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library: add a 'CPU_ZEROTICS' equivalent to <STAT> api

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This patch just implements an equivalent to the master
branch 'CPU_ZEROTICS' provision. However, the original
impetus for that earlier implementation was ultimately
attributed to a likely kernel anomaly since corrected.

As a result, in this newlib implementation we take the
opposite approach to the default behavior. There is no
adjustment to TIC_SUM_DELTA values if fewer ticks than
expected are recorded, unless the define is activated.

The commit shown below explains why the 'CPU_ZEROTICS'
define was retained in spite of the fix to the kernel.

Reference(s):
. issue referencing CPU_ZEROTICS
https://gitlab.com/procps-ng/procps/issues/132
. master branch CPU_ZEROTICS summary
commit ee3ed4b45e
. lengthy thread leading to CPU_ZEROTICS
https://www.freelists.org/post/procps/CStates-handling-new-switch

Signed-off-by: Jim Warner <james.warner@comcast.net>
This commit is contained in:
Jim Warner 2019-06-03 00:00:00 -05:00 committed by Craig Small
parent 40883a0b85
commit 1d8d4be046
1 changed files with 29 additions and 0 deletions
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29
proc/stat.c
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@ -46,6 +46,17 @@
//#define ENFORCE_LOGICAL // ensure only logical items are accepted by reap |
// ------------------------------------------------------------------------- +
/* --------------------------------------------------------------------------+
this next define is equivalent to the master top's CPU_ZEROTICS provision |
except that here in newlib we'll take an opposite approach to our default | */
//#define CPU_IDLE_FORCED // show as 100% idle if fewer ticks than expected |
// --------------------------------------------------------------------------+
#ifdef CPU_IDLE_FORCED
/* this is the % used in establishing a ticks threshold below which some |
cpu will be treated 'idle' rather than reflect misleading tick values | */
#define TICS_THRESHOLD ( 100 / 20 )
#endif
struct stat_jifs {
unsigned long long user, nice, system, idle, iowait, irq, sirq, stolen, guest, gnice;
@ -72,6 +83,9 @@ struct hist_tic {
int count;
struct stat_jifs new;
struct stat_jifs old;
#ifdef CPU_IDLE_FORCED
unsigned long edge; // only valued/valid with cpu summary |
#endif
};
struct stacks_extent {
@ -582,6 +596,13 @@ static int stat_read_failed (
return 1;
}
stat_derive_unique(sum_ptr);
#ifdef CPU_IDLE_FORCED
/* if any cpu accumulated substantially fewer tics than what is expected |
we'll force it to be treated as 'idle' so as not to return misleading |
statistics (and that sum_ptr->count also serves as first time switch) | */
if (sum_ptr->count) sum_ptr->edge =
((sum_ptr->new.xtot - sum_ptr->old.xtot) / sum_ptr->count) / TICS_THRESHOLD;
#endif
i = 0;
reap_em_again:
@ -604,6 +625,14 @@ reap_em_again:
break; // we must tolerate cpus taken offline
}
stat_derive_unique(cpu_ptr);
#ifdef CPU_IDLE_FORCED
// first time through (that priming read) sum_ptr->edge will be zero |
if (cpu_ptr->new.xtot < sum_ptr->edge) {
cpu_ptr->old.xtot = cpu_ptr->old.xbsy = cpu_ptr->old.xidl = cpu_ptr->old.xusr = cpu_ptr->old.xsys
= cpu_ptr->new.xbsy = cpu_ptr->new.xusr = cpu_ptr->new.xsys = 0;
cpu_ptr->new.xtot = cpu_ptr->new.xidl = 1;
}
#endif
++cpu_ptr;
++i;
} while (i < info->cpus.hist.n_alloc);