On Sun, Oct 23, 2005 at 22:50:44 +0200, Claudio Scordino wrote: > Hi all. > > I need some help to make profiling of an application on Linux. I need to > measure the computation time between different points of my program, > considering only the CPU time that the task has actually executed (i.e. > without the intervals of time that the task has been preempted by other > tasks). > > To accomplish that, I can't just read the current time in different parts of > the program, nor I can set and use a timer, because this wouldn't consider > preemptions... That's what profiler is for. There is a profiler in the GNU compiler suite, called gprof. Does that not fullfill your needs? > I found out that Linux provides the getrusage() syscall which provides the > information that I need. This syscall also says both user and system times > used by the task, which is a very useful thing. > > However, it has two main drawbacks: > > - its precision is very low: I'm working with real-time tasks on a Athlon-64 > and I need a more accurate estimation Yes, it's jiffies. > - it can't be invoked by a generic task to know the execution time of another > task > > The only idea that I had is to insert some hooks in the kernel functions and > use some high resolution timer to compute the time that my task has > actually executed. This timer starts whenever the task obtains the CPU, and is > stopped whenever the task yields the CPU. > > Therefore, I just need to know which functions are invoked when a task starts > executing on the CPU and when it looses the CPU. Task switching always boils down to schedule(). Plus the user/system time distinction must be handled in kernel entry/exit. Actually you want to look where task->signal->utime and task->signal->stime (for any value of task, most often current) are updated and hook there. -- Jan 'Bulb' Hudec <bulb@xxxxxx>
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