Commits on Oct 23, 2023

1. metrics: prevent negative counter from iowait decrease …

   The iowait metric obtained from `/proc/stat` can under some circumstances
   decrease. The relevant condition is when an interrupt arrives on a different
   core than the one that gets woken up for the IO, and a particular counter in the
   kernel for that core gets interrupted. This is documented in the man page for
   the `proc(5)` pseudo-filesystem, and considered an unfortunate behavior that
   can't be changed for the sake of ABI compatibility.
   
   In Nomad, we get the current "busy" time (everything except for idle) and
   compare it to the previous busy time to get the counter incremeent. If the
   iowait counter decreases and the idle counter increases more than the increase
   in the total busy time, we can get a negative total. This previously caused a
   panic in our metrics collection (see #15861) but that is being prevented by
   reporting an error message.
   
   Fix the bug by putting a zero floor on the values we return from the host CPU
   stats calculator.
   
   Fixes: #15861
   Fixes: #18804

   

   tgross committed Oct 23, 2023
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