Re: Task profiling in Linux

[Claudio Scordino <cloud.of.andor@gmail.com>]

Thank you for your suggestion, but I still have a question about it. 

If I do

clock_gettime (CLOCK_THREAD_CPUTIME_ID, &old);
sleep(5);
clock_gettime (CLOCK_THREAD_CPUTIME_ID, &new);

why the difference (new-old) includes also the time the process has slept ?

Maybe there was a misunderstanding: I am looking for a way to know how long a 
process has _actually_ executed, accounting for all periods that it has not 
executed for some reason (like sleep, blocking, preemptions, etc.). And I 
need the high precision gave by the TSC (jiffies is not enough).

getrusage works fine, but has a coarse-grain precision (jiffies).
clock_gettime, instead, has a very good precision (thanks to TSC) but as you 
can see, it does not return the time that the process has actually 
executed...

If I am wrong, please tell me where.

Thank you,

            Claudio


On Monday 31 October 2005 18:15, you wrote:
> On 10/23/05, Claudio Scordino <cloud.of.andor@gmail.com> wrote:
> > 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...
>
> struct timespec start;
> clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &start);
>
> ... do work...
>
> struct timespec end;
> clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &end);
>
> ... subtract start from end
>
> Or use CLOCK_THREAD_CPUTIME_ID if this is more correct for your
> application.
>
> This works since Roland's clock work got added in the 2.6 series.
> Before that preemption wasn't excluded.
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