Rafael C. de Almeida wrote: > Hello, > > I'm interested in knowing how the cpu data from /proc/stat is gathered. > Following my way from this function: > http://lxr.linux.no/linux+v2.6.25.10/fs/proc/proc_misc.c#L459 > I've figured that the time is probably gathered using those > account_*_time on sched.c. I'm not sure where the times are read from, > though. > > Anyhow, I thought I'd do a little test. I expected that if I added > together all the values on the cpu line of /proc/stat, waited 1 second > and added together all the values again, then their difference would be > a constant value. That is, the value should be the same any time I would > repeat the experiment. My reasoning was that those values accounted for > some unit of time and that the amount of time units between seconds > should always be the same. I expected a small variation due to the > kernel not always being able to wake the process that was doing the > measurement in exactly one second. <snip> > I found those values rather odd. There were 40 values above 200 and 7 > above 300. I didn't expect those big values to show up. I think there > might be a relation between the system utilization and the variation, > but I'm not sure. Why does it happen? Should I ask this on lkml as well? I runned a few cpu-bound process and it didn't make for big variations. Now, if I'd do dd if=/dev/zero of=/tmp/foo then I'd experience big variations on the values. I really can't understand what's going on here :-/. -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
