On Thu, 16 Jun 2005, Globe Trotter wrote:
Hi,
Here is an example cooked up just to show how it works. Only done with utime and stime, but can be extended to the other two in exactly the same way. But I wonder, which should be used? As per the manpage for times(2), the function reports the value of four times in four fields. 1) The tms_utime field contains the CPU time spent executing instructions of the calling process. 2) The tms_stime field contains the CPU time spent in the system while executing tasks on behalf of the calling process. 3) The tms_cutime field contains the sum of the tms_utime and tms_cutime values for all waited-for terminated children. 4) The tms_cstime field contains the sum of the tms_stime and tms_cstime values for all waited-for terminated children.
My programs go into an algorithm and do lots of things. Which times shoudl I use? I don't understand all this much: I am considering using the tms_utime field, but I don't know if I should use that or the sum of the first two or all of them. Any suggestions: I guess I really don't know what all these different times mean.
It depends what you want to do with the results.
Usually, the time you care about for mathematical algorithm comparisons is the user time. The system time is charged for the system parts of doing i/o, paging, task switching, etc. If you're benchmarking a database transaction system, for example, you may care about both user and system times.
For example, when you issue an i/o call in your program, that call invokes a system service that actaully copies the bytes between the device and the buffer in memory where you get or put the data. That system service's CPU time is charged to tms_stime. If you type on the keyboard in another teriminal while your job is running, your job is suspended, the keyboard input handler is invoked, and the job in the other terminal gets a chance to handle the event. Eventually, your job gets its turn again, and the sytem has to set it up and resume it. The time the system spends stopping and resuming your job is charged to tms_stime.
If your code doesn't spawn child processes (if you aren't sure, then it's a pretty safe bet it doesn't), then tms_cutime and tms_cstime will be zero anyway.
Many thanks and best wishes!
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