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library: fix an insidious bug affecting TICS_ALL_DELTA

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This simple two line code change fixes an intermittent
bug whereby %CPU for parent(s) with collapsed children
could be vastly understated from those displayed under
the current 3.3.17 publicly available top & libprocps.

If one started several top instances in the background
using very a small delay interval (zero?), then if the
shell under which they were running was collapsed, you
would see similar %CPU results for both the libraries.

However, when running a demanding 'make' like a kernel
compile (especially if backed by fast processors and a
SSD), then newlib would generally show only 1/3 to 1/2
of the collapsed %CPU values that appeared for 3.3.17.

Of course, now that the bug has been swatted with this
commit the disparities between those results is easily
explained. Since newly created tasks never contributed
tics during the interval where they were created, only
with many short lived tasks would differences surface.

Signed-off-by: Jim Warner <james.warner@comcast.net>
This commit is contained in:
Jim Warner 2021-04-22 00:00:00 -05:00 committed by Craig Small
parent 0f691226ec
commit c082779769
1 changed files with 4 additions and 1 deletions
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5
proc/pids.c
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@ -645,10 +645,13 @@ static inline int pids_make_hist (
pids_histput(info, slot);
if ((h = pids_histget(info, p->tid))) {
p->pcpu = tics - h->tics;
tics -= h->tics;
p->maj_delta = p->maj_flt - h->maj;
p->min_delta = p->min_flt - h->min;
}
/* here we're saving elapsed tics, which will include any
tasks not previously seen via that pids_histget() guy! */
p->pcpu = tics;
info->hist->num_tasks++;
return 1;