文＆QUOT;开关是什么意思？ [英] What does "high involuntary context" switches mean?
问题描述
我的重新编写在C code的一部分时使用的的getrusage（2） C API。
I have re-written a part of code in C. When testing it with logging the resource usage using getrusage(2) C API.
改变code之前：
user time (ms): 21503
system time (ms): 372
involuntary context switches: 20
变化后：
user time (ms): 25589
system time (ms): 80732
involuntary context switches: 821
我看到了很多非自愿的上下文切换被在code我已经重新编写完成。
I see a lot of involuntary context switches being done in the code I have re-written.
我的问题是不是的如何的减少上下文切换。但是..
My question is not about how to reduce context switches. But..
- 在非自愿上下文切换会发生什么情况都比较？
- 在什么样的方式会影响系统？
P.S：有是什么都没有写在磁盘上没有活动。它只是执行ping服务器几次。
P.S: There is no activity on the disk as nothing is being written. It just pings the server several times.
更新：
新增系统和用户花费时间。
Added system and user time taken.
程序是多线程的。线程（线程3K）的相同数量催生了两种情况。只有在C中的底层API被改写。
Program is multi-threaded. Same number of threads (3k thread) are spawned in both the cases. Only the underlying api in C is being rewritten.
推荐答案
每当一个线程/进程进行系统调用，则可能发生volontary上下文切换阻止。
A volontary context switch can occur whenever a thread/process makes a system call that blocks.
当一个线程已经未做系统调用运行块太长（通常类似于10毫秒），就会发生involontary上下文切换，并有等待CPU的进程。
An involontary context switch occurs when a thread has been running too long (usually something like 10 ms) without making a system call that blocks and there are processes waiting for the CPU.
它看起来像你的程序是更多的CPU密集现在比以前。如果你做了它的多线程则同比增长可能是预期。
It looks like your program is more CPU-intensive now than before. If you have made it multi-threaded then an increase is probably expected.
821上下文切换 - 这取决于你的程序的执行时间，这可能是也可能不是很多。
821 context switches - depending on the execution time of your program this may or may not be a lot.
如果你想减少上下文的数量开关可以减少工作线程的数量，以便有较少的线程之外还有CPU内核。
If you want to reduce the number of context switches you can reduce the number of worker threads so there are less threads than there are CPU cores.
更新
假设负载是在两种情况下是相同的，它看起来像code的修改都提高了CPU使用率。如果增加的负载是一个问题，你应该分析code，找到瓶颈。 仪表可在隔离有助于其code的一部分，是造成问题。
Assuming that the load is identical in both cases, it looks like the code modifications have increased the cpu usage. If the increased load is a concern you should analyse the code to find the bottleneck. Instrumentation can be helpful in isolating which part of the code is causing the problem.
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