kern/78957: time counter per process stops (syscall: getrusage)

[Bruce Evans]

On Thu, 17 Mar 2005, Jakub Kruszona-Zawadzki wrote:

>> Description:
> When a process is running for a long time (several days) time counter per process stops on value:
> ru_utime.tv_sec:305221
> ru_utime.tv_usec:322735

This may be the same bug as in PR 76972.  Overflow occurs at about
48592008 ticks = 379625 seconds = 105 hours for a a process that consumes
100% of the CPU if the statclock frequency is 128 Hz (which is the default
and not easy to change).  There is another overflow bug at 2^32 ticks = 388
days.  This one is harder to fix.  See PR 76972 for details and a fix for
the first overflow bug.

37965 seconds is a little larger than 305221 seconds.  The difference might
be due to the other 70000+ seconds being in ru_stime.

The behaviour when overflow occurs is undefined, but stopping on a value
is quite likely to occur due to the algorithm for updating ru_*time.
Integer overflow tends to cause counters to reset to 0 (or INT_MIN),
but the kernel enforces monotonicity of the usage times, so they will
stick instead of going backwards to 0.

Bruce