Messages in this thread | | | Date | Sun, 8 Jul 2007 20:19:21 +0200 | From | wixor <> | Subject | getrusage time measurements variations |
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Hello all, I've been doing some getrusage tests using this:
#include <stdio.h> #include <unistd.h> #include <sys/resource.h>
int main(void) { unsigned int i; struct rusage ru; for(i=1;i;i++) asm volatile("nop"); getrusage(RUSAGE_SELF, &ru); printf("%dsec %dusec\n",ru.ru_utime.tv_sec,ru.ru_utime.tv_usec); return 0; }
What is good is that results do not seem to depend on other thread activity nor disk i/o. However, each time I run this program, result varies (from 4.039 sec to 4.062 sec). Does the actual execution time change each time? User time should not contain .so library loading time, nor memory allocation time (kernel part) nor anything like this. Does getrusage measure time so accurately (1usec precision), even if HZ is set to, let's say, 100?
But that's not very bad... Problems start, when I run this with heavy network i/o load. I'm using ne1000 network adapter (on isa bus... well, that's very old stuff), which seem to generate interrupt on each packet it receives - top reports very high "hi" values, up to 20%. Results from getrusage change to 5.2 sec. Is this variation the same one as above, but in greater scale? Can this be eliminated?
My problem is, that I'd like to measure user time of process with 1msec resolution, but what is most important, I want the result to be the same each time I run program. Can it be done with standard linux kernels, or should I try some "real-time" versions?
Thanks for responses, and please CC me, I'm not in the list. -- wixor - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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