Should most of getrusage's fields be 0?

Question

I've written two system calls in linux, and I measure both of their resource usages with getrusage within the system call. However, most of the results I get are 0, and I'm not sure if that makes sense. Here's the output:

[ 4103.028728] DELTA RESULTS:
[ 4103.028746] u.tv_sec: 0
[ 4103.028748] s.tv_sec: 0
[ 4103.028749] u.tv_usec: 0
[ 4103.028751] s.tv_usec: 971765
[ 4103.028753] maxrss: 0
[ 4103.028755] ixrss: 0
[ 4103.028756] idrss: 0
[ 4103.028758] isrss: 0
[ 4103.028760] minflt: 0
[ 4103.028761] majflt: 0
[ 4103.028763] nswap: 0
[ 4103.028765] inblock: 0
[ 4103.028766] oublock: 0
[ 4103.028768] msgsnd: 0
[ 4103.028769] msgrcv: 0
[ 4103.028771] nsignals: 0
[ 4103.028773] nvcsw: 199
[ 4103.028774] nivcsw: 5

[ 4103.028961] CONTROL RESULTS:
[ 4103.028966] u.tv_sec: 0
[ 4103.028968] s.tv_sec: 0
[ 4103.028970] u.tv_usec: 1383
[ 4103.028972] s.tv_usec: 971998
[ 4103.028974] maxrss: 2492
[ 4103.028975] ixrss: 0
[ 4103.028977] idrss: 0
[ 4103.028978] isrss: 0
[ 4103.028980] minflt: 75
[ 4103.028982] majflt: 0
[ 4103.028984] nswap: 0
[ 4103.028986] inblock: 24
[ 4103.028987] oublock: 0
[ 4103.028989] msgsnd: 0
[ 4103.028991] msgrcv: 0
[ 4103.028992] nsignals: 0
[ 4103.028994] nvcsw: 200
[ 4103.028996] nivcsw: 5

I just want to know if this output is passable, or if it's a sign that somethings wrong, so I didn't put any of the source code. Thank you!

Answer 1

This looks right; I would not expect the syscall to make any changes in the vast majority of these metrics, which are measuring resources accounted to the process, not kernel resources. You should only see a change if you make a syscall like mmap that allocates new resources to the process, or one like read that ends up storing to previously copy-on-write memory belonging to the process.

With that said, I don't think calling getrusage like this makes much sense at all. It's normally for getting aggregate usage over a process's lifetime, not measuring deltas. Some of the more esoteric things may be hard to measure deltas for in other ways, but just time (real or cpu) can be measued via clock_gettime.