什么是＆QUOT; CPU时间＆QUOT; （使用Android的PS -x）？ [英] What is "CPU time" (using Android's ps -x)?

问题描述

所以我想写收集CPU时间的进程Java函数，并将它们与之前的读数来确定CPU时间的进程已经要求自上次取样。我发现了如何从本网站的 HTTP：//$c$cseekah.com/2012/10/21/android-shell-tricks-ps/

So I'm trying to write a Java function that gathers CPU time for processes, and compares them to prior readings to determine the CPU time a process has demanded since the last sample was taken. I found out how to get the CPU time of processes from this site http://codeseekah.com/2012/10/21/android-shell-tricks-ps/

基本上，你可以执行PS -x，并添加你在最后看到的值;它们看起来像这样（U：15，S：854）。的问题是，我似乎比预期的要获得更高的值。我理解这里这个页面的方式 http://en.wikipedia.org/wiki/CPU_time#Total_CPU_time < /一>是，在给定的壁的时间间隔最大CPU时间（核数）*（壁时间间隔）。我的测试设备具有4个核心，而我每3秒采样。我从电流值减去previous，而且经常看到高于12秒最终值。那可能吗？我是misinter preting的数据？我会后下面

Basically, you can execute "ps -x" and add the values you see at the end; they look like this (u:15, s:854). The problem is that I seem to be getting higher values than expected. The way I understand this page here http://en.wikipedia.org/wiki/CPU_time#Total_CPU_time, is that the maximum CPU time in a given wall time interval is (number of cores)*(wall time interval). My testing device has 4 cores, and I am sampling every 3 seconds. I subtract previous from current values, and often see final values that are above 12 seconds. Is that possible? Am I misinterpreting the data? I'll post some code snippets below

if (currentNameAndTime.get(i).processName.equals(oldNameAndTime.get(j).processName)) {
    // If they match, subtract the CPU times, and store the
    // result in the time field
    obj.time = (currentNameAndTime.get(i).time - oldNameAndTime.get(j).time);
    // Add the object to the array that will be returned
    finalNameAndTime.add(obj);
    // Break the chain, as after a match is found, all other
    // name comparisons will fail
    break;
}
if (oldNameAndTime.size() == 0) {
        FgBgCPUInfo obj = new FgBgCPUInfo();
        obj.processName = "FIRST RUN";
        obj.time = 0;
        finalNameAndTime.add(obj);
    }
oldNameAndTime = new ArrayList<FgBgCPUInfo>(currentNameAndTime);

感谢您！

推荐答案

的值是CPU和时钟滴答系统时间。该定义可以在从桌面系统中的 5人PROC 文本中找到：

The values are CPU and system time in clock ticks. The definition can be found in the man 5 proc text from a desktop system:

          utime %lu   Amount of time that this process has been  scheduled
                      in  user  mode,  measured  in clock ticks (divide by
                      sysconf(_SC_CLK_TCK).   This  includes  guest  time,
                      guest_time  (time  spent  running a virtual CPU, see
                      below), so that applications that are not  aware  of
                      the  guest  time  field  do  not lose that time from
                      their calculations.

          stime %lu   Amount of time that this process has been  scheduled
                      in  kernel  mode, measured in clock ticks (divide by
                      sysconf(_SC_CLK_TCK).

该值每线程跟踪，所以你应该使用 PS -t -x 来查看每个进程的所有线程。如果没有 -t 你只是在看统计信息为主线，这可能是为什么你的号码对不上号。

The values are tracked per-thread, so you should be using ps -t -x to see all threads in each process. Without -t you're just looking at the stats for the main thread, which may be why your numbers don't add up.

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